IAEA-120

ISOTOPES AND RADIATIONIN INVESTIGATIONS OF FERTILIZER AND

WATER USE EFFICIENCY

COUNTRIES OF ASIA AND THE FAR EAST

PROCEEDINGS OF A STUDY GROUP MEETINGCONVENED BY THE

JOINT FAO/IAEA DIVISION OF ATOMIC ENERGY, IN FOOD AND AGRICULTURE

AND HELD IN BANGKOK, THAILAND21-25 APRIL 1969

A TECHNICAL REPORT PUBLISHED BY THEINTERNATIONAL ATOMIC ENERGY AGENCY, VIENNA, 1970

The IAEA does not maintain stocks of reports in this series. However,microfiche copies of these reports can be obtained from

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ISOTOPES AND RADIATION IN INVESTIGATIONS OFFERTILIZER AND WATER USE EFFICIENCY -COUNTRIES OF ASIA AND THE FAR EAST.

Proceedings of a Study Group Meetingconvened by the Joint FAO/IAEA Divisionof Atomic Energy in Food and Agriculture,

held in Bangkok, ThailandApril 21-25, 1969.

IAEA - Vienna, 1970

CONTENTS

OPENING ADDRESSESH.E. M.R. Chakratong Tongyai .................................. 1D.A. Rennie ............................................*...... 3

RICE: PHYSIOLOGY, NUTRITION, FERTILIZATIONA review of the co-ordinated research programme on the applicationof isotopes to rice fertilization studies, 1962-1968 .............. 6

P.B. VoseStudies on the efficiency of time and method of fertilizerapplication for rice using N-15 and P-32 ......................... 15

M.W. ThenabaduStudies on the comparative nutrient requirements of low andhigh yielding varieties of rice .................................. 29

A.B. Khan, L. Rahtnan, S.I. Chowdhury, S.M. A lam,P.K. Deb and Y. Ali

A study on the efficiency of shallow and surface placement ofnitrogen and phosphorus fertilizers applied separately andchemically combined form by using isotope technique ............... 50

S.. SuwanHaong, P. Sanitwongse and P. SawatdeeRecent soil, fertilizer and physiological studies with P-32on high yielding varieties of paddy .............................. 61

B.V. Subbiah and J.C. KatyalThe effect of osmotic pressure on P-32 phosphate absorptionand leakage by excised rice roots and the adaptation of riceroots to varying osmotic pressures ............................... 82

Yuh-Jang ShiehEffect of silicon on the absorption of manganese and phosphorusin rice seedlings ................................................. 97

S.C. Shim, U. Jang-Kirl, Lee Hyong-Koo

NUTRITION STUDIES: PHOSPHORUSEvaluation of pyro- and metaphosphates as sources of phosphorusfor plants, I. Uptake studies in water culture ................. 104

A.K. Sinha and K.B. MistryReport on the use of radioisotope P-32 for fertilizer studiesin Indonesia .................................................... 122

Nazir Abdullah

CONTENTS ctd.

The significance of the 'A1 value concept in fieldfertilizer studies .............................................. 132

D.A. RennieFate of fertilizer nitrogen applied to soils .................... 146

J.O. LeggThe use of N-15 as a tracer in fertilize? efficiency study 'in Japan ......................................................... 161

S. Nishigaki

NUTRITION STUDIES: MOISTURE RELATIONSHIPSRadiation techniques as means of improving the efficiencyof water use ....................................................». 168.

Y. BarradaHater and ion movement in soils ................................. 179

W.R. GardneriThe effect, of asphalt barriers on the moisture and nutrients

retention in rice and sugarcane fields of sand soils ............ 183C.C. Wang, K.Y. Li, C.C. Yang, P.W. Ho and J.T. Wang

RECOMMENDATIONS ................................................. 192

LIST OP PARTICIPANTS ............................................ 194

FOREWORD

The Study Group Meeting on the Use of Isotopes and Radiationin Investigations of Fertilizer and Water Use Efficiency was convenedjointly by the Food and Agriculture Organization of the United Nationsand the International Atomic Energy Agency; the sessions were heldin Bangkok, Thailand, at the generous invitation of the Government ofThailand. Approximately thirtyfive participants from the countriesof Asia and the Far East presented papers or contributed to thediscussions.

The purpose of the meeting was to bring together, for the firsttime since the termination of the IAEA's six year co-ordinated ricefertilization programme, specialists in soil science and plant physiologyto discuss recent developments in the physiology, nutrition, and ferti-lization of rice; the programme also included reports by regionalscientists and lectures by authorities in areas other than rice; thisproceeding includes the 16 technical papers presented during the meeting.

While the informal study group atmosphere stimulated a full exchangeof experience and information on current developments in the applicationof isotopes and radiation to soil and crop production studies, a recordof these discussions has been excluded from these proceedings; however,the meeting's formal recommendations, which constitute a summary of th^discussions, are included; these focus on such areas as Rice, Other Crops,Soil Chemistry and Related Studies, Water and Funding.

OPENING ADDRESS

H.E. M.R. Chakratong TongyaiMinister of Agriculture ,Government of Thailand

21-25 April 1969

Honoured guests, distinguished Delegates, Ladies and Gentlemen?

It gives me great pleasure to be present at this opening session ofthe meeting of the Study Group on the Use of Isotopes and Radiation inInvestigations of Fertilizer and Water Use Efficiency.

If I recall correctly this is the third meeting sponsored by theJoint Division of the Pood and Agriculture Organization and the InternationalAtomic Energy Agency to be held in Bangkok. The first meeting for whichThailand had the honor of being the meeting place, was the panel meeting ofexperts on Induced Mutation of Rice Breeding in 1965. The second meeting,also held in 19&5* was on Rice Fertiliser Research using Isotopes.

It is indeed reassuring to know that atomic energy has been harnessedto serve useful purposes for mankind and, especially in the field ofagriculture, has resulted in more food so essential to human life, insteadof death and destruction as during World War II. On behalf of the Thaipeople, I wish to express to the two Jnited Nations Agencies, FAO and IAEA,our sincere appreciation for promoting the application of atomic energyfor peace in the field of agriculture.

We are all aware that, in many countries, tremendous advances havebeen made in the past fifteen years in research on fertilizer and water useby applying isotopes and radiation techniques. But, in most Asian countries,only a few scattered research projects have been carried out. Since fertilizerand water requirements vary with the soil, climacic condition and crop, first-hand knowledge is needed for each particular locality and for each crop.

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This meeting provides an opportunity for the exchange of experiencesamong Asian countries to help promote wider application of radio-isotopesand radiation techniques in fertilizer and water use researches in thispart of the world. From persone.1 acquaintance among scientists of variouscountries made during this meeting, I believe further "bilateral and multi-lateral contacts will be maintained in the future for the exchange ofideas and research results. All these will eventually lead to a betterand more exact knowledge of fertilizer uptake and water use for increasingthe crop yield and will result in the efficient application of inputs andresources to ensure increase in production and maximum profit for ourfarmers.

In this part of the world with the majority of the people engagedin agriculture and the future rapid growth in population, increase incrop production efficiency by maximum land and water utilization is'vitalto the solution of the food problem and to economic development.

Though crop production depends mainly on seed variety, soil fertility,protection, and cultural practice, soil fertility is the main factorin increasing the yield. Hence knowledge of proper and efficient applicationof fertilizers to tha crop.1 is extremely important for. the agriculturaldevelopment of our countries.

By further researches in the application of isotopes-and atomicenergy techniques, scientists will understand more of the nature andbehavior of nutrient elements in relation to various crops under variousenvironmental conditions 30 that they can advise farmers as to the kindand the amounts of fertilizer, and t3 3 time and the methods of applicationto various crops in various localities in order to ensure the effectiveand economical use of fertilizers and water.

Distinguished delegates, you are meeting here to share and exchangeknowledge among your colleagues, I hope that this meeting will give newimpetus to more intensive and extensive research in our countries. You may 'be sure that your contributions to the future development of agriculturewill benefit your fellow men.

On behalf of the Government of Thailand, I wish to extend a very warnswelcome to each and every one of you. May your stay in Thailand be pleasingand rewarding.

I wish you success in all your deliberations.- 2 -

OPENING ADDRESSD.A. RENNIE

Joint PAO/IAEA DIVISIONVIENNA, AUSTRIA.

Distinguished colleagues,

Public attention has "been drawn in various reports during the pastyear about the revolutionary developments in agricultural production andthe highly encouraging yield statistics, implying that the world foodcrisis may be approaching at least a partial solution. It is indeed truethat we may be on the verge of a break-through in agriculture production;years of patient activity in research are at last beginning to bear fruit.We are now able to say that there is real hope, given the right conditions,and providing the right steps are taken in the right sequence, that thefood situation can be transformed in areas such as.in Southern Asia fromone where the famine all too frequently stalked the land to where at leasta subsistence level can be guaranteed for all.

We must not, however, become complacent on the basis of the last fewyears' statistics on agricultural production. To relax our efforts inresearch, having just seen the major dividends that can arise out of sucheffort, could lead to the disaster that we have been struggling to avoid.It is of critical importance that those involved in research grasp thecomplexity of the challenge facing them.

It is for these reasons that the Agencies sponsoring this Study GroupMeeting, the International Atomic Energy Agency .and the Pood and AgricultureOrganization of the United Nations programmed this meeting. I takegreat pleasure on behalf of these sponsoring organizations to welcome you,I am sure that I put into words the feeling of all of you as well as thesponsoring organizations if I also at this time express our sinceregratitude to the Government of Thailand for having extended to us the kindinvitation to meet here in this ancient city of Bangkok and in our sparetime to bask in the beautiful surroundings of this fair city.

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I also want to extend to Dr. Sala Dasananda, Director General, RiceDepartment, his Conference Committee, and in particular, our hard-workingconference secretary, Mrs. Patoom Sanitwongse my sincere thanks andappreciation for looking after all local arrangements.

The Joint PAO/IAEA Division has "been instrumental in the past inholding Symposia, Panels, etc. at various localities throughout the world.This is the first Study Group Meeting that has been held, and we trust thatduring the next five days all in attendance will have an opportunity toenjoy and benefit from what might be termed "the informal study groupatmosphere", i.e. a full exchange of experience and information oncurrent developments in the application of isotopes and radiation to soiland crop production studies. You will recall that the.sponsoring

i.' -Organization supported under the IAEA's Research Contract Programme asix year co-ordinated rice fertilization study in twelve countries usingisotopioally labelled fertilizers. This Study Group is the :firstfollow-up to this programme and you will note that a significant portionof our discussions is devoted to the physiology, nutrition and fertilizationof rice. We trust that at the end of this Study Group Meeting .guidelinesas to the continued attention and support that should be given to theapplication of isotopic techniques in rice physiology and fertilizationstudies will be formalized. The tenth and eleventh sessions of the WorkingParty on Rice Soils Water and Fertiliser Practices of the International RiceCommission recommended active programmes in this area. We, in the Agency,await your recommendations.

Rice is not the only crop grown in the countries of Asia a'nd thePar East, and thus rightly, the programme includes reports offered byparticipants and lectures by acknowledged authorities in areas other,than rice. I trust you will find this portion of the programme, asstimulating as the initial lectures devoted to rice production.

And so, with this brief review of the scope of topics to be coveredin this Study Group Meeting I trust that all in attendance will find, inthis forum, an opportunity not only to further their knowledge but alsothrough the media of fruitful debate and discussion, leave these meetings

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"better armed with the tools that will enable each and everyone of us,on our return home, to more effectively attack the .problems restrictingyields of agricultural crops.

I wish you a most successful meeting and I herewith declare thisStudy Group Meeting on the Use of Isotopes and Radiation in Investigationsof Fertilizer and Water Use Efficiency formally opened.

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A Review of the Coordinated Research Programme onthe Application of Isotopes to Rice Fertilization

Studies, 1962-1968

By P. B. Vose

I. INTRODUCTION

The results of the Coordinated Research Programme were communicatedas they were obtained to the meetings of the Working Party on Rioe Soils,Water and Fertilizer Practices of the International Rioe Commission(Manila, 1964$ Lake Charles, 1966 and Kandy, 1968). The detailed resultsof the experiments have thus already been widely disseminated, and thepresent paper attempts to review in general terms the overall significanceof the programme; an appreciation of isotope techniques in fertilizerefficiency studies; some possible indications for the future.

For those who may not be familiar with the detailed organization,objectives and results of the programme, a summary report of the 6 yearsof work is available.

II. Research Achievements of the Programme

The broad research achievements of the programme can be brieflysummarised as follows:

(i) clearly defining the optimum conditions of placement ofphosphorus and nitrogen fertilizers;

(ii) clearly defining the relative efficiency of the majornitrogen sources;

(iii) achieving a better understanding of the effect of time ofapplication on the efficiency of nitrogen and phosphorus utilizationby rice ;

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(iv) obtaining "by direct measurement precise informationon the proportion of applied fertilizer actually takenup "by the crop;

(v) obtaining a clear - numerate - understanding of thepenalty paid in terms of fertilizer wastage, if inefficientplacement or incorrect nitrogen source is adopted?

(vi) demonstrating that "che basic factors concerned with theefficiency of fertilizer utilization by rice grown underlowland, i.e. flooded, conditions hold good for a verywide range of soil and geographic conditions, from Italy to Korea*

At the time the programme was started the lack of generallyaccepted theoretical and practical bases for the efficient nitrogenand phosphorus fertilization of rice was clearly indicated by thestandard texts, though Mitsui and his co-workers were pointing theway. Furthermore, the concept of efficient fertilizer utilizationi.e. the efficient uptake of the fertilizer by the crop, had not beengreatly stressed in those countries with long-established traditionsof fertilizer research. This was because in these developed countriesfertilizer is relatively cheap. However, in many developing countrieswhere rice is grown fertilizers are expensive and may require scarceforeign exchange.

How important is the need for efficient fertilizer use can be deducedfrom a study of the overall experimental results. Thus even under thebest conditions of nitrogen fertilizer application i.e* ammonium fertilizerploughed-in, the amount of fortilizev taken up by the rice crop seldomexceeds 50-35 per cent of that applied and is often less, even where thereis a significant yield response to 60 kg/ha of nitrogen. Under the worstpossible conditions, nitrate fertilizer applied at planting time, only5 per cent or less of the fertilizer applied is actually taken up by thecrop. Before the uso of isotope -techniques such estimates involved a largemeasure of guesswork. In the case of phosphorus about 5-10 per cent maybe utilized in the case of the most efficient - surface application -treatments, and as little as 2 per cent or less for depth or plantingpoint treatments.

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Efficiency of phosphate fertilizationIn general the very low efficiency of phosphorus fertilizers is

usually explained by the nature of the soil-fertilizer-interactions.The equilibrium concentration of the phosphorus in the soil solutionoften falls within the conoertration-limiiod part of the phosphorusuptake curve of the- crop. Thus the higher concentration of phosphorusaround the fertilizer particles may help explain the response tophosphorus application by the crop. Th?.s effect is of a temporarynature and the bulk of the phosphate gets eventually bovnd to thesolid soil complex, necessitating yearly applications of phosphorusfertilizer to maintain an e.d equate supply to the crop.

Comparatively little work had been carried out on fertilizerphosphorus placement for rice, and much of that was contradictory.The common custom, is to broadcast phosphate fertilizer, but the practicehad been based more on expediency than on facts. In India, early worksuggested that placement 2-5 inches below the plants was better thanbroadcast application, but a later series of experiments reported that 'broadcasting was superior to 3 and 6" daep placement. A Louisiana experimentindicated .that banding gave a consistently higher yield than broadcasting,"bur. studies in Texas showed no significant difference, between a series ofband and depth placements and broadcasting.

LLL Under lowland conditions, phosphate fertilizer applied on the., ratface or hoed int,o the top few cm of the soil ensures the most efficientutiliRp.tion of the fertilizer by the rice plant. Placement at planting pointv;,->,s ineffective.TrUning^ In general, phosphate application to the crop in one single dose attne tins of transplanting is at least as efficient as at other times. Latetiming and splitting up of phosphorus applications results in a slightinduction in the utilization of P from the fertilizer. The reduction isho?/3ver small and does not preclude later applications if the fertilizer isnot available at transplanting time. Nursery applications of phosphate donot result in either increased incorporation of phosphate in the plant orincrease in 'relative efficiency of latsr applications of fertilizer.

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K-P mixing and combined sources; Mixing ammonium sulphate and super-phosphate stimulates P uptake from fertilizer placed at a shallowdepth "but not on the surface. Phosphorus utilization was found to "belittle influenced "by the nitrogen component of combined N-P sources.Although placement of combined N-P sources at depth reduces theefficiency of P uptake, there is nevertheless an increase in P efficiencyobtained from the N-P mixing effect. This suggests that in practicethe application of a combined N-P source at a depth of 5 cm at transplantingtime gives nearly as efficient utilization of phosphorus as separateapplications of ammonium sulphate at 5 cm depth with superphosphate onthe surface.

Phosphate sources: Pot experiments carried out at the SeibersdorfLaboratory of I.A.E.A, compared natural phosphate fertilizers suchas Olinda, Araxa, Araxa Thermo, Tunis Rock, Florida Rock, Basic Slagand Bone Meal. It was found that on acid soils availability was generallyhigh, but that on alkaline soils only Araxa Thermo and Basic Slag had anavailability similar to superphosphate. In a comparison of commercialfertilizers it was found that K-metaphosphate + Magnesium Sulphate andK-orthophosphate were more available than superphosphate on all soil typestested. K-syrophosphate and K-metaphosphate were less available thansuperphosphate on all soil types. The striking effect of MgSO in increasingthe availability of P from K-metaphosphate remains unexplained.

Efficiency of nitrogen fertilizationConsideration of nitrogen placement and timing for rice must take into

account the peculiar physico-chemical properties of flooded soils and thetransformation of nitrogen compounds under these conditions. Thus in floodedpaddy soils there is an aerobic layer a few cm thick in contact with thewater and in this layer the processes are primarily oxidative. Below thislayer the conditions are anaerobic and reduction processes prevail.

The early Japanese work indicated that nitrification of ammonium nitrogenoccurred in the oxidising layer, resulting in its loss as nitrogen, butthat ammonium in the reduced zone is stable. Similarly, although nitrateis theoretically stable in the shallow oxidised layer, if it is leached

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into the reduced zone it is denitrified and lost as- gas"; Althouign~dTepplacement of ammonium was widely recommended in Japan, and successfulresults were .obtained in California and elsewhere, the value of thepractiae has not., been universally recognized. The broad geographic andedaphic scope of the present programme now permit a number of broadgeneralizations.

Placement t There is apparently never any penalty for placing ammoniumfertilizer at depth, nevertheless the generally beneficial effectsof depth placement vary according to soil type. The greatest benefitis obtained on acid soils of low organic matter content, and depthplacement is most essential on these soils, immediately followed bysoils of intermediate pH. With soils of low pH and high organic-mat'tear """~content the effect of shallow placement on the efficiency of N fertilizeruptake is only slightly higher than for surface placement. On soils withhigh pH containing Ca CO, the difference between surface and depth placementon the efficiency of N utilization is small or non-existent.

Although 5 ons depth placement of ammonium sulphate at transplanting timeusually increases the uptake of N from the fertilizer, compared withsurface application, 'no decrease in uptake of fertilizer N is found withplacement as deep as 15 cm. The optimum depth of placement may thereforebe greater than 5 orc» and there were small but not statistically significantindications to thi.s effect.

Timing> The late application of nitrogen as a. singTe"dose often.resultsin a very significant increase in the utilization of fertilizer^nitrogen, •-.There is little advantage in splitting the nitrogen betwee.n severalapplications - assuming that nitrogen is not very deficient. Exce.pt. wheresoil phosphorus is very deficient the timing of nitrogen application has no- •effect on the utilization of phosphorus. When soil phosphorus is very deficienthigher fertilizer phosphorus utilization may occur with late nitrogenapplications.

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Nitrate fertilizers are much more efficiently used when given as a latertop dressing than when applied at planting time. Under certain conditionsof medium pH with not too high organic matter content, top-dressing of allfertilizers may result in slightly more efficient utilization than applicationat planting time.

As far as investigated, a time 2 weeks "before primordial initiation appearsto "be the most appropriate time for a single top-dressing, and withammonium sulphate and urea applied at this time there is comparatively littledifference in effectiveness of utilization, compared with 5 cn> depthplacement at transplanting.

Sourcesi Ammonium sulphate and urea are about equal in effectiveness;sodium nitrate is very ineffective in supplying nitrogen to rice, whengiven as a "basic dressing at transplanting; under these conditions ammoniumnitrate is intermediate in value.

Comparison of Ammophos B and nitric phosphate with ammonium sulphateplus superphosphate showed that the efficiency of nitrogen utilizationfrom the two sources is about the same. Nitric phosphate is a much lessefficient supplier of nitrogen than either Ammophos B or ammonium sulphate.

III. Appreciation of the isotope technique for fertilizer utilizationefficiency studies

Fertilizer use efficiency can be studied by (i) direct measurement ofhow much of the fertilizer is taken up, by using isotopically labelledfertilizers,(ii) indirect measurement of the amounts of fertilizer taken upby calculating the difference between the yield of nutrient from a treatedplot and a non-fertilized control plot, (iii) indirectly, by observing yieldresponses to the various methods and times of fertilizer application.

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Why is the isotope method inherently superior? Why also is it notj • '

possible to get equivalent results from classical techniques usingyield or nutrient content as the criteria? The .basic advantage of the .isotope method is that the fertilizer actually taken up by the crop canbe detected and measured. It enables a straightforward quantitativecomparison of the amount of fertilizer element taken up for each experimentaltreatment.

It is well understood that under certain conditions yield techniquescan indeed be used to determine indirectly the efficiency of fertilizerutilization. This is particularly so on soils of extremely low fertilitywhere yield response to fertilizer is very high. However, the frequentabsence of consistent results where only yield response and the contentof a nutrient are used to compare placement, source and.time of fertilizerapplication is not hard to understand. As the yield of the varioustreatments of placement trials is usually approaching maximum and thedifferences are small the first requirement of such an experiment is thatthe levels of fertilizer application should be adjusted so that thetreatment responses are within the steep part of the yield response curve.In practice it is difficult to select such levels. Furthermore, on soilsof low fertility the results are confounded due to very marked increasesin root growth from fertilization - exploiting a larger volume of soil, henceacquiring more nutrients from the soil, changing the whole environment ofthe root and confusing the subsequent interpr§t.at.ip_n..o.£.fertilizer utilization.

Such yield experiments are necessarily- large to include several levelsof fertilizer application and to provide•adequate replication, and requirerepeating in a number of successive years. Such desiderata 'have seldom beenadequately met. The isotope procedure is valid for virtually every experimentregardless of soil or location, and the ability of the technique t& give inthe vast majority of oases a positive answer to the experimental objectives,is one of its .jnost valuable practical features.

The expense of labelled fertilizers has been put forward as an objectionto their use in field experiments. If a comparison is made merely of the costof labelled and unlabelled fertilizers this view has some validity. However,if the true cost of obtaining data of the same reliability from yieldtechniques if computed, i.e. the increased labour costs for carrying out

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the necessarily larger experiments and their need for repetition insuccessive years, then isotope techniques compare very favourable.

In fact, with the cost of N-15 at $100 per gram N-15 atom excess and anaverage cost for P-32 of $1.50.per me (plus preparation charge forsuperphosphate) there is no need for a properly designed field experimentto cost more than $100 for labelled fertilizer. This of course assumesthat labelled fertilizer is used in a subplot and unlabelled fertilizersare applied to the yield sub-plots.

Finally, isotope techniques are uniquely suited for determining the bestmethods of getting the fertilizer into the plant, i.e. for investigating themost efficient source, placement or time of application. They are notsuited for indicating the amount of fertilizer to appiy for optimum yield.When the most efficient means of application has been found then the optimumamount of fertiliser to use must be determined using normal commercialfertilizers.

The 6-year rice fertilization programme has surely given a cleardemonstration of the value of isotope techniques. The programme originatedin a desire to settle the differences of opinion as to the proper placementof phosphorus fertilizers this problem was in fact cleared up in the firstyear of the programme. In each subsequent year it was possible to attacka different problems showing both the economy of the technique and theadvantage of cooperative work.

IV Possible future work

Withi'i the context of the complete 6-year programme there are probalytwo areas of work which would repay further attention: the timing of nitrogenfertilizer applications and the confirmation of the work on placement andtiming with the new varieties. The 1964 experiments studied the time ofnitrogen application but it seems possible that efficient utilization might

occur from even later applications than were tried at that time. It isprobable that the existing results for N and P fertilizer placement andtiming are directly applicable to the new high yielding varieties.Nevertheless, these varieties have a considerably different growth habitand also a much higher fertilizer requirement than most of the varietieshitherto grown in the programme.

Sources: further work with slow-release nitrogen sources will berequired soon, though this will depend on the availability of materialsuitably labelled with N-15. From time to time further work with P sourcesmay be necessary but can be effectively carried out in pot experiments.

Also of value might be studies on the comparative nitrogen nutritionof japonioa and indioa varieties, particularly in relation to differentplant spacing of the latter. We need, too, -further knowledge of microelementproblems and the development and evaluation of foliar spray techniques.

... ' • - - - . . \»The objective of the programme was to study the most efficient.sources

and means of application, and in many countries it may now be appropriateto determine the best level of fertilizer application. Isotopes are notnecessary or suited to this work, nor is a co-ordinated approach, as theoptimum levels must be determined on a country by country or area by areabasis. '

The type of experimental work carried out in the programme and theprinciples on which it was based are equally suited to other crops:e.g. soybeans, sweet potato, pea-nut, cassava etc.

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Studies on the Efficiency of Time and Method of Fertilizer Applicationfor Rico Using K15 and P52

Mervyn W. Thenabadu

Central Agricultural Research Institute,Fere.clBri.iya, Ceylon.

Introduction

Oils of the "best joe'Irhcds fcr incieasing agricultural production is "bythe increased use of fertilisers. In Ceylon the use of moderate applicationsof fertilizers, particularly nitrogen and phosphorus, has resulted inappreciable yield responses with rice (l,2). It is also noteworthy thatthere has "been a steady inoreaco in fertilizer consumption .in Ceylonsince 1956 (3).

Good management practices, like placement of fertilizers and fertilizerapplications synchronised to meet the demands of the crop, are importantlor the efficient utilisation of fertilizers "by rice. The use of labelledr«rtilizevs has enabled studies en the efficiency of different fertilizers,r.ird on the time and method of applying fertilizers for rice.

Under, the Co-ordinated Contract Programme sponsored by the Joint PAD/IAEADivision of Atomic Energy in ?ood ir>d Agriculture, five experiments wereconducted in Ceylor be-'-T n IfM "-"d 196? to study the efficiency of timerind method of fe'ctiliz r application /or rice (4, 5, 6, 7, 8). This paper.juniiaarizes the results s,nd inclusions of these experiments.

Experimental

Experimental techniques were carried out according to instructionsfrom the Joint FAO/IAEA Division of Atomic Energy in Pood and Agriculture,Vienna, Austria. The details of procedure are described elsewhere(4, 5, 6, 7, 8).

The objectives of the experiments were as follows:

Experiment 1 (1964)To determine the efficiency of fertilizer nitrogen applied to lowland

ripe as affected "by time and rate of application using ammonium sulphatejand the efficiency of fertilizer phosphorus as affected "by time and rateof nitrogen application using superphosphate.

Experiment 2 (1965-66)To determine the efficiency of fertilizer nitrogen applied to lowland

rice as affected "by placement and the interaction with phosphorus placement}and the efficiency of fertilizer as affected "by placement and the inter-action with nitrogen placement.

Experiment 3 (1966)To compare the efficiency of different forms of nitrogenous fertilizers

as affected by shallow placement at transplanting and surface placementat primordial initiation; and to determine the efficiency of fertilizerphosphorus as affected by form and method of nitrogen application.

Experiment 4 (1966-67)To study the efficiency of utilization of ammonium sulphate by different

placement methods; and to study the interaction between nitrogen placementand the utilization of superphosphate, applied broadcast at transplanting.

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Experiment 5 (1967)To compare the efficiency of different combined nitrogen/phosphorus

sources wf bh ammonium sulphate plus superphosphate; and to compare theefficiency of different combined nitrogen/phosphorus sources as influencedby shallow placement at transplanting and surface placement -few> weeksbefore primordial initiation.

The first experiment was conducted at two locations viz: at theAgricultural Research Station, Maha Illuppallama and at the Central ResearchStation (Gannoruwa) Peradeniya. All the other experiments were conductedat the Agricultural Research Station, Maha Illuppallama.

Maha Illuppallama is situated in the dry zone of Ceylon which includesthe lowland plains of the north and east. The mean annual rainfall is1403 mm. The mean annual temperature is 27.3 C, (9)*

The soil at Maha Illuppallama where these experiments were conductedranges from sandy loam to sandy clay loam in texture and is slightly acidto neutral in reaction. The content of total nitrogen in this soil variesfronuO.09 to 0.15 percent while the content of available phosphorus (Olsen's)varies from 6.96 to 38.74 lb P2N per acre* The content of organic metterin this soil varies between 1.10 and 2.39 percent.

Gannoruwa is situated in the mid-country wet zone of Ceylon andreceives a mean annual rainfall of approximately 2131 mm. The mean .annual temperature is approximately 24.5°C, (9).

The soil at Gannoruwa where the first experiment was conducted is asandy clay loam which is moderately acid. The content of total nitrogenis 0.15 percent and that of available phosphorus (°lsen's) is 13.6 lbPgO_ per acre. The organic matter content of this soil is 2.30 percent.

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Results and Discussions

'• '*. . *From the results of the first experiment (Table I and II) which was

conducted in both the dry zone (Maha Illuppallama) and in the wet eone(Gannoruwa'; Peradeniya) by Nagarajah and Al-Abbas (4)» it was found thatthe greatest uptake of fertilizer nitrogen at both locations was from thetreatments where a single dose of 60 kg N/ha was applied two weeks beforeprimordial initiation. There was little advantage in applying this .nitrogen in two or three split doses. At the wet zone Station, (Gannoruwa,Peradeniya) it was ob'served that applying the fertilizer at transplantingor halfway between transplanting and two weeks before primordial initiationresulted in relatively less nitrogen being derived from fertilizer.byplants than when the fertilizer was applied two weeks before primordial

^ :.initiation. This could be due to loss of applied nitrogen from ,.the rootzone of plants especially since this station experienced a total of564.5 mm of rainfall during the first two months of the experiment(October and November 1964) in contrast to 280.1 mm at the dry zonestation during 'this period.'

At the wet zone station Gannoruwa, time of nitrogen application-had noeffect on the uptake of phosphorus from fertilizer, while at the dry aone

. •-. i ' 'station Maha Illuppallama a single application of nitrogenous fertilizertwo weeks after transplanting resulted in the most efficient uptake ofphosphorus from fertilizer by plants.•

The results of the second experiment conducted at Maha Illuppallama byNagarajah and Al-Abbas showed the benefits of deep placement of nitrogenon plant uptake (5). There was greater uptake of both nitrogen andphosphorus'by plants from fertilizers when ammonium sulphate was appliedin rows at a depth of 5 cm than when this fertilizer was applied in rows onthe surface (Table III). Placement of superphosphate or mixing with ammoniumsulphate did not influence the uptake of nitrogen by plants.

- 18 -

The results of the third experiment conducted at Maha Illuppallamaby Kathirgamathaiyah, Thenabadu and Al-Abbas (6) showed that there isgreater uptake of fertilizer nitrogen by plants when ammonium sulphate,urea, ammonium nitrate and sodium nitrate were "broadcast on the surfacetwo weeks "before primordial initiation than when they were applied inrows at a depth of 5 cm at transplanting (Table IV). These results arein agreement with those of the first experiment which was conducted attwo locations (4). It was found that plants absorbed the greatest amountof nitrogen from urea when applied at either stage. This was followedby ammonium sulphate, ammonium nitrate and sodium nitrate in descendingorder. The efficiency of the nitrate containing fertilizers was significantlygreater when applied as a top dressing than dressing at 5cm depth attransplanting.

The efficiency of phosphorus uptake by plants was highest when ureawas applied two weeks before primordial initiation.

Although there was increased uptake of nitrogen and phosphorus by plantswhich were fertilized with urea, there was no significant increase in grainyield as a consequence. The yields of plots that received nitratefertilizers were relatively lower than those of the other fertilizers. Amongthese plots, those that received top dressings of nitrate fertilizersyielded better than those that received basal application.

There was a highly significant correlation (r = 0.98l) between nitrogenderived from fertilizer in the straw and that in the grain at final harvest.If nitrogen in the grain is a indication of its protein content then timeof fertilizer nitrogen application could be a significant factor in improvingquality of rice although no significant quantitative effects due totreatments were observed.

- 19 -

The results of the fourth experiment conducted at Maha Illuppallaina byThenabadu, Jauffer and Willenberg revealed the benefits of deep placementof ammonium sulphate on grain yields of rice (7)« Sub-surface placementof this fertilizer at 5, 10 and 15 cm at transplanting producedsignificantly higher yields over surface applications, broadcast or inrows (Table V)..The highest yield was obtained when the fertilizer wasplaced 15 cm below the surface and the yield was lowest when fertilizerwas applied in rows on the surface. When fertilizer was placed at 16 cmdepth the yield .increase was intermediate. The yield responses to ammoniumsulphate treatments were generally associated with higher percentages' ofnitrogen derived from fertilizer and higher concentrations of the elementin the plants at 40 days from transplanting.

In this experiment the method of nitrogen application had no significanteffect on the percentage of phosphorus derived from fertilizer by plants oron the content of phosphorus in plants.

The efficiency of utilization of four combined nitrogen/phosphorussources as influenced by shallow placement at transplanting..and surface,placement two weeks before primordial initiation was. compared in the lastexperiment in the series, (8), conducted at Maha Illuppallama. .

Due to an error.in manufacture all treatments did not receive equivalentquantities of nitrogen (lO). The rates of application of the four nitrogensources were as follows*- Treatments A and E received 62.5 kg N/haj B..D,Eand H received 55-4 kg N/ha and C and G received 2J.9 Kg N/ha. The percentagenitrogen derived from fertilizer shown in Table VI are the corrected.percentages for the standard rate of 62.5 Kg N/ha calculated according ;to the A-Value transformation, assuming that the rate of soil nitrogensupply is not affected by the rate of the fertilizer. The highest percentageof fertilizer derived nitrogen in both grain and straw was found in plantsreceiving ammo-phos B which was applied in row at 5 cm depth at transplanting.

- 20 -

Where fertilizer was applied later (broadcast on the surface two weeks"before primordial initiation) ammonium sulphate and superphosphateresulted in the highest uptake of fertilizer derived nitrogen. The effectof treatments on percentage of phosphorus derived from fertilizerindicates that auano-phos B was the most efficient form of phosphorus.

Conclusions

The conclusions from these five experiments are as follows:

1. Deep placement of nitrogen at transplanting promotes "betterutilization of fertilizer "by plants than surface applications attransplanting. Placement at 15 cm is "better than shallower placementat 5 or 10 cm depth.

2. An application of nitrogen two weeks "before primordial initiationpromotes more efficient utilization of nitrogen than one at transplanting,although the former is a surface application and the latter is at a depthof 5 cm.

3. Nitrate containing fertilizers are not efficient sources of nitrogenfor rice grown under submergence.

4. The utilization of phosphorus by rice does not appear to be affectedby method of application of nitrogen.

References1. Ponnamperuma, F. N. "Fertilizer experiments in cultivators' fields in

Ceylon". Tropical Agriculturist, CXVI, (i960), 253.

2. Constable, D. H. "Fertilizer evaluation on rice in cultivators'fields in Ceylon". Research and Production of Rice in Ceylon. -Proc. Symp. of Ceylon Association for the Advancement of Science.D.V.W. Abeygunawardena (Ed). (1966),71 " The Colombo ApothecariesCo. Ltd. Colombo 2, Ceylon.

- 21 -

3. Kalpage P. S. C. P. "Fertilizer use on rice in Ceylon". Researchand Production of Rice in Ceylon. — Proc. Symp.of CeylonAssociation for the Advancement of Science.D. V. W. Abeygunawardena (Ed). (1966), 61,. The Colombo ApothecariesCo. Ltd. Colombo 2, Ceylon.

4. Nagarajah, S. and Al-Abbas, A.H. "Co-ordinated contract programme onthe application of isotopes and radiation in rice cultivationin Ceylon". Tropical Agriculturist, CXXI, (1965), 1.

5. Kagarajah, S. and Al-Abbas, A. H. "Nitrogen and phosphorus fertilizer15 32placement studies on rice using N and P "..

Tropical Agriculturist, CXXI, (1965), 89.

6. Kathirgamathaiyah, S., Thenabadu, M.W. and Al-Abbas, A. H."Utilization of nitrogen and phosphorus by rice as- affectedby form and time of application of fertilizer using N--and P52". Tropical Agriculturist, CXXIV, (1968), 1.

7. Thenabadu, M. W., Jauffer, M. M. M. and Willenberg, S. M."Studies on the placement of ammonium sulphate for lowlandrice using isotopically labelled fertilizers", -Tropical • .Agriculturist, (in Press).

8. Thenabadu, M. W., Jauffer, M. M. M. and Willenberg, S. M."Efficiency of combined nitrogen and phosphorus sources forrice as influenced by time and method of application(Unpublished data).

9. Mueller-Dombois, P., "Climate Map of Ceylon. (1968). •Smithsonian Ecology. Project, Department of Botany,University of Ceylon, Peradeniya, Ceylon.

10. Vose, P. B. (1968). Personal communication.

- 22 -

Table I - Effect \f time !iii;?fiS.ll -CJL. --e'•'• and- •bt£1 .gpjLgf.Nitrogen and Phosj>horus Utilization by P.ice Plants. (Experiment 1 - Maha Illuppallama)

Nagai

Treatments* Grain YieldKg. N/ha. at times Kg -./ha.

a

60003030020

L. S.I... S.

b

060if3003020D. atD. at

c

006003030205 % level1 % level

3141299829633136343731113003663887

•ajah and Al-Abbas. 1964 (4)

Percentage- ft derived

fromfertilizerby plants32.128.235.131.731.532.528.8n.s.-

Nitrogenin .plants

1.301.561.671.221.741.451.380.29-

PercentageP derivedfrom

fertilizerby plants39.746.433.842.343.339-7^35-87.910.6

Phosphorusin plants

0.1910.1890.1950.1870.1930.1900.201n.s.-

and 60 Kg. KgO/ha. as superphosphate and muriate of* All plots received 60 Kg. ?20 /ha.potash respectively,a s> Time > at transplanting.b = Time, halfway between the time of transplanting and two weeks before primordial initiation.

Prinordial initiation is defined as the time the ear can first be felt at the base of the shoot.c = Time, two weeks before primordial initiation.

Table II - Effect of Time and Rate of Application of Ammonium Sulphate on Yield and Efficiency of

iro

Nitrogen and Phosphorus Utilization by Rice Plants. (Experiment 1 - Gannoruwa}Nagarajah and Al-Abbas, 1964 (4)

• «Treatnents* Grain Yield

Kg.w/na« a-t times Kg. /ha.a b c .,

60 0 00 60 00 0 6030 30 o30 0 300 30 300 20 20

L. o. D. at-£> $•L. 8. D. at l.fo

... ........... . ........._

v •»

. 4291391142964291363443364410

-level 713 • -• •-level 953

* All plotB-rwelved €0 Kg.' P_0-/haV'respectively.a = Time, atb a Time, ha]

transplanting;fway"b"e~tween the time

PercentageN derivedfrom

- fertilizerby plants

13.820.827.418.723.224.125.47.710.3

and 60 Kg. K /

i of transplant!

Nitrogenin plantsw

.

1.882.012.352.091.992.351.990.29•»

Percentage PhosphorusP derived in plantsfrom - (<£\

. fertilizer" by plants

20.421.830.021.929.723.926.7n.s.—

ha. as superphosphate and muriate

ne and two weeiks before orimordia]

- ...

0.1720.1680.1500.1610.1580-.1740.133n.s.—

of potash

L initiation.Primordial initiation is defined as the time the ear can first be felt at the base of the shoot,Time, two weeks before primordial initiation.

Table III - Effect of Fertilizer Placement on Yield and Efficiency of Nitrogen and Phosphorus

ro

Utilization "by Rice PlantsNagarajah and Al -Abbas,

T r e a t m e n t . s GrainN Yield

Fertilizer Fertilizer. Fertilisers mixed .... /,. or separate Kg./ha.

In rows on In rows on. Fertilizers mixed 6073the surface the surface before applicationIn rows on In rows on Fertilizer applied 6688the surface the surface separately in rowsIn rows at In rows on- Fertilizers applied 66925 cm depth the surface separately in rowsIn rows at In rows at . Fertilizers mixed 66115 cm depth 5 om depth before applicationIn rows at In rows at Fertilizers applied 67055 cm depth 5 cm depth separately in rowsThe N ahdP Fertilizers mixed, broadcast on 6542the surface and mixed into the top 5 cm ofsoil (puddled)

L.S.D. at 5 $ level 537L.S.D. at 1 level 721

(Experiment1965/66 (5)

$age Nderivedfromfertilizerby plants18.2

20.6

31.2

55.9

31.6

19.4

6.28.4

31

Nitrogeninplants ($)

2,59

2.77

2.81

2.96

2.76

2.59

n.s.

$age Pderivedfrom

. fertilizerby plants38.9

37.1

49.7

50.3

37.750.8

9.913.3

Phosphorus'inplants(ft

0.189

0.185

0.1970.215:.201

0.198

n.s.

NOTEi All tieatments received 60 Kg.N/ha. 60 Kg. PgC /ha. and 60 Kg KpO/ha. as Ammonium Sulphate,Superjhosphate and Muriate of Potash respectively.

(60 Kg./ha. = 53.52 Its/acre)

Table IV - Effect of Form and Time of Application of Fertilizer Nitrocen on Yield, and isff-io-ior,™of Nitrogen and Phosphorus: Kathirgamathaiyah,

UtilizationThenabadu and

by Rice Plants (Experiment ^Al -Abbas, 1966 (6}

GrainT r e a t m e n t s - , Yield

Kg/ha.

'.* • e

Ammcniusa sulphate at transplanting . 6621in rows at 5 cm depthUrea at transplanting in rows at 71405 cm depth

ra Ammonium nitrate at transplanting 5917*p in rows at 5 cm depth

Sodium nitrate at transplanting 5961in rows at 5 cm de'pthAmmonium sulfhate at 2 weeks before 7212primordial iritiation broadcast onthe surface ~" — " ... -Urea at 2 weeks before primordial 6834initiation bioadcast on the surfaceAmmonium nitrate at 2 -weeks before 6742primordial iritiation broadcast onthe surface- ...... ...._.„...._Sodium nitrale at 2 weeks before 6108primordial iritiation broadcaston the surface

L.S.D. at 5 $_leveL - 63.8 . ... -L.S.D. at 1 % level 859

Percentage N derivedfrom fertilizer atmaturityStraw

17.0

18.8

8.9

3.6

19.0

22.4

13.6

9.8

: 3.3

Grain

17.2

20.2

8.4

4.5 ..19.0

24.8

12.8

6.9

Percentage.? derived .fromfertilizer by plants (Straw)2 weeks before At primordialprimordial initiationinitiation21.2 19.1

16.2 16.3

19.7 18.4

18.1 16.8

19.8

•me rare or nitrogen was 60 Kg.W/ha,All trratments received 60 Kg.PgO /ha. and 60 Kg.K?0/ha. as Superphosphate and Muriate of Potashrespectively, broadcast on the surface at transplanting.

Y - Effect of Ammonium Sulphate Placement on Yield, and Efficiency of Nitrogen and PhosphorusUtilization by Rice Plants (Experiment 4)Thenabadu, Jauffer and Willenberg 1966-67 (7)

T r e a t m eN-Fertilizer

Broadcast onthe surface

In rows on tisurfaceIn rows at fcm depthIn rows at 1Ccm depthIn rows at 13cm depth

L.£

n t s Grain YieldP-Fertilizer **'

Applied at trans-planting broadcastoh the surface

e - do -

- do -

- do -

- do - *

.D. at 1 $ level

/ha

5233 a*

4652 a

5956 b

6061 b

6555 b

Percentage Nderived fromfertilizerby plants**54.7

49.0

54.565.0

67.9

13.8

Nitrogenin plants**

?oA\7>)

2.68

2.77

3.30

2.98

3.440.68

PercentageP derivedfrom Fertilizerby plants**71.1

72.6

71.6

75.1

67.8

n.s.

_Phosphorusin plants

0.135

0.186

C.189

0.185

0.197n.s.

* Duncan's iultiple Range Test at 5 i° level of significance.Means not "followed by same letter are significantly different from each other.

** Plants sanpled 40 days after transplanting.NOTE't The rate of nitrogen was 60 Kg,/ha.

All treatments received 60 Kg.P2o5/ha. and 60 Kg.KgO/ha. as Superphosphate and liariateof Potash respectively, broadcast on the surface at -transplanting.

Table VI - Effect of Separate and Combined Sources of Nitrogen and Phosphorus on Yield and Efficiency ofNitrogen and Phosphorus Utilization by Rice Plants as Affected by Method of Application (Experiment 5)

Thenabadu, Jauffer and Willenberg, 1967 (8)

T r e a t m e n t sN-Fertilizer P-Fertilizer

Percentage N derivedfrom fertilizer atmaturity________

Straw Grain

Percentage Pderived fromfertilizer atPrimordialInitiation

P in plants ($)at PrimordialInitiation

A-Ammonium Sulphateat transplanting inrows at c cm depthB-Ammo-phos B, attransplanting inrows at 5 cm depthC-Nitric Phosphate(75 $ soluble?) attransplanting in rowsat 5 cm depthD-Nitric Phosphate(25$ soluble P) attransplanting inrows at 5 O|B depthE-Amronium .sulphate,2weeks before P.I.stage,

"L.")21.20

- do -

- do: -

Superphosphate at 14.702 weeks before

broadcast on the surface P. I. stage, broad-;. - . cast on the surfaceP-Ammopfeoa B>at 2 Phosphate applied 12.45.weeks before P.I. stage combined with Nbroadcast on the surfaceG-Nitric photphate (75 - do -soluble ?) at 2 weeksbefore P.I.stage, broad-cast on the -rurfaceH-Nitrio phosphate (25 - do ••—

17 02Superphosphateat .transplantingbroadcast on thesurfacePhosphate applied 55.39 24.77combined with N

15.55

10.49 15.33

18.32

15.45

10.09 7.28

10.37 9.09

37.4.

44.8

3-6.2

35.1

25.4

28.7

18.6

soluble P)at 2 weeks before P.I.stage, broadcast on the surface17.4

0.208

0.183

0.213

0.193

0.213

0.229

0.245

0.218

STUDIES ON THE COMPARATIVE NUTRIENT REQUIREMENTSOP LOW AND HIGH YIELDING VARIETIES OF RICE

A.B. Khan, L. RahmanS.I. Chowdhury, S.M. AlamP.K. Deb and Y. All

Atomic Energy Centre, Dacca, East Pakistan

ABSTRACT?A series of glass house and field experiments on nutrition and

physiology of rice were conducted with or without the application ofradioisotopes. This paper -contains information, in a summarised form,covering the significantly important aspects of the research findings.

Analytical data of various grain and straw samples of rice, collectedfrom fields revealed that grain N, P and K contents of different kinds ofrice are in the decreasing order of Boro (Summer rice), Aman (Winter rice),Aus (Autum rice) and for Ca content, the order is Aus, Boro, Aman. Ausstraw contains more P, K and Ca than Aman and Boro straw, in Boro strawthe N content is the highest.

•xpPlacement of P' labelled superphosphate at various depth and withcontinuous and intermittent flooding did show variation in the uptake anddrymatter yield. Absence of fertilizer K apparently reduces the uptake of

32N from urea source but much from ammonium sulphate. Uptake of P wasmore when N was applied as urea than as ammonium sulphate.

Low yielding local Aman rice (Naizersail) does not respond beyond thedose of 60 Ibs N/acre while high yielding IRRI variety (IR8-288-5) showedprogressive increase of yield up to 180 Ibs.

Chlorophyll a and b content of leaf increased with higher N applicationupto 90 Ibs N/acre in local and 120 Ibs N/acre in IRRI varieties and withmore chlorophyll in IRRI.

Crop logging (5rd leaf analysis at 65 days) showed nearly maximumN content in local varieties with 60 Ibs N/acre application while that ofIRRI increased progressively up4;o 240 Ibs N/acre.

- 29 -

N, P and K content of low yielding varieties, are 2.2, 0.2 and 2.0 $while those of high yielding varieties are 2.5, 0.25 and 2.5 $ respectively.Analytical data of 25 day old leaves may "be used as an index forcorrecting the deficiency level of nutrients for ultimate higher yield.

In Boro season "both low and high yielding varieties showed increasedN and K uptake with higher rates of applied fertilizers, more progressivebeing with IEBI varieties. For IBRI, grain yield and N content was moreand P content was less in Boro season than those in Aroan season, K-contentremaining same.

In IRRI (Aman) leaf Ca-content (3rd leaf at 65 days) decreased verysharply and consistently with increased N-applioation, "but -that was notapplicable with local varieties.

59Total and applied Fe^ content of rice plants was more at earlierstages (JO days) in IRRI than in Naizersail (local); but at. ..later stage

t •the Fe-concentration increases in the local variety, both from foliarspray and soil application. Plant Hn concentration increases with higherdoses, more being in local varieties, than in IRRI. Higher concentrationof Fe and Mn reduced D.M. yield.

- 30 - ..

Introduction*World population is increasing at a fantastic rate and the

Agricultural Scientists are putting their efforts to meet the foodsituation created "by over population. Naturally, the ultimate aim ofthe workers in all fields is to produce more and more food "by betterfertilisation, cultural practices, introduction or evolution of newvarieties and controlling pests and diseases. Agricultural practicesadopted in a country or region, based on the existing varieties of acrop do not usually hold good for the newly introduced or evolved varieties,having the capability of higher productivity. Rice, a major cereal cropis grown in varied climatic, topographical and soil conditions. Keepingthis in view, an attempt will be made in this paper to discuss thefertilizer requirement of low and high yielding varieties only.

The requirement of various nutrients by rice plants depends on thevariety, soil condition, yield-target, seasonal variation, culturalpractices and many other interrelated factors- JJo...variety,, low or .highyielding, is likely to produce the maximum unless it does or can absorband assimilate the optimum nutrients either from the soil or from theapplied fertilizers. The Japanese agricultural scientists are presentlyaiming to produce 50 % more yield from a: unit area than what they areproducing now. In order to obtain a target yield from the high yieldingvarieties, the scientists are working to find out the optimum fertilizerrate, instead of seeking the yield-target by increasing the rates.

Islam (1965) reported -chat 50-100 % yield increase of rice can beachieved only by applying fertilizers. But for judicious application, onemust know the varietal characteristic in respect of nutrient absorptioncapacity and yield of that strain. Standard fertilizer recommendations forcommon East Pakistan varieties are about half of those used for the highyielding IRRI or Japonica varieties.

Over 10 tons/ha of rice was produced in Japan by applyingN P K § of approximately 200, 150, 250 kg/ha in a loamy soil (1966).Karim et.al (1968) found that application of lime in the acid soilsof Savar and Tongi, Dacca 8 equivalent to 6095 and 40$ lime saturationshowed 2&fo and 2jfo yield increase. The changes in pH were from 4.8 to6.5 and 5.0 to 6.5 at Savar and Tongi, respectively. It is likely thatCa also served as a nutrient other than a soil amendment.

The problem of micronutrient is also important when high yieldingvarieties are cultivated with higher rates of fertilizer, under floodedcondition on acid and calcareous soils. Tanaka (1966), reported remedialmeasure of iron toxicity by applying manganese to a certain extent.

It is, therefore, apparent that cultivation of high yielding ricevarieties needs closer attention from all corners, keeping in viewthe factors prevailing in the region they are grown.

SHORT DESCRIPTION OF THE EXPERIMENTS:Experiment Ho. 1Nutrient uptake by mature rice crops.

In order to assess the loss of some major nutrients (N,P,K and Ca)from the soils of East Pakistan by cropping, plant samples of Rice, Juteand Sugarcane were collected from various places and analysed. The analyticaldata of rice straw and grain revealed some very valuable information abouttheir nutrient contents. The table given below will show the exact positionin this respect. The other crops are not considered here.

- 32 -

Table - 1

Chemical composition of unhusked grain and straw.

Type of rice S$ P$ K$ Ca$

Aus (Autumn).GrainStraw

Aman (Winter)GrainStraw

Boro (Summer)GrainStraw

0.980.58

1.250.58

1.40•--- 0.90

0.250.10

0.290.04

0.320.08 •

0.321.55

'0.431.09

0.531.5-3 - '

0.220.41

"O.O?6.31

0.090.19

Result and discussion»•(Prom the above table it may "be inferred- that Boro grains contain more

nutrients (N, P, K) than either Aus or Aman grains while the Ca 'contentis the highest in Aus grains. In Aus straw, P, K and Ca contents were morethan those in Aman and Boro varieties; but the N-content was the highestin Boro. This provides one with the opportunities to think.that .differenthigh yielding varieties of IRRI grown in East Pakistan in all the threeseasons will require variable rates of fertiliser depending on the cropseason.

> . .'

Experiment No. 2Effect of continuous and intermittent flooding on.the uptake of appliedphosphorus by rice plants._______________________________'

Red soils of Dacca (pH-5.5 to 6.0) collected in layers of 0-10,10-20 and 20-25 cm deep, were used in pots for experiments under 'continuousand intermittent flooding. In one series the soils were placed layer by layer

- 33 -

and in another they were mixed. Superphosphate was placed on the surface, at10 cm depth "before transplanting, rate in all oases "being 80 Ibs P20 /acre,except the control. Rice plants, harvested at an interval of 20 days fromtransplanting, were analysed. Data are given in Table-2.

Result and discussiont32• Dry matter yield, grain yield, 7 uptake were the highest with

surface ajpplication. Mixing or non-mixing of soils had little difference ondry matter yield and grain production, "but uptake of P O,. was more from surfaced 5application on mixed soils than on non-mixed.

Experiment No. 2"Effect of continuous and intermittent flooding on the

uptake of applied phosphorus by rice plants".

Table shows dry matter, straw and grain yield in gm and phosphoruscontent in mg (underlined) per pot of 3 hills.

Treatments

$|Control

Conti- 5 Surf acenuous f.F!oo- *axn* flO on 1

y depth

OControlInter- -K ———————mitt- Or, *„.»+ ^Surface

X•f", or,- J)

d?ng, jKo cmIdepth '•

Mixed soil

D.M.1stcutt.

2.331

i 3.04I 6.24————| 2.94

0.88

2.49

2.824.77

2.572.06

D.M.2ndcutt.

7.32}

10.8822.40

7.825.16

6.61

9.8415.65

1 7.93.6.27

1Straw

'

17.74

23.2814.63

25.546.27

13.36

13.77 I5. 8 j

Grain

12.96

Non-mix«d soil

D.M.1stcutt.

2.20

17.65 j 3.0821.67 | 6.07

15.205.82

8.87 '

10.5311-95

14.39 - I 10.443.56 j 8.15 'i ——

3.03400

D.M. |2nd } Straw°utt. (j

7.65

9.5316.04

10.6713.85

2.10 J 6.01

2.37 fi 9.204.41 |l4.Q9

-'2. 84? 8.503.006 9.15—— t —— *• J

20.34

25.2912.13

20.906.88

14.94

13 ..305.65

.14.49i-22 •

Grain

14.69

16.34!2±!1

15.498.61

8.53

11.5912.73•i • i- ' ~-

11.188.71

- 34 -

Experiment No* 3

The effect of rates and forms of nitrogen fertilizers on the uptakeof P and N by rice plants.______________________________

A glass house experiment with red soil of Dacca applying 40 Itsand 80 Its N/acre, separately from ammonium sulphate (A/S) andurea was conducted to study their effect on the uptake of P and Nand also the yield. Two levels each (o and 40 Ibs/acre) of P 0_and KgO were applied with both the forms of nitrogen. Three hillswas harvested, at 50 days after transplanting, for analyses andthe remaining 3 hills at maturity.

Results and discussion

Table-3 shows that P and K influenced D. M. and grain yield.32Uptake of P increased when N was applied as urea than when as

ammonium sulphate. Subsequently, a field trial on lateritic soilsof Savar, Dacca was conducted, using 2 sources of nitrogen at threelevels (0,40 and'80 Ibs N/acre) with basic phosphorus and potassium(60 Ibs/acre of P20 and K20). Data showed that 80 Ibs N/acre as ureawassuperior to A/S in acid soils, 'producing 32$ and e$0 more yieldover the control (NQ) respectively. With lower N rates, both sourceswere equally effective. It can reasonably be expected that high yieldingvarieties may be difficult to grow on acid soils with higher ratesof A/S.

- 35 -

Table - 3Experiment No. 3

"Effect of rates and forms of nitrogen fertilizers ,onthe uptake of phosphorus and nitrogen by rice plants"____________(glass house experiments^________

Table shows yield of dry matter, grain_in gm and..FQr.t.TP a.ndtotal-N in mg per pot (three hiUs).

Treatmentsin Ibs/acre

Control

AmmonSulphate

>i

Urea

W4o .WoN0P40K40N40P0K40

WoN40P40K40H80P0*40N80P40K0W80P40K40

N40P0K40

W40K0N40P40K40N80P0K40N80P40K0N80P40K40 {

D.M. .1st harvestin gm

. .0*701.11

1.23

1.36

1.77 ' .2,311.992.98

3.27

1.20

1.61

1.911.832.112.39 ,

Grainyieldin gm

2.45

2.22

3.02

2.27

2.56

2.84

2.68

1.07

2.0y

2.532.51

3-372.853.162.57

Fert-Pin mg

.•

0.530.68-

0.81 .1.04"

• ' -

0.831.01

-

0.92

1.30-1.22

1.15

Total-Nin mg

3.07

5.62

6.16•— -~-g— ---•

8.7712.68

13.4518.19

14.55

7.90

7.84

9.44

15.4910.6110.95

N.B. Straw: Grain Rations - Control - 1.66, A/S - 2.50, Urea - 1.75,- 36 -

Experiment No. 4 ......

A comparative study of local Aman and IREI varieties on theirH-tQleranoe and yield, with or without potassium.________

Standard recommendation of the Department of Agriculture,East Pakistan is 40-40-40 Its/acre of N, PgO and K^O. It isassumed that if "balanced P and K fertilizers are applied with N,even the local varieties can absorb and assimilate more nitrogenand yield more grain to a certain extent. The intention was alsoto study the performance of newly introduced IRRI varieties, wellknown for iheir high nitrogen absorption capacity, with more grainyield.

The Aman experiment was carried out on red soil of Tongi,Ite'jca, based on :the information obtained through the earlier isotopioaxp3riments. Latisail (local),and IRQ (high yielding) varieties weretested with 60, 80, 120 and 160 Ibs N/acre for local and 60, 120,180 and 240 Ibs N/acre for IRRI. The rate of potash was .0,60,120 Ibs/acrof K«0 and P2°c was applied § 80 Ibs/acre. N as urea was applied inthree splits viz. - at transplanting, 25 days and 50 days after trans-planting. Sufficient irrigation was provided as and when needed.

P.nsults and discussion;Field and analytical data are given in Table-4 and 5 for Latisail

and IR8, respectively. It is observed that Latisail produced the highestyi3ld with 60-80-60 Ibs/acie rates of N, P-0,. and K«0 respectively. Theresult confirm some of our earlier findings and nullifies the idea thatlocal varieties cannot stand higher rates of N and produce good yield.Nitrogen beyond 60 Ibs N/acre did neither increase yield nor the plantIT-content of the local variety appreciably or proportionably, indicatinglimited requirement of the variety. Such N rates induced more lodging withloss of yield.

- 37 -

The highest yield of IR8 was obtained with 240-80-60 rate anda reasonably high yield with 180-80-0 or 180-80-80 rates. Potash hadno effect on yield, probably due to the sufficient soil K content.Nitrogen content of IR8 increased upto 240 Ibs N/acre rate of application.

Leaf N, P, K content of 65 days old plants were 2.2, 0.2 and 2.0$for local and 2.5, 0.25 and 2.5$ for THRI varieties and these levels areconsidered to be adequate. However, it is also expected that the N, P, Kcontent of whole plant at about 25 days may serve as an index for correctingthe deficiency, if any, on the standing crops.

Leaf samples from 65 days old plant showed that both in localand IRRI varieties, the Ca content progressively decreased with higherrates of N application;. ov»n with liming §0.35 ton/acre. The reductionwas sharp in case of IHRI J;han in local varieties. Treatment with nonitrogen had 0.15$ plant Ca which went down to 0.08$ with 180 Ibs N/acrefor IRRI and that for Latisail v/ent down from 0.11$ to 0.10$. This maybe from the shortage of soil Ca~supply and the dilution effect due to moredry matter production. However, the competition between N H* and Cationscan not be ruled out. Karimet alfound increased Ca uptake and yield due tohigher rate of liming in acidic rice field .

Table - 4

"Effect of higher levels of Nitrogen with and withoutPotassium on nutrient content and grain yield of T.Aman rice (Latisail) grown at Tongi, Dacca".

treatments % 25 - day . plant . jIbs/acreN60K0

»*ftoN60K120N80K0vr irNftOK60W VW80K120N120K0N120K60

N120K120

»6oKo 1

N160K60N160K120

N% 0 P% 0 K% i(

1.90

1.90

1.89

1.851.80

1,27

2.031.48

1.322.02

"l.34

1.99

1 65 days 3rd leaf j1 N$

0.2? | - 0 2.311 —— — f —— *0.300.27

0.23

0.27

0.23

0.29—————0.30

0.30

0.27

0.27

0.29

¥ ————— '•1.38 |" 2.23 :2.03 0 2.371.70

2.152.10

1.83

1

2.052.22

2.18

2.31- —— — i ————— •2.03 j 2.39y . i2.15 I 2.42— —

2.65 '

2.27'

2.20 | 2.42

1 F?° <0.17

; 0.22 <i 0,17

I °'14<1 0.22 ,

i °-171 ii 0.19* (I 0.19r "" •i 0.15j 0.19)| 0.15 ,

0.19;

) B6 (Grain yieldIbs/acre

I 1.98 8 3374"i —— rt ———— : ————I 2.78 | "3539i 2.50 5 3210

2.25 | 29631.90 (j 3045

/ } .! 1.90 3210

I 1.581.38

! 2.05

1.65«

i 2.17

3374

3210

3045

33743210

v . ...| 2.38 | 2880

1. Replicates were composited for plant analysis.2« A-basal rate of 80 Its PgO /acre was applied in all the plots. N and K

were calculated as N and KLO respectively. Fertilizer used were urea,triple super phosphate and muriate of potash.

- 39 -

Table - 5

"Effect of higher levels of Nitrogen with and without*

Potassium on nutrient content and grain yield of T.Aman rice (IR8-288-3) grown at Tongi, Dacca".

TreatmentsIbs/aoreN60K0N60K60N60K120N120K0N120K60N120K120N180K0N180K60N180K120N240K0N240K60 ...N240K120

25N?61.341.62

1.51

1.441.68

1.66

1.61™ ~ ™ —

1.561.66

1.86

1.77

1.53

days plant 1 65 days 3rd leaf» P% J) K$ P Wfc 0 P^ 1

0.37 2.03

0.40 2.20,

0.39 i 2.10

0.42

0.45

0.46

0.40

0.48

0.450.46

0.53

0.49

1.982.20

2.332.032.20

2.20

2.03

1.60

2.10

2.02

2.22

2.052.48

2.53—————

2.25

2.861 ———2.892.72

3.05

2.09

3.02

0.19

0.21

Kf51.78

Grain yield1 bs/acre3127

2.10 ! 2963

0.20- j 2.05

0.26.

0.28

0.25 ,

0.28

0.300.33

0.34

0.29

0.31

2.58

2.702.052.582.43

2880

3374

3374

33743621

5621

2.63 : 33742.98 I 37032.63 j 38681.80 3457

Replicates were composited for plant analysis.

- 40 -

Experiment No.. 3

Response of high and low yielding Bororice to higher nitrogen rates.____ .

This experiment was conducted in Boro season at Mirpur, Dacca,with the same idea and objective as that in Aman season, except withslight changes in the fertilizer rates for the low yielding local variety.For IR8, th« fertilizer rates were 60, 120, 180 and 240 Ibs N/acre incombination with 0, 60 and 120 Ibs KpO/acre. For Habiganj-VIII the rates ofN were 60, 90 and 120 Ibs/acre, K-treatments remaining the same. The basicrate of Pp c was ^ Ibs/acre from superphosphate.

After 65 days of transplanting, third leaves were analysed for N, Pand K contents.

Results and discussionsThe analytical data and grain yield are shown in Table-6. Highest

grain yield was recorded with 120-80-60 treatment in case of IR8 whileHe/biganj-VIII responded more or less equally to all N-treatments, irrespective01" K-application. With no decrease in yield due to more vegetative growthout of higher N-rates it may be observed with interest that if properlybalanced, even the local varieties can stand upto 120 Ibs N/acre. This•';rend was also observed in case of local Aman varieties.

Nitrogen application increased leaf N-content of IR8 almostconsistaatly with increased rates. In the low yielding variety N aloneincreased the leaf N-oontentj but the difference was not pronounced.

If the leaf N-contents of plants grown in Aman and Boro seasons arecompared, it may be observed that N-contents was 40$ higher in Boro seasonresulting proportionately higher yield. Potash application was ineffectivei<i respect of both K-content and yield, probably due to high soil K-status.Higher N-uptake may be mainly due to more solar radiation during clearsunny season, compared to cloudy monsoon season (University of Philippine -1967). It may be concluded that unless leaf N-content can attain the levelof 3«5$ in IRRI varieties maximum yield cannot be obtained.

- 41 -

It may also "be mentioned here that the concentration of chlorophylla and to in leaf increased with higher rates of N-application upto90 Ibs.IT/acre in local and upto 120 Its N/acre in IRRI varieties.However, the concentration of both a and "b were more in case of highyielder.

Application of K tended to increase the chlorophyll concentrationin low yielding varieties while it caused reduction, in high yieldingvariety upto the level of 120 Ibs N/acre application, with again anincreasing tendency at higher levels.

- 42 -

i'aole - 6

Experiment No. 5"Response of high and low yielding Boro rice to highernitrogen rates (Varietys IRRI-8 and Habiganj - VIII)"

Treatments Nutrient contents of 65 days' old leaves and yield of grainin Its/acrein Acs/acre

i

N60K0N60K601I60K120*90K0N90K60N90K120N120K0N120K60H120K120N180K0N180K60N180K120N240K0N240K60N240K120

IRRI - 8 ' Habiganj - VIIIN#

2.922.872.57---3.463.203.543.48 ;3.603.553.42 ;3.483.82 |

P#0.240.220.26---0.230.27 i0.240.260.260.240.240.240.24

K$2.502.372.85---2.302.372.422.502.432.782.302.432.53

Its/aciB478949614690- •-

.4551522350025215

' 51995109480541244485

1 n£2.982.843.153.023.312.933.332.685.25 !

*'0.290.300.360.380.340.330.350.290.34

K$2.402.232.382.402.55 12.52 I2.603.102.50

Its/acre328834363387331333783469341134693674

- 43 -

Experiment No. 6

Effect of Fe and Mn application on the D.M. yield,Fe and Mn contents of local and IRRI rice._____

Pe and Mh5 were used in a pot culture experiment to study theirnutritional behaviour on two varieties of rice namely, "IR-8 and Naizersail.T-he mode of application -of the nutrients were foliar spray and soilapplication with various concentrations' (Tables 7 and 8) having vje-foldreplications. An alkaline soil (pTJ-7*.4) was used for the experiment. Five weeksold seedling, 4 .per pot were transplanted. Plant samples were collected and ana-lysed -at the stages - 30 and 60 days aftefr transplanting. '

lUsult and discussion:Columns 4 and 10 of Table-7 show that Fe content of JO days IRRI

plant samples is more than those of Naizersail, but at later stage theconcentration of Fe in the local variety increased" due to both type ofapplications. It appears that in general, total Fe concentration slightlydecreased beyond the dose of 15 p.p.m. in both varieties with the foliar"spray whereas the concentration increased from soil application.

Both total and applied Mn concentration in plant increases with -increased dose of application, more being in the local varieties(Table-8, col. 4i" 5" and"8", "9) than IR-8.

The dry matter yield in both varieties decreased with increased. -plant manganese and iron concentration (Table-7 and 8).

- 44 -

Table - 7

Y

Experiment No*. 6Effect of Pe application'on the D.M. yield (in gm) and leaf Fe content (in P.P.M.) of

_ _. ____ — -_ . .- •' . . . _ * _ _ i _ ___ — * -1» •• i . • j rt- a.-A- I 7 rt n Why) £if\ A ft tm r% f 4* SN4* 4» Y*A Wm V\l O V»^ •! **l n» 1

1

„ 59 -• • jFe^ appliedin P. P.M.

Control

Foliar 10

Spray 15

2550

Soil 10

Appli-cation gel

50

IRRI (IR - 8) . _„'Total dry matter

3C 601.330

0.717

3.592

3.591

0,725 3.310

0.620

! 0.350

, 0.956

0.649

4.800

3.876

4.775

5.479

0.820 I 3.548

0.636 5.502 '.

Total Fe(PPM)

30315

298

342

469

374

310

382

398

432

60206

210

169

226

198

280

195

232

265

•PPM of Fe?7

30 60-

59 i 50

65

168

126-

4

IS

30

88

108

158

84

77 J

159

146

321

Local (Naizersail)Total ^.ry j 1'otal ^©(PPM)matter

300.655

0.741

0.252

0.432

0.460

60 304.561

4.204

7.037

5.846

3,993

243

485

243

419

60

^m oi fQjy

30 j 60223 - ! -

t i

317

276

165-

311 •( - 225

0.766 5.260 ! 272i '0.866

0.629

0.549

3. 9H

5.657

1.644 '

377

367

451

151

280

226

58 ' 61 1

119 j 130 j

84 85 !

253 i 56

26 I 62 ,

20 1 80

57 | 133

308 67 j 272

Tatle - 8Experiment Ho• 6

Effect of Mn application on the D.M. yield (in gm) and leaf Mn content (in P.P.M.) oflocal and IRRI rice at various days of harvest (30 and 60 days after transplanting).

Mn54 appll«*.in P.P.k.

Control

Foliar 20

Spray 30

60

100 .

20

30Soilappli- 60cation

100

IRRI (IR - 8 ) Local (Naizersail)1 54

Total dry matter j PPM of Mn'H

30

1.330

1.065

'0,625

0,922

0.350

. 0.454

0.595•0.429

0.364

60

I 3.592

30 j 60

-

3.50 ! 86

3.635 228

2.268 j 300

4.338

2.220

1.560

1.672

2.063

608

37

58

170

218!

-

84

175

380

.644

101

243

440

840

Total dry matter50

0.655

0.480

1.15

0.435

0.3550.402

0.365

0.405

0.588

60

4.561

6.315

4.754

3.850

5.753

2. -696

2.524

2.770

• 1.105

PPM of Mn54

•30

-

146

155390

523

- 58

89

281

216

60

-

109

109

421

519

75

236

219

692

Summary*The ultimate goal of all agricultural experiments is to achieve

increased production and with this point in view an attempt has beenmade to summarise some of the experiments with valuable information.This is only an attempt to throw some light on the performance andnutrient requirement of low and high yielding rice, but definitely nota chapter closed for discussion.

Experiments conducted in various seasons with different varietiesof Tice using major and minor elements, i.e. N, P, K, Ca, Pe, Mfc . eto.are summarised here.

The following conclusion may be drawm -

1. Nutrient contents of rice plants vary depending on the crop season,even in the same variety. Boro (Summer) appears to be the richest in respectof N P K and Aus (Autumn) in respect of Ca-content.

2. The phorphorus uptake was the highest from the surface applicationof superphosphate under water-logged condition and also from mixing ofsurface and subsurface soils in pot experiments.

323« P uptake increases when the source of nitrogen is urea as-ffomparedto ammonium sulphate. '.

4* Field trial showed urea to be a better source of nitrogen thanammonium sulphate in lateritic-soils in respect of grain production. Lowyielding local Aman rice (var - Naizersail) does not respond beyond 60 IbsN/acre while in the same season IR-8 showed progressively increased yieldupto 180 Ibs N/aore. Potassium seems to be non-responsive in clay soils.

- 47 -

5. N P K content of 65 day old leaves were more in IRRI varietiesthan in local varieties in Aman season as well as in P ro season.

6* Overall nutrient content of the same IRRI variety in Boro seasonis much more higher than that in Aman season resulting in higher grainproduction,

7. Leaf N-contents in Boro were found to be 3«5 &nd that in Amanis 2.5 percent' indicating that increased N-content is related to higheryield.

8. Higher rate of N-application decreases the Ca-content of 65 dayseld leaf in both varieties, decline being sharp in IRRI. Liming improvesthe crop yield effecting both soil reaction and Ca-nutrltion.

9. Chlorophyll content of leaf increased with higher N-applioationupto 90 Ibs N/acre in local and 120 Ibs N/acre in IRRI varieties, beingmore chlorophyll content in IRRI.

10. Third leaf analysis at pre -primordial stage seems to be a promisingtool for adequate fertilization of rice crops like many other short durationcrops .

AcknowledgementThe authors wish to record their gratitude to the members of the Plant

Physiology Section for the technical assistance rendered in connection withthis work. They also express their sincere gratitude to other members of thisCentre for their co-operation.

- 48-

References

1. Agri. Asia 1966 (English Edition). Association of AgriculturalRelations in Asia, pp 275-276.

2. Islam, M. A., (1965), Fertilizer problem of Eaat Pakistan,pp - 1, unpublished.

3. Karim, M., Rahman, M., Sandhu, M.S., Patwary, S. and Bashir, M.(1969). Liming of acidic rice soils (unpublished),

4. Rice production manual, University of the Philippines (1967)pp 43 - 60.

5. Tanaka, A., Novasero, S.A. (1966) Soil Soi. P3. Nutr. 12_ (5).197 - 201.

- 49 -

INTERNATIONAL ATOMIC ENERGY AGENCYin cooperation with

theFOOD AND AGRICULTURE ORGANIZATION OF THE UNITED NATIONSCountries of Asia and the Far East Study Group Meeting

on theUse of Isotopes and Radiation in Investigations of Fertilizer

and Water Use Efficiency

Bangkok, Thailand21-25 April 1969

A Study on the Efficiency of Shallow and Surface Placement ofNitrogen and Phosphorus Fertilizers Applied Separately andChemically Combined Form by Using Isotope Technique--'

. - ' •Sombhot Suwanwaong, Patoom Sanitwongse and Prayoon Sawatdee

Technical Division, Rice Department, Ministry of Agriculture,Bangkok, Thailand

OBJECTIVES1. To compare the efficiency of different chemically combinednitrogen/phosphorus sources with ammonium sulphate plus super-phosphate .

I/ Report of experiments conducted in Thailand under a researchcontract in the IAEA coordinated program on the applicationof isotopes and radiation in rice cultivation (1967-1968).

- 50 -

2. To compare the efficiency of ammonium sulphate plus superphosphateand different chemically combined nitrogen/phosphorous sources asinfluenced by shallow placement at transplanting and surface placementtwo weeks before initiation of panicle primordia.

MATERIALS AND METHODS

1. Experimental site; The experiment was conducted at Rangsit RiceExperiment Station, Pathum Tani Province located about JO kilometersnorth of Bangkok.

2. Soil at experimental site;The soil at experimental site is a moderatelyacid sulphate soil formerly part of the tidal flats with heavy clay texturedeveloped from brackish water alluvium belonging to the Rangsit series (Rs),The chemical properties of this soil at the experimental site are given intable 1. Kaolin minerals are prevalent throughout the profile whilevermiculite, illite and montmorillonite are sub-species. The details of theclay mineral composition reported by K. Kawaguchi, Kyoto University, Japanare as follows?

Composition of clay Composition of nextminerals left, columnnui •j.&uu

135

Kaolin

454540

Illite

201520

intergrade, Mont. Verm. Al-Verm. t 11

mixed layer

35 + ++ + +40 + ++ + +40 -i- ++ + . ±

Note: 1. The figures in columns 2, 3 and 4 are from the approximate amountof crystalline minerals in percent, deduced from the measurement of theheight and area of X-ray diffraction peaks.2. "Mont-Verm intergrade, mixed layers" include montmorillonite,vermiculite, their intergrade and mixed layer minerals.

3. Bice variety The rice variety employed in the experiments wasNahng Mon S-4 which can be characterized as a tall, medium-late,non-glutinous, photo period sensitive variety, normally maturingabout 20 November. It is typical of the Indica type used in thelowland transplanted areas of the Central Plain.

4. Experimental Method: The design ;f the experiment was the same as thatsuggested by IAEA and consisted of a Randomized Complete Block with 4replications. Each replication contained a total of 10 main plots ortreatments herein designated A through J. Eight of the treatments(A through H) were concerned with (l) sources of N and P, (2) placementof the fertilizer and (3) time of application. Plots A through D hadfertilizer applied at planting time in rows at a 5 centimeter depth whiletreatments E through H had fertilizer applied broadcast on the soilsurface two weeks before panicle initiation. The treatments A and Ereceived superphosphate broadcast at transplanting and two weeks priorto panicle initiation, respectively, since there was no phosphorouschemically combined with the nitrogen. All 8 treatments received 60 Kg.of N per hectare using the different sources of nitrogen applied aspreviously stated with spacing of 25 x 25 centimeters.

Treatment I was a maximum yield response plot using 120 Kg. Nper hectare in the form of ammonium sulphate applied in rows at a 5centimeter depth at transplanting time. The treatment was subdividedinto two equal plots referred to here as I, and I2 in which plant spacingwas 25 x 25 and 25 x 34 centimeters respectively.

-Treatment J was also subdivided equally into 2 plots called J,and J2 to compare the effect of P and K in the absence of N. This alsoserved as a control for the experiment. J? received no fertilizerwhereas J., received 60 Kg. each of P Oc an<* KO° per hectare.

- 52 -

All plots except J2 received 60 Kg, KgO per hectare "broadcastimmediately after applicatlon-of •the" nitrogen and phosphorous treat-ment justjbefore transplanting. .•. .......

•' 'Both radioactive and non-radioactive superphosphate, as well asthe N-15 labelled and non-labelled nitrogen fertilizer were appliedat the same rate and same -time according to the fertilizer treatments.The following outline gives a description of each treatment in detail.

Treatment.

E

E

Placement and TimingN - Fertilizer

ammonium sulphate applied attransplanting in rows at 5 cm.depth.ammophos 3 applied at trans-planting in rows at 5 °n».depth.

nitric phosphate (75 fo solubleP) applied at transplantingin rows at 5 cni« depth.

nitric phosphate (25 %soluble P) applied attransplanting in rowsat 5 cro depth.

Ammonium sulphate applied2 weeks before primordialinitiation, broadcast onthe surface.

P - Fertilizersuperphosphate applied attransplanting broadcast onthe surface.phosphate applied combinedwith y.

phosphate applied combinedwith N.

phosphate applied combinedwith H.

superphosphate applied2 weeks before panicleinitiation, broadcast onthe surface.

' - 53 -

Treatment

P

H

Placement and TimingN - Fertilizer P - Fertilizer

Ammo-Phos B applied twoweeks before primordialinitiation, "beforeprimordial initiation,broadcast on the surface

nitric phosphate (75 %soluble P) applied2 weeks before primor-dial initiation, broad-oast on the surface*

nitric phosphate (25 %soluble P) applied 2weeks before primordialinitiation, broadcaston the surface.

This is the yield responseplot and N in the form ofammonium sulphate is appliedat transplanting in rows at5 cm. depth and at the rateof 120 Kg. N per hectare.Superphosphate at the rate of60 Kg. P2°c Per hectare isapplied at transplanting,broadcast on the surface.This plot was divided intotwo equal sub-plots I, and

phosphate applied combinedwith N.

phosphate applied combinedwith N.

phosphate applied combinedwith H.

- 54 -

Treatment Placement and Timing

N-Fertilizer P - FertilizerJ This is the zero fertilizer

control plot (yield check)and was divided equally intotwo sub-plots J, .a.nd Jg.

Note: Rice was transplanted July 15, 1967 and harvested November 26, 196?.

SUMMARY;A study on the efficiency of shallow and surface placement of nitrogen

and phosphorous fertilizer applied separately and in chemically combinedform by using isotope techniques was conducted in 1967-1968 at the RingsitRice Experiment Station, Pathum Tani province. The soil at experimentalsite is a moderately acid sulphate soil with heavy clay texture. The prevalent

Hclay mineral is kaolin with low p and base saturation but high in organicmatter. This soil belongs to the Rangsit series (R_). The results of the5experiment may be summarized as follows:

1. According to the.results of the experiment on the yield and yieldcomponents, it was found that both ammonium sulphate plus superphosphateand chemically combined nitrogen/phosphorous fertilizers, when applied attransplanting or two weeks before initiation of panicle primordia gavesignificantly higher number of tillers, height, number of panicles, grainand straw than those of check plots (Table 2, 3 and 5).

2. Considering application of fertilizer at transplanting the yield componentswere not significantly different regardless of fertilizer sources. However,grain yield obtained from ammonium sulphate plus superphosphate and fromammo-phos was significantly higher than those from both nitric phosphatesources.

- 55 -

3. When the four kinds of fertilizers were applied at two weeks beforeinitiation of panicle primordia, it was found that there was no significantdifference among yield components and grain yield but there was atendency toward lower yield in treatments using nitric phosphate fertilizer.

4. When the two methods of fertilizer application were compared, it showedthat in general the fertilizer application at transplanting time gave morenumber of tillers, number of panicles, grain yield, straw yield, straw-grainratio and total dry matter production than the later fertilizer application.On the other hand, the later application gave higher panicle weight andnumber of grains per panicle.

5. Analyses on the recovery of nitrogen and phosphorous derived fromfertilizer were performed on the 8 treatments (A through H) using leafsamples at 3 different stages of growth and in the grain and straw atharvest time (table 4). Prom the data obtained it was revealed that whenthe fertilizer was applied at transplanting (A through D) in rows ata 5 centimeter depth the plant recovery of nitrogen derived from nitricphosphate, 25 percent soluble P, was lower than those of the other fertilizertreatments at all stages of leaf growth as well as in grain and straw,while the other three fertilizers showed no difference in this respect.On the other hand, when these sources of fertilizer were applied broadcaston the surface at two weeks before initiation of panicle primordial(E through H) it was observed that there was not much difference in percentof nitrogen derived from the different fertilizer sources. However it canbe noted that nitrogen derived fromammo-phos was consistently higher at allstages even though statistical analysis did not indicate significantdifferences.' When both stages of fertilizer applications were compared, thepercentage of nitrogen derived from fertilizer applied at transplantingwas slightly higher than the later application. It is interesting to notethat regardless of fertilizer sources, there was a very high positive asso-ciation between uptake of nitrogen and phosphorous at both first and secondharvesting of the leaves.

6. From the yield obtained (.Table 5) and the percentage' of nitrogenand phosphorous derived from fertilizer (Table 4) it was clear thatnitric phosphate, 25 percent soluble P, was inferior to: both the'ammonium sulphate plus superphosphate and amroophos, although therewas practically rio difference in efficiency between these two latterfertilizers. In Comparing nitric phosphate sources, the 75 percent solubleP is better than 'nitric phsophate 25 percent soluble P although lit islower than the other two sources. . . . . :

ACKNOWLEDGEMENTThe authors wish to express* their sincere gratitude |to Dr. Ben R.Jackson,

Dr. J. Takahashi and Dr. Sarot Montrakul for their corrections and helpfuladvise in preparing this paper.

Special acknowledgement is due to IAEA for the material and academicsupports. Warm appreciation is extended to fellow workers of the RiceDepartment especially to the staff of the Rangsit Experiment Station for

! 1their helpful cooperation, in this experiment.

- 57 -

Table 1. Analysis of soil at the experimental site*

cm! *' ***'

III

0-20 IIl

IV

Averagesi? I

II20-40 ra

IV

iH20

4.24-54.24.2

4.2

4.04.04.04.0

pH1 HKC15.45.45.45.45.43.23.23.20.8

sA0.80.90.80.8

0.8

0.80.80.80.8

O.M.:

3-593.485.225.175.571.722.081.721.61

Available!Pppm.7.99.27.17.6

7.92.65.02.51.7

Kppm. _65.659.661.665.6

65.146.053.657.661.6

*°lal, mei/lOOg.H*

0.160.160.160.15

0.16

0.100.110.100.09

28.3828.6928.7028.58

28.5925.7226.9527.2027.05

Exch: Baseme./100{

13.7414.1814.4414.4414.20

9.7510.6512.4912.58

Exoh.5. K+

0.630.600.660.60

0.62

0.410.580.450.58

Cation me./lOOg.

7.176.586.617.476.965.185-455-735-75

***8.028.869.208.91

8.758.068.528.878.62

•.**2.002.041.992.00

2.01

2.172.242.162.55

BaseSat

48.0949.7749.5550.10

49.3838.0039.4246.6446.11

TextureSand

11.310.511.59.210.6

11.511.211.411.2

Sitl

16.118.215.416.3

16.516.116.116.112.2

Clay

72i671.373.174.572.972.472.772.576.6

Averagft 4.0 3.2 0.8 1.78 2.4 54.7 0.10 26.73 11.37 0.41 5-53 8.47 2.28 42.54 11.3 15.1 73.6

Table 2. Tillering of Bioe Plants at Various Stage

Treatment Average Number of Tiller per hill

ABCDEPGHIIJlJ2

30 days /11.9610.8410.7210.453.343.303 .'093.08

10.15. 11.21

3.563.29

57 days /12.5111.6011.6311.123.363.413.303.30

13.8018.053-57

-3.74

71 days /9.849.259.118.95

10.6610.37•9.529.43

10.9514.073.643.79

131 days /9.199.028.327.936.475-835.655.919.82

12.133.453.47

HSD - O.t>5~ -1.&4 1-.32 - - 1-.-48-- 1.25

l/ Mean of four replications.2/ Tillering of rice plants at the time of half way between transplanting

and two weeks before primordial initiation (14 August 1967)..,Tillering of rice plants at the time of two weeks before primordialinitiation (11 Sept. 1967). . .Tillering of rice plants at the time of the intermediate harvest atprimordial initiation (25 September. 1967)..Tillering of rice plants at the time of. harvesting (26 November 1967).

- 59 -

Table 5. Height of Rice Plants at Various Stages /

Treatment Average Height of Rice Plants (cms)

ABCD£PaHIxI2JlJ2

HSD

nu

2J30 days=

74.5475.7677.0270.9051.9452.9353.3452.0674.6474.4055.4353.57"

- 0.05 '4.67

57 days /

114.36111.74107.1096.1269.5769.7969.2370.10131.06136.0070.6669.60

• 7.88

71 days /

132.85126.98121.53107.89114.03112.26106.90109.65154.58159.8281.4180.15"

8.91

131 days /

176.47166.58159.68151.48171.81165.54160.22160.66201 .09208.17133.69

" "132.21

6.79

Mean of four replications.Height of rice plants at the time half way between transplantingand two weeks before primordial initiation (14 August 1967)Height of rice plants at the time of two weeks before primordialinitiation (ll September 1967)Height of rice plants at the time of the intermediate harvest atprimordial initiation (25 September 1967)Height of rice plants at the time of harvesting (26 November 1967)

- 60 -

Table 4. Height of leaf cample grain and straw and percentage of total nitrogen,phosphorus and the percent derived from fertilizer at various stages ofgrowth in Isotope-plots.

Tr.

ABCDEFGH

&

HSD -0.05

First Harvesting*/Dry wt.

e7.807.036.796.053.723.703.583.50-

0.71

NitrogenTotal

1.901.761.671.58----

1.91

0.15

DFF

74.278.677.959.9-----

5.0

PhosphorusTotal

.141

.115

.119

.135-----

.02

DFF

61.961.961.253.8-----

6.7

Second Harvest ing£/Dry wt^

S

7.677.236.325.755.105.634.304.24-

1.27

Nitrogen PhosphorusTotal

1.541.401.281.342.713.032.302.14-

0.65

DFF

72.176.676.158.161.779-556.648.0

—

14.0

Total

.099

.094

.091

.115

.246

.217

.216

.174—

.04

DFF

70.0

51.354.547.950.358.256.050.8-

16.8

Third Harvesting^'/ .Dry wl/

g

7.907.126.565.726.966.986.626.71

—

1.28

NitrogsnTotal

1.061.010.941.021.611.551.561.44

—

0.17

IFF

63.2

66.466.148.849.264.459.248.9

—

10.0

Fourth Harvesting-^Grf3jj,p

Nitrogen"Total

0.890.870.82

0.850.880.850.860.87

—

NS

br r

52.552.849.633.539.847.742.733.0

—

10.0

RtIfi

TotaJ

0.29

0.270.28

0.310.300.300.290.31

—

0.03

-T .=» W _tropen

41.049.047.033.341.547.946.835.9

—

ND

I/ At 2 weeks before primordial initiation (12 Septe. 1967).2/ At primordial initiation (26 Sept. 1967).IJ At flowering (26 Oct. 1967).4/ At harvesting (26 Kov. 1967).5_/ Mean of four replications of twenty sev n leaves.6/ Composite sample of treatment E F G H.

Table '§. Yield components of rice plants at harvest.

j No. of :Treatment Panicle/

: Hill :

A 9.19B 9.02C 8.32D 7.93E 6.47P 5.83G 5-65H 5.91Ix 9.82I2 12.13Jx 3. 5J l tt^9j *^ m

USD - 0.05 1.25

Paniclewt.gra.

3.182.852.892.864.024.514.424.633.583.853.463.18

0.90

: No. ofgrain/

: panicle

84.4779.1580.3679.20107.79120.77122.58124.5798.83107.5898.7592.13

24.70

: wt./lOOO :grain

: gnu :

33.1332.9333.1632.9934.2734.1233.9934.0633.3232.7431.6231.57

0.90

Grain Yield :Kg./Ha.

3,904.183,533.113,088.902,762.413,264.993,067.712,855.782,909.054,955.664,799.871,551.711,518.66

493il8

Straw YieldKg./Ha.

10,222.359, 416.417,313.435,911.934,663.024,372.653,896.354,048,6513,077.9413,002.381,864.771,77 .84

1,909;09

: Ratio :straw/grain

2.622.662.372.141.431.421.361.392.642.711.201.17

0.36

Total dry matt'production

Kg./Ha.

14,271.3213,069,9910,505.508,773.998,039.747,551.256,805.397,055.0918,218.1517,996.903,475.883,347.06

2,238.55

Mean of four replication from yield plots.

RECENT SOIL, FERTIBIZER AND PHYSIOLOGICAL STUDIESWITH 32p ON HIGH YIELDING VARIETIES OP

PADDY

B.V. Subbiah and J.C. KatyalNuclear Research Laboratory, Indian Agricultural

Research Institute, Delhi, India

ABSTRACTA knowledge of the rooting pattern of high yielding paddy varieties is of

considerable importance in soil,water and fertilizer management problems. Studieswere carried out on the applicability of the 2p plant injection technique forpaddy, comparison of the results of root activity obtained by,the placement ofP in different soil zones and root distribution pattern by P plant injection

technique, the root distribution pattern of some of the high yielding dwarf paddyvarieties as compared to local ones, and effect of nitrogen fertilization on therooting pattern of a dwarf variety. The results in brief are as followss-

(a) T* plant injection technique was found to be applicable for paddy forevaluation of root distribution and injecting ^p into the plant with sucrose wasfound to result in increased transport of the activity from the stem to the roots.

(b) The root activity data by P placement (in capsules) gave statisticallyreproducible results which are highly correlated with the root distributionpattern obtained by i2p plant injection technique.

(c) The high yielding dwarf varieties (viz. IH-8 and Taichung Native l) werefound to have more intensity of root distribution in lower depths as compared tolocal tall variety (Viz NP 130).

(d) Effect of increasing levels of nitrogen fertilization was found to resultin a greater intensity of root distribution in lower depths.

- 61 -

RECENT SOIL, FERTILIZER AND PHYSIOLOGICAL STUDIT3S WITHOF- HIGH YIELDING .VARIETIES OF PADDY

B.V. Subbiah and J.C. KatyalNuclear Research Laboratory

Indian Agricultural Research InstituteDelhi India

1. INTRODUCTION!*fith the recent introduction of high-yielding varieties which are being

further crossed with local varieties to bring about certain desirable characters,new problems in soil fertility and water management are coming up for sblution.Since the roots are principal organs of a plant through which nutrients and waterare absorbed, .the knowledge of the characteristic rooting habits and relativeactivity of -|;he roots in different soil zones of these high yielding varietiesis essential for bringing about efficient ssoil, water and fertilizer management.Very little is known about the exact rooting pattern of these recently introducedpaddy'varieties, because of difficulties involved in such-studies. In the presentpaper (a) the applicability and standardization -of •* P plant injection technique(6, ?) for paddy, (b) comparison of results obtained by this technique with thoseof 32p Uptake, by activity placement (in capsules) in different soil zones, (c)evaluation of the rooting pattern of some high yielding paddy varieties, and (d)effect of different levels of nitrogen fertilization on root distribution of adwarf paddy variety have been studied and results discussed.

2. MATERIALS AND METHODS2.1 Standardization of T* plant injection technique:

Plants of paddy variety Taichung Native I (dwarf) were grown in solutionculture using standard Hoagland's nutrient solution, using 0.5$ Ferric ammoniumcitrate. One ml of this iron solution was also added daily to each porcelain potof one litre capacity. One plant was grown in each pot. Nutrient solution waschanged once or twice a week. Nutrient solution in the pots was aerated for 5-6hours each day using a compresser and glass tubing with multiple openings. Dueto synchronized tillering habit of the variety used, a suite.ftle tiller at ,pflowering stage was selected for injection. Ten microcuries of carrier-free Pin 0.0? ml. in the form of E 2PO. (in HCl) was injected in the second internodeusing a micro syringe (6, 7). In order to study if there is a beneficial effectof injecting carrier-free ^P with sucrose on the movement and distribution of*2p in the plant, two treatments namely with and without 0.1 M sucrose wereincluded. A second micro syringe was used to create suction in the same internodeatra point about 3-4 cm. above the first syringe. Root and shoot samples wereseparated by cutting the plant at the base of the stem at time intervals of 1,3and 6 days after injection. Roots were washed thoroughly to remove nutrientsolution sticking to them. Roots were divided depending upon the length, into3 or 4 parts of about 5 cm. length and each used separately for specific activitydetermination. Injected tiller in each case was separated. Uninjected tillerswere separated and each used individually for specific activity determination.However, for samples of 1st and 3rd day 2 tillers were combined in order to reducethe number of samples.

- 62 -

2.2 Estimation of specific activity of plant samples:Both root and shoot samples for each day were dried in an oven and oven dry

weight recorded. Dried samples were ground in a Wiley micro mill, total phospho-rus determined by "Vanado molybdo phosphatic yellow colour method" (l). One mg -P equivalent solution was taken and P precipitated as magnesium ammonium phosphate(5) with the modification using 50$ triammonium citrate which has been found tobe. equally suitable in place of 50$ ammonium citrate. The precipitate wasfiltered under identicall conditions using demountable' falteration set. The driedand mounted precipitate was counted using a G.K. end window decade sealer counter.Specific activity data were calculated after making necessary corrections.2.3 Field Studies

32 °2.3.1 Assessment of root activity pattern by P placement.32 / / \In this experiment carrier-free P was mixed with KgSO. (50 uc/12 mg. KgSO.).

K/jSO. was dissolved in minimum amount of water in a mortar and carrier-free32p tdded to correspond to 50 uc per 12 mg. of K SO.. This active, solution wasthoroughly stirred and dried under infra-rod lamp with intermittent mixing of thematerial. After drying it was ground thoroughly in a glove box. Twelve mg. ofthis material was weighed accurately (using a percision balance) each time andput in the gelatinous capsules. Capsules were closed carefully with their caps.

One month old nursery of variety Taichung Native I (dwarf) was transplantedin the plots of dimensions 6m x 6m. 12.5 cm from plant to plant and 20 cm. fromrow to row distance was given. Two healthy seedlings were transplanted each hill.A basal dose of 100 kg. of N (half at the time of transplanting and half afterone month of transplanting) as urea and $0 kg. P00K as super phosphate per hectarewere added before puddling and urea fcfter

After 15 days of transplanting four capsules were put around each plant atequal distances on the periphery of a circle. The different lateral distancesfrom the plants were 2.5 cm (L,). 12.5 (Lp) and 22.5 cm. (L,) and depths were4 cm (d,), 12 cm (d?), 20 cm (a,) and 28 cm (d,). The holes were made at theselateral distances and depths by a thick and sharp iron rod and after placing thecapsules the holes were closed completely by filling with soil. Plants wherecapsules were placed were labelled.

At the flowering stage above ground parts of the capsule placed plants wereharvested and used for specific activity determination (as described above).Specific activity data for three replicates after necessary corrections were usedfor calculating the percentage root activity in each zone.

322.3.2 Root distribution pattern by P plant injection technique:2.3.2.1 1967 Studies: During this year two varieties of paddy viz IR-8 (dwarf)and Taichung Native I (dwarf) were grown in the fields (15 Main Block, AgronomyFarm, I.A.R.I.Delhi) using the same distances as mentioned earlier. Ten rows ofeach variety were transplanted in a plot of about 2.5 m x 6 m. Two plants wereput per hill. Fertilizer dosage and method of application were same as above. Atflowering stage when the soil! was at about field capacity one suitable tiller ofa healthy plant was injected with carrier-free 2P using 5*0 uc in 0.125 ml.Three plants of each variety were injected. After giving six days for ^2p ^o"equilibrate in whole of the plant body, above ground parts of the plant were cutoff and soil samples were taken at lateral distances of 2.5 cm (L,) 12.5 cm (L?)and 22.5 cm (Lj) and depths of 0-8 cm (dj), 9-16 cm (dg), 17-24 cm (d,), 25-32 cm(d.) using a tube auger. Four samples were taken at each lateral distance

- 63 -

and depth around the plant and mixed. The samples were taken when the surfacesoil was below field capacity. Each composite sample was labelled (showing thelateral distance and depth) and kept in polythene bag. These soil samples withroots were air dried and ground. About 50 S® of each sample was ignited in amuffle furnace at 500° C for two hours. The ashed samples were ground thoroughlyto ensure the uniform mixing of the activity with soil and filled in cuppedplanchets (0.625 cra depth). The surf an-, was levelled by using a steel spatula.The weight of the soil in each planchet was recorded. (This weight was found tobe almost constant.) The counts for 5^0 seconds were taken using end windowG.M. Counter. After making the necessary corrections the percentage root distri-bution by counts was calculated.g.3.2.2 1968 Studies: During this year four paddy varieties viz NP 130 (tall,local variety) Taichung Native I (dwarf), BC 5 and 5C 6 (both obtained by crossingTaichung Native I X local tall variety basmati 370 and both these are dwarfs)transplanted after one month of sowing in 15 Main Block of Agronomy Farm. Methodof transplanting, date of transplanting, spacing used, fertilizers applied were.exactly the same as in the previous year's experiment. At flowering stage threeplants were injected and collection of coil samples at various depths and lateraldistance, ignition, counting etc. were exactly the samo as above.2.3.2.3 During this year another experiment was set up to study the effect ofdifferent levels of N fertilization on root distribution of variety TaichungNative I. Levels of N used were 0, 70, 140 and 210 kg N/ha. This experiment waslaid out according tc randomized block design using three replications. Rest ofthe conditions were exactly the same as above, and root distribution was made atthe flowering stage as in other experiments.

Some of the important soil characters are summarized in table I a and varietalcharacteristics in table Ib.

The soils of the fields where experiments were carried out as can be seen fromtable I are silty clay loams with pH ranging from 8.0 - 8.5 and bulk density 1.18 -1.32 in all the depths where root distribution studies are made. The soils arefairly rich in total nitrogen and available phosphorus and are known to have goodamounts of potassium.

3. RTOULTS323.1 Standardization of P plant injection technique:

32The results obtained on the P distribution in different parts of paddy plantafter 1, 3 and 6 days of injection are presented in table II.

The data in table II show that more than 88$ of the activity has remained inthe injected tiller even after six days of injection, although there was a trendof slow decrease in the activity in the injected tiller with time. However, inthe uninjected.tillers the amount of activity moved, increased with time. But onevery striking feature of the data is that a fairly good amount of activity movedin the roots on the first day. In case of suoros.- treatme.it there was about 2.9$of the total injected activity in the routs on the first day, 1.9$ on the thirdday and 3.4$ on the sixth day, while in case of no sucrose treatment the corre-sponding figures were 2.7$, 1.2$ and 1.4$ respectively. In general the sucrosetreatment resulted in a greater amount of activity aft^r 3rd and 6th day in roots.

From the point ' of view of applicability of the technique for the estimationof the root distribution, it is essential to have uniform specific activity inthe entire root system. From this point of view the data obtained on the specific

- 64 -

activity in the different parts of the roots is presented in table III. It showsthat there are big variations in the specific activity of different root parts onthe first and third day but tend to become more uniform after the sixth day.Thus this method for the estimation of the root system will be applicable in thelight of these findings. Hence this period of six days was choosen for collectionof soil root cores in the subsequent field studies.

323.C Studies on root activity by P placement:32One of the main difficulties in soil P injection technique for assessment

of root activity in the field (3) is the high coefficient of variation betweenthe replicates (2). Subsequent development of placing tagged super phosphate indifferent soil zones has also not overcome these difficulties. Thus in thepresent work an attempt has been made to bring about uniformity in application ofactivity in different soil locations by preparing a solid adsorbed phase ofKpSO. (as per details given in materials and methods) at the time of applicationbut carrying out the tagging in the liquid phase. Each capsule contained 12 mgof K2SO. carrying 50 uc of 2P. Four capsules were placed around the plant atthe lateral distances and depths mentioned above. Placement of such capsules ateach location will ensure uniform distribution of applied carrier free *2pwithout disturbing the P content of the zone.

The specific activity data obtained for different depths and lateraldistances averaged for three replicates is given in table IV. These results showthat for variety Taichung Native I the root activity at d,L, representing the 2Puptake from a depth of 4 cm and lateral distance of 2.5 cm as highest and formsmore than one third of the total uptake. The total intensity of root activityin all the horizontal distances at depth d, (4 cm) is 57 • 5 Per cent. On theother hand if d,, d_ depths are combined for first two lateral distances i.e.up to 12.5 cm it is about 79$. Hence it can be said that the intensity of feedingis higher at a depth of 12 cm and up to lateral distance of 12.5 cm.

323.3 Varietal differences in root distribution pattern by P plant injectionmethod:The percentage root distribution of varieties TN-1, (1967-68) NP 130 (196?),

IR-8 (1967), BC 5 (1968) and BC 6 (1968) are given in table V. In case ofvariety Taichung Native I the bulk of the root distribution is up to d2L, (i.e.up to a depth of 16 cm and lateral distance of 2.5 cm) and d-jLp (i.e. up to adepth of 8 cm and lateral distance of 2.5 cm). The same pattern is obtained inthe second year on a more or less similar soil.

However, in case of variety NP 130, a local basmati tall variety, bulk ofthe root distribution is confined to d,Lp (i.e. up to a depth of 8 cm and lateraldistance of 12.5 cro). Showing thereby, it has got a more shallow root system ascompared to variety Taichung Native I.

In case of variety IR-8 the pattern is somewhat similar to that of TaichungNative I.

In case of BC5 and TJC6 which are basmati dwarfs, the root distributionpattern is confined to surface like NP130.

- 65 -

323.4 Comparison of results obtained by capsule method and P plant injectionmethod:

32It will be of interest to compare the results obtained by P plant injectiontechnique with those of capsule method. The two sets of results gave more or lesssimilar pattern, except that from the point of view of root activity the d?depth has not shown values as high as the values revealed by the data of rootdistribution pattern. But in general there was a significant correlation (r=0.98)between these two sets of values, showing thereby that *2p plant injection ••»technique which gives root distribution pattern also correlated well with theuptake of phosphorus.3.5 Effect of different levels of N:

As Nitrogen is one of the main yield increasing components, study was made toassess the effect of different levels of N (0,70,140)and 210 Kg. N/ha) on therooting pattern of Taichung Native I. As is evident from the data in taftle VIthe effect of increasing level of N has been to bring about a greater feeding ind« zone at the expense of d, zone. This in this variety increased level of Nfertilization has resulted in greater subsoil feeding which will be an importantfactor in the areas where assured water supply does not exist.

4. DISCUSSION32From the point of view of applicability of P plant injection technique for

paddy the results clearly indicate that the uniform specific activity is obtainedafter six days of injection. It is of particular interest to note that bulk of theinjected 32p still remained in the injected tiller. For increasing the accuracyof the technique it is desirable to bring about a greater transport of the injected32P into the roots. Earlier attempts (4) using indole acetic acid has n'ot metwith any good' succ'ess in bringing about the greater proportion of the injected32p in the root system.. In the present investigation, use of 0.1 M ducrososolution kas made to see the effect in the movement of -^P in the roots ascompared to one without sucrose. While more work is necessary to find out theother means of increasing this transport, at present sucrose appears to bo themost promising carrier for bringing about greater activity into roots, thusincreasing the accuracy of the subsequent estimation of root distribution patternunder field conditions.

32While P plant injection technique appears to be most promising method forassessment of root distribution of cereals, the method at best gives the amount ofroots present in the different soil zones and not the root activity.,_It isdesirable, to assess how far the rpojb distribution data obtained by P plantinjection technique gives a picture of the nutrient uptake from different soilones. In this respect the comparative data obtained by the two methods, namely

placement (in capsules) in different soil zones agreed remarkably, thecorrelation coefficient being 0.98 which is highly significant. Thus, similarinformation could be obtained by either of the methods. The'only consideration forthe choice being, the ease of technique and the labour involved. From this pointof view 32p plant injection technique offers a unique and elegant means ofobtaining the rooting pattern in soils under natural field conditions for cerealcrops.

Using P plant injection technique the root distribution pattern of some ofthe high yielding varieties, currently being cultivated in India, has been esti-mated. These results clearly show that although, paddy in general, is a shallow

- 66 -

rooted crop, the dwarf varieties are comparatively more deep rooted as comparedto local tall varieties. This character confers a distinct advantage from thepoint of view of drought resistance and lodging. Although the rooting patternof the new crosses "HC5 and BC6 is like that of NP130, but BC5 is comparativelydeep rooted than the BC6 variety.

It is of interest to note'the effect of higher levels of nitrogen fertili-zation on the rooting pattern of the high yielding dwarf variety, TaichungNative I. The increased fertilization gave deeper rooting pattern. Thisfinding may be of significance during the seasons of uncertain water supply.For example, recently when there was drought in the paddy areas-Taichung Native Isurvived much better than local varieties.

5. SUMMARY

A knowledge of the rooting-pattern of high yielding paddy varieties is ofconsiderable importance in soil water and fertilizer management problems.Studies were carried out on the applicability of the "p.plant injection techni-que for paddy, comparison of the results of root activity obtained by the ,_placement of *2p in different soil zones and root distribution pattern by Pplant'injection technique, the root distribution pattern of the some of thehigh yielding dwarf paddy varieties as compared to local ones, and effect ofnitrogen fertilization on the rooting pattern of a dwarf variety. The resultsin brief are as follows:-

(a) P plant injection technique was found to be applicable for paddy forevaluation of root distribution and injecting ^2p into tho plant with sucrosewas found to result in increased transport of the activity from the stem to theroots.

(b) The root activity data by P placement (in capsules) gave statisticallyreproducible results which are highly correlated with the root distributionpattern obtained by ^2p plant injection technique.

(c) The high yielding dwarf varieties (viz. IR-8 and Taichung Native l)were found to have more intensity of root distribution in lower depths ascompared to local tall variety (viz NP 130).

(d) The effect of increasing levels of nitrogen fertilization was found toresult in a greater intensity of root distribution in lower depths.

6. ACKNOWLEDGMENT

Grateful thanks are due to the Indian Council of Agricultural Research for agrant of a Fellowship for one of the authors (j.C. Katyal) during the period ofstudy. The authors also wish to thank Dr. N.P. Datta, Head of the Division ofSoil Science and Agricultural Chemistry, Indian Agricultural Research Institute,Delhi, for the facilities kindly made available. The authors also are deeplyindebted to Dr. M.S. Swaminathan, Director, Indian Agricultural Research Institute,Delhi, for the keen interest in this work.

- 6? -

REFERENCES

(1) BABTON, C.F., Ind.andlng.Chem.Anal. 20 (1948) 1068-73

(2) BURTON, G.W., Role of tracers in root development investigations. AtomicEnergy and Agriculture Hi. Comer, C.L. Publi.49, Amer.Assoc. for Advance-ment of Sci. Washington B.C. (1957)

(3) HALL, N.S., CHANDLT5R. W.F., VAN BAVEL, C.H.M., REID, P.H. and ANDERSON, J.H.,Tech.Bull., (1953) N. Carol.Agric. Sxp.Sta. 101

(4) HALSTEAD, E.H. and RSNNIE, D.A., Can^..J.Bot. 43_ (1965) 1359-67

(5) MACKENZIE, A.J. and D*1AN, L.A., 20 (1948) Anal.Chem. 559-60

(6) RACZ, 'G.J. , RWIE, D.A. and HUTCHEON, W.L., Cand.J.Soil 801.44 (1964) 100-832(7) REHNIE, D.A. and HALSTTSD, E.H., "A P injection method for quantitative

estimation of the-! distribution and extent of cereal grain roots" Proc.Symp. IAEA/FAO Ankara (June/July 1965) IAEA Vienna (1965) 489-504

- 68 -

Table I*

£h«aioa1 sa<! physical characteristics nf th«* st-its (P<

Soil Characteristics 15 No. 14

1$1

Textural Class

Bulk density

PK

31*cttloal conductivity(» ohos/cm)

JTitrogon (<£)

AvaUahl* ?J)C

nSiity?1ay

1.18

8.004»

0.108

91A.O

•*2 3Silty SUlyclay ct%;/loam }*>vn

1.32 1.21

.

•» «•

o.oo/r o.o?>?20.0 7.0

4Siltyclayloan

1.18

-

.

0.0^52.0

1Siltyclayloam

1.22

o.Ot)

2.05

0.089

?7.^

' 2Siltyclay

J.298.1

1.12

0.03?

:3.4

3Silty61 ay

:.r.5.7

i.87

0.031

*3.0

Silty

8.0

C-8 nr.. c -1^ cw, d, « 17-24, 25-32 cm

Table To. Some of the characters of the varieties used for root distribution studies.

3t

Pedigree1

Ig-8Introductionfrom IRHI, hybridselection from «cross betweenPeta x Dee-gee-wu-genTaichun* Native I

Plant type——— TJT — * ————

Semi-dwarf(80 cm)upright anddark greenleaves

Duration' 3 "

Photoinsensitive,130-135. days

Yield4

On an aver-age yieldsabout 6500kg/ha (with100 kg/fr/ha)

Grain Character5

3o2d, chalky,tolerablecockingquali fcy.

Disease r«»siatsr»3ef>

Susceptible to bias1and tungro moderate??susceptible to blight.

Introduction fromT«iw»m, Cross pro-duct using dwarf-ing g«ne dcn.ir,

-ohun X

130Tt is « selectionfrrra th«» localvariety in T?rrthIndia (selection

o at

Semi-dwarflittle reducedheight as aon-par«»d to T3-8and lees .larkgreen foliage

7«ry. t«'-ltmnr*»than 140 cm inheight, loss

Photoinsens itive,120-125 On an aver-age yieldsabout 5000kg (with 100kg N/ha)

K«?diura-, non-chalky cookingquality betterthan IR-3

Photosensi n\ve,120 d5;;s

synchronizedhead ing, lodging,

On an aver-age yieldsabout 3000kg/ha (with60 kg/R/ha)

s?lendernon-chalky,translucent,good cookingquality.

Highly sus^eptiol*to bacterial bligirtwufrr and mod:>rat! lysusceptible tc

tcthree dise33»s. He

Table Ib continued,

Selection fromthe selfedpopulation fromfive successfulback crosses ofTaichung NativeI X Basmati 370where Basinati-3?0 was uso'3 asa recurrentparent

3C 6Same as 3C 5

Semi-dwarf75 c veryupright, darkgreen

Photoingensitive,120-125 days.

Same as 3C 5 Photoinsensitivfi,110 days

On an averageyields 5500 kg/ha (with 100kg N/ha)

Medium selend»r,non-chalky,havingaroma, goodoooking quality

Moderatelysusceptibleto blight.

On an averageyields about5000 kg/ha(with 100 kg N/ha)

Same as BC 5 Same as BC 5

32 3?Percent injected P in different -vrts of the plant after 1, 3 and 6 days of injection ( "P injected with andwithout sucrose)

Cays after InjectedInjection tiller

Sucrose No sucrose1 89.5 90,1

3 89.3 88.8

6 88.0 88.7i—4to1

Dhxnject-nd Footstillers

Sucrose No sucrose Sucrose ?To sucrose-7.6 7.2 2.9 2.7

8.8 10.0 1.9 3.2

8.6 9.9 3.4 1.4

Tnblc Til

Spf.-aific nn

Root length

(in om)

0-5

5-1 D

10-15

>5

0-55-10

>10

fciv i ty (<

H

2396

121.7

873

• 1530

278

106

™nts /:.-•*

1 do

R2

1706 1

442

/387

18M'

604

285

?/••«' ".ut-. } of :iiff"r«nt r-H.-r. parts (P inject

iy 3 days(with sucroao)

rj D "D T5 TJ"3 Ri 32 R3 Bl

363

41 fi

296

8.50 .

282

187

972 "i6r>8

50] 1489

22'i 452

(without

415 608

189 370

223 2SO

434 . 3267

136 4498

67 3699

2.1

sucroso)

1370 1246

893 1176

832 1288

'•<\ w i r . t i and. w i t n c u l

6 days

748 2740

767 2877

872 2912

'•1575 1938

1484 1711

1382 1962

L = replicate 1, R- » replicate 2, : B3 s rePl^ca*e 3.

Table IV: Per cent root activity (by P uptake) of paddy variety TaichungNative I at different depths and lateral distances at floweringstage (by 2p placement in capsules)Date of transplanting:

32Date of P placement:Level of activity:

Location:

July 31, 1968August 15, 1968200 uc/plant (placed at fourpoints on the circle around theplant in the concerned zone).14, Main Block, Agronomy Farm,I.A.R.I. Delhi.

A Specific activity data ( punts/rag P/Sec for each zone)L1(2.5 cm)

d-j (4 cm) 125.3d2 (12 cm)d, (20 cm)d (28 cm)Total

30.419.711.3186.7

L = Lateral distance from thed = Depth, where

io root activityI

d-j (4 cm)dg (12 cm)d, (20 cm)d4 (C8 cm)Total

LateralS.BnC,D. at 5$

L2 (12.5 cm)52.829.716.011.3109.8

plant where

i L (22.5 cm)14.013.75.02.335.0

capsule was put.

Total192.173,840.724.9331.5

the capsule was placed.

\ (2.5 cm)37.59.15.93.456.4

L2 (12.5 cm)15.88.94.83.432.9

F test significant at 1$distance (L) Depths (d)0.571.17

0.691.81

L3 (22.5 cm)4.24.11.50.7

10.5

Interaction1.142.35

Total57.522.112.28.0

99.8

- 74 -

Table V: Percentage root distribution (by counts).of some paddy varieties at different depths and lateral distancesat flowering stage. (Using carrier-free P injection technique).

Year 196? Year 1966Date of transplanting: July 31, 1967 July 31, and August 1, 1968Date of 32p injection: October 27, 1967 October 25, 1968Level of activity used: 5°0 uc/plant 5°0 uc/plantLocation: 14 and 15 Main Block, Agronomy Division Farm, I.A.R.I., Delhi.

Taichung Native I (196?)

dlfj£"3a4

A.[0-8 cm)(9-l6ctr(17-24(25-32

i)cmcm

Total

Percentage root distributionL,(2.5 cm)

45.720.4

) 6.3) 5.6

78.0

L?(12.5 cm) ]9.93.31.71.716.6

by counts.L, (22.5 cm)9 2.4

1.11.10.95.5

B.Total58.024.89.18.2

100.0F test significant

Lateral distancess.mC.D at 5

1.6& 3.2

depths1.93.9

Taichung Native

dd2d.'V

(0-8 cmA.

)(9-16 cm)(l7-24ci(25-32cim)

Total

Percentage root distributionT., (2.5 cm)1 41.8

14.73.52.062.0

by counts.LJ12.5 cm) L^ (22.5cm)2 16.6

5.94.41.828.7

" 3.01.62.32.39.2

B.Total ~~61.422.210.26.199.9

Net countsL.. (2.5 cm)62.3340.5105.093.5

1301.3at I**?

per 500 seconds.L (12.5165.055.0

28.528.5277.0

cm) L, (22.540.018.518.15.92.

500

cm) Total967.3414.0152.0137.01670.3

Interaction

I (1968)

3.16.5

Net counts per 500L,(2.5 cm}1491.0524.5125.071.5

2212.0

1 L?(12.5592.0210.015f.O64.0

1023.0

seconds.cm) L,(22.5

107578282328

.0

.1

.0

.0

.1

cm) Total2190.0792.1364.0217.53563.6

F test significant at 1%S.SdC.D

Lateral1

at 5<£ 3distances.90.92

depths2.294.73

Interaction3.7.8084

Table V. continued

!•

did9d*d4To1

Percentage root

0-8cm)9-l6cm)17-24cm)25-32cm)Sal

L,(2.5cm)61.910.73.82.8

79.2

distribution (by counts)

(I2?5cn)4.94.62.11.615.2

L^ Total(22.5cm)3.1 69.91.6 16.91.6 7.51.4 5.87.7 100.1

HP 130 (1968)

B* Net counts per 500 seconds.Li(2.5cm)

d,(0-8cm) 1933.0d2(9-l6cm) 334.0d (17-24cm) 118.5d (25-32cm) 87.5Total 2473.0

(I2.fcm)153.0143.565.550.0412.0

(22 5 cm)97.050.050.043.5240.5

Total

2183.527.234.1.8 1.3125.

05005

'P* test significant at 1Lateral distances

S.Hi 1.03C.D. at 556 2.13

A« Percentage root

d. (0-8cm)d (9-l6cm)d*(!7-24cra)d (25-32cm)Total

Li(2.5cm)44.611.74.33.864.4

distribution (by counts)L2(1275cm)11.25-63.81.522.1

S.EdC.D. at 5

L.J Total(2275cm)5.3 61.12.8 20.13.3 11.42.1 7.413.5 100.0

»P» testLateral distances

1.402.90

Depths Interaction1.24 2.062.57 4.26

IR 8 (1967)B_. Net counts per 500 seconds

Ll(2.5cm)d1(0-8cm) 266.5d«(9-l6cm) 70.0df(\7-24cm) 25.5d (25-32cm) 22.5Total 384.5

significant at V&

L?(12.5cm)67.037.522.59.0

132.0

(22.5*em)31.516.519.513.080.5

Total

365.0120.067.544.5597.0

Depths Interaction1.77 2.903.60 5.90

.A. Percentage root distribution by counts.L,(2.5 cm)

d.(0-8cm)df(17-24cra)d ( 25-3 2cm)Total

36.46.25.82.050.4

S.SdC.D.

Table V. continuedT"? 5 (1968)

B_. Net counts per 500 seconds.12(12. 5cm) L (22«5cm) Total L,(2.5cm)

20.06.24.13.0

33.3

Lateral1.

at- *Wt \Cl U V/v 3 •

7.63.62.92.216.3

•F* testdistances5009

64.016.012.87.2

100.0significant at

depths1.813.73

936.4159.5149.251.31296.41$

L0(l2.5cro) L>(22.5cro)C, j

514.5159.5105.577.0856..5

195.592.574.556.5419.0

Total1646.0411. C329.2184.82571.9

interactions2.996.18

BC 6 (1968)A-did*

Percentageh

(0-8cm)(9-l6cm)fl7-24cm)

Total

root distribution by(2.5cro) L2(l2.5on)45.5 14.94.3 5.31.8 3.34.4 3.656.0 27.1

counts. B.L3(22.5cm) Total ~"9.0 69.44.1 13.72.0 7.11.8 9.816.9•P' test

Lateral distancesS.BdC.D at C0£s •

1.723.54

100.0significant at

depths2.074.27

Net counts per 500 seconds.L1(2.5cm) L2(l2.5cm) L.J1625.0 532.0153.0 189.064.0 118.0157.0 128.51999.51*

987.5

'22.3211467164604

5cm).5.5.5.5.0

Total2478.5489.0253.5350.03571.0

interactions3.437.08

L » Lateral distance from the plantd « depth of sampling

Table TI.Percentage r-'Ot attribution pattern (by counts) of ?:iichung Hative I variety of paddyas affected r,y different levels of Nitrogen (As trrt?'./, (Using corrier-frer> 32p plantinjection technique).

Date of transplanting!Date of *2P injectionsLevel of activity injected*'Locations

July 31, 1967October 27, 1967500 uc/plant15, Main Block, Agronomy Division Farm,IARI, New Delhi.

CONTROLA.. Percentage root distribution by counts.

<j^9dfd4

0-8cm)9-l6cm)17-24cm)25-32cm)

Total

L2 (2.5cm)40.07.63.72.9

54.2

L2(l2.5cn13.75.44.54.5

28.1

i) Lj (22.5cm5.14.94.13.6

17.7

) Total58.817.912.311.0

100.0*F* test signific

Lateral distances

A.

d-. idv

Percentage1

0-8om)9-l6cm)17-24cm)

d*(25-32cm)Total

S.'SHC.D. at 5<

d -

root distribution byLj (2.5cm)

36.013.85.84.5

60.1

L2(l2.5cn)6.46.14.64.1

21.2

0.961.98

depth t70

counts.L.(22.5om)

5-33.84.74.9

18.7

depths1.162.38

L * LaIteN/ha

Total47.723.715.113.5

100.0

B. Net counts per 500 sec-nds.Lx(2.5cm) L2(l2.5om)

672.3 230.2127.7 90.862.2 75.f48.7 75.7

910.9 472.4at 15&

Interactions1.923.96

Lateral distance

2» ffet counts per 500 seconds,L1(2.5cm) L2(!2.5cm)

402.0154.264.850.2

» -C.D at 5*

•P' test significant atLateral distances depths

1.57 1.893.24 3.91d « depth t

671.2

Interactions

71.568.251.345.8

236.8

L3 (22.5cro )85.782.368.860.5

297.3

L3(22.5cm)59.242.552.554.7

208.9

Total988.2300.8206.7184.9

1680.6

Total532.?264.9168.6150.7

U16.9

L - Lateral distance

Table VI. continupd

A*

dld?dfd4

Percentage root distribution1^(2.

(0-8cm) 42(9-! 6cm) 17(17-24CK;) 3(25-3 2cm) 2

Total 65

A-

d'it>-ri?d4

5cm) L?(12..0 7.2.0 4.5.4 .1.5.7 5.2.1 2? .4

S.WC.P at 5"5

Percentage root distributionL'l^2*'

(0-8cm) 35.4(9-l6otn) 31.8(l7-24em) 2.?(25-32cm) 1.4

Total 70.8

5cm) L2(12.'

9.92.82.02.2

16.9

S. SriC.D. ft

by counts.5om) L-,(22.5om)

2.24.23.73.4

13.5»?• test

Later?.! distances0.891.83

d - depth

by counts.5cn) L.j(22.5cTn)

4.63.22.42.0

12.2•F« ten*

Lateral distances0.86

5^ 1.78d = depth

140

Total

5^ .425.711.631.3

100.0signif ic.-int

Dep ths1.072.21

L = Lat<21.0

Kg N/ha

B. Net counts p»r 5L3 (2.5cm) L?(12.

667.8 114.270.3 71.54.0 71.42.8 82.

103/1.9 340.at 1<

Interactions1.783.67

L-r«l dista.nces.!fc IT/ha

iOO seconds •5cm) L,(22.5

5 35.05 66.85 56.87 54.02 214.6

B. Nt-t counts por 500 secondsTotal

49.937.86.65.6

99.9signif A cant

Depths

1.042.14

: L

L1 (2.5cm) L?(12.923.3 258.2829.5 73.057.3 52.236.5 57.5

1846.6 440.9at 1^

Interactions1.723.55

= Lateral distances.

5r:m) 1^(22. 5<120.088.562.752.2

318.4

Total817,408.184.179.1589.7

Total1301.5986.Q172.2146.?2605.9

SCHEMATIC SKETCH SHOWING THE PERCENT ROOT DISTRIBUTION (BY COUNTS) IN DIFFERENTSOIL ZONES OF SOME OF THE PADDY VARIETIES AT FLOWERING STAGE. (CARRIER FREE P32

PLANT INJECTION TECHNIQUE)

DATE OF TRANSPLANTINGDATfci OF P32 INJECTIONLEVEL OF ACTIVITY USEDLOCATION

I96TJULY 31OCT.2750O JJC/PLANT10 MAIN BLOCK

1968JULY 31 AND AU6. IOCT. 25SOO .DC/PLANT14 MAIN BLOCK

AGRONOMY DIVISION FARM I. A . R . I . DELHI

TNI1967 TNI1968 IR-8 1967

«•« aa-e •»•« 22 5 22-9 tt-9

us>a PERCENTAGEg TOTAL

ACTIVITY

LATERAL DISTANCEStem) LATERAL DlSTANCESl cm.) LATERAL DlSTANCEStem.) 0-5%

NPI30 1968 BC 5 1968 BC 6 1968

22-9 12-9 tt-9 aa-9 22-9 12-9

LATERAL DISTANCES! cm) LlfTERAL DISTANCES (em) LATERAL WSTANCESCcm.)

t ROOT DENSITY SHOWN IS APPROXIMATELY PROPORTIONAL TO THE PERCENTAGE OF TOTAL ACTIVITY )

- 80 -

SCHEMATIC SKETCH SHOWING THE PERCENT ROOT DISTRIBUTION(BY COUNTS) IN DIFFERENT SOIL ZONES AS AFFECTED BY DIFFERENTLEVELS OF NITROGEN OF PADDY VARIETY TAICHUNG NATIVE I AT

FLOWERING STAGE (BY CARRIER FREF P** PLANT INJECTION TECHNIQUE)

DATE OF TRANSPLATING——DATE OF P32 INJECTION —LEVEL OF ACTIVITY USED-

LOCATION

JULY 31, 1968OCT. 27, I960

500 pC/ PL ANT

14MAIN BLOCK,AGRONOMY DIVISION FARMI. A. R. I. DELHI.

CONTROL 70 KG N/ho

PERCENTAGETOTAL

ACTIVITY

JO-5%

5-10%

10-15%

15-25%

25-35%

95-45%

LATERAL OISTANCES(em.)

WO KG N/ho

125 22 5

LATERAL DISTANCES(cmJ

atO KG N/ho

B-522-0

LATERAL DISTANCESfCm.) LATERAL DISTANCES (em.)

(ROOT DENSITY SHOWN IS APPROXIMATELY PROPORTIONAL TO THE PERCENTAGE OFTOTAL ACTIVITY)

- 81 -

THE EFFECT OF OSMOTIC PRESSURE ON P-PHOSPHATE ABSORPTIONAND LEAKAGE BY EXCISED RICE ROOTS AND THE ADAPTATION

OF RICE ROOTS TO VARYING OSMOTIC PRESSURESSMeh, Yuh-Jang, Institute of Botany, Academia Sinica, Nankang,

Taipei, Taiwan, Rep. of China

ABSTRACT

32The amount of P-phosphate absorbed by excised upland rice roots decreasedwith increasing osmotic pressure of the solutions. This trend was less markedfor paddy rice roots. If active absorption was expressed by the amount of ionstaken up into the cells and maintained therein against loss, the ability of ionaccumulation of both paddy and upland rice roots was greatly reduced by highosmotic pressure of the solution.

Rice roots adapted to high external osmotic pressure by increasing internalosmotic pressure and dry matter content. This adaptation enabled rice roots toaccumulate phosphate from solutions of high osmotic pressure as well as fromhypotonic solutions.

Plasmolyzing rice roots absorbed phosphate actively as well as turgid roots.The absorption can be effectively suppressed with 2,4-dinitrophenol.

Large amount of phosphate exosmosis was induced by immersing plasmolyzedrice roots into solutions of low osmotic pressure or water. The amount and therate of phosphate leakage were proportionately related to the rate of water entryinto the root during deplasmolysis. This leakage was considered to be essentiallya process of diffusion having a Q,Q of 1.3 in the temperature of 20-40 C.

Loss of the dry matter of the root always accompanied phosphate exosmosis.After the period of exosmosis, a deplasmolyzed rice root reabsorbed and accumu-lated phosphate at a steady but lower rate than the normal root.

A new method for determining the osmotic pressure of plant tissues bydetecting solute leakage was suggested.

- 82 -

THE EFFECT OF OSMOTIC PRESSUHE ON 3 P PHOSPHATE ABSORPTION ANDLEAKAGE BY EXCISED RICE ROOTS AND THE ADAPTATION OF RICE

ROOTS TO VARYING OSMOTIC PRESSURESYuh-Jang Shieh and Teh-Chien Shen

Institute of Botany, Academia Sinica, Taipci, Rep. of China

1. INTRODUCTION

The forces involved in the transfer of water from soil to plant roots maybe attributed mainly to the hydrostatic pressure and the osmotic potential ofsoil water (Day, 1942). In general, plant growth is retarded by a high moisturepotential of the soil. Successful crop production was found on soils which hadthe osmotic pressure (OP) of 4 atm or less.

The major factors which affect the OP of plant tissues were soil moistureand humidity (Stoddard, 1953 and Herrick, 1933). Increased drought conditionsresulted in an increasing osmotic value throughout the aerial parts of the plants.A measurement of the osmotic values was a reliable index of the relativepotential ability of a plant to compete for water under conditions of stressand due to a deficiency of water.

The requirement of metabolic energy for the accumulation of ions by plantroots is well documented in published literature. Anaerobiosis, uncorplersof energy transfer, and inhibitors of respiration have all been shown to inhibition uptake* It has generally bcf-n considered that metabolic energy is requiredfor the transport of ions across cell membranes.

All plant parts and especially thin sections derived from them have beenobserved to leach solute upon immersion in water or rinse under water. Inrecent years evidence that the permeability of cell membranes may be modifiedby unfavourable conditions has benn presented, A large amount of exosmosis ofcell constituents was found to be induced by inorganic salts and organic sub-stances. Helder (1956) mentioned that phosphate and other inorganic salts wereusually present in the exduate of roots and other plant tissues along witheasily diffusible parts of the cell constituents as the consequence of increasedpermeability of cell membranes induced by salts, toxic materials or metabolicinhibitors.

32This paper presents the data, concerning the absorption and loss of P-phosphate of excised rice roots as affected by the tonicity of, the externalsolutions and the adaptability in nutrient absorption of rice roots to theosmotic pressure of external solutions.

2. MATERIALS AND METHODS2.1 Preparation of root materials.

Seeds of a paddy rice variety, Taichung No. 65, were soaked in tap water at28-30 C for two days. When the seminal roots started to emerge from the husk,the seeds were spread on a layer of cheesecloth which was supported by analuminum frame of 15 cm in diameter. The frame was set on a large petri dish.The corners of the cheesecloth were dipped into the water in the dish. Asecond cheesecloth was spread over the seeds. The roots wore grown at 28-30 Cin the water underneath the cheesecloth. Roots were excised just below thecheesecloth when they attained the length of 2-3 cm.

- 83 -

2.2. Absorption experiments.Two mM KHpPO. solution was prepared for the absorption experiments. The OP

of solutions was idjusted with mannitol. Excised roots were rinsed with distilledwater, and gently blotted on dry soft lintless paper. One gram samples wereweighed out and transferred to a 250 ml Erlenmoyer flask. Ono hundred ml of theexperimental solution was then poured in. Radioactive phosphate was added intothe flasks at the beginning of the absorption period. The solution had a pH ofabout 4.2-4.5- The solution was vigorously nerated and was kept at 30 C. Afterthe absorption period, root samples were separated from solution with a copperscreen, rinsed with 300 ml of water, spread evenly in planchets and dried at 40 C.2.3. Exosmosis experiments.

Two grams of excised rice roots wore allowed to absorb phosphate for 3 hoursin 2 mM KH0PO. solution which was labelled with radioactive phosphate. The rootswere then treated with solutions of different osmotic pressures. Pbcosmosis ofphosphate remaining in the root after the treatment or by the amount of radio-active phosphate leaked out of the root into the external solutions. In the lattercase, 0.1 ml aliquot of the external solution was drawn at different times dmringthe treatment for radioactivity counting.2.4. Paper chromatography.

Qualitative studies on the phosphate compounds in rice root and those leakedfrom the root were carried out with a paper chromatographic technique. The 80$ethanol extracts of rice roots or its leakage was spotted on Whatman No. 1 filterpaper. The chromatograms were developed one-dimensionally using butanol-propionicacid-water (10:5:7 v/v).

3. SHORT-TERM ACCUMULATION OF 32P-PHOSPHATE BY EXCISED RICE ROOTS

Plant roots absorb ions in two phases: the initial rapid absorption andfollowed by a linear stable uptake. The second phase is defined as active uptakewhich is ai energy require process. Rice roots absorbed phosphate in the similarmanner.

32Figure 1 shows that excised rice roots absorbed P-phosphate in a series ofexternal osmotic solutions adjusted by mannitol. Mannitol was chosen as theosmotic agent. Ferguson et al, (1958) reported that mannitol could be classifiedas unable to function as a carbon source for tomato root culture. It was foundthat little externally-applied mannitol .-;ntered into potato discus (Thimann et al.,I960). Roots which only washti with 300-ml of water for 5 seconds after absorptionabsorbed phosphate as the same in all osmotic pressures while roots which soakedin six changes of 200-ml of wat&r in an ono-hour poriod caused a groat decrease inphosphate absorption at higher osmotic pressures. "Burg ct al. (1964) reportedthat a high concentration of glyccrcl or other osmotic agents prevented exosmosisfrom those tissues. It is shown that rice roots maintained a great portion of theabsorbed phosphate during plasmolysis. Dut when plasmolyzed rice roots wereimmersed in water, a great portion of the- absorbed phosphate leaked out of the roots.The phosphate uptake was decreased as the external osmotic pressure increased. -

Mere interest was in the uptake of phosphate- by both turgid and plasmolyzingrice roots (Fig. 2). During the first 30 minutes, rice root absorbed morephosphate in the solutions containing 0.4M cf mannitol regardless of the presenceor absence of DNP. This increased rate of phosphate absorption by the plasmo-lyzed root:', may be attributed to the increased volume of free space. Plasmolyzingrice root accumulated phosphate ions metabolically, though at a lower rate thanthat of the turgid root, Active accumulation was effectively inhibited by thepresence of lxlO~4}i DNP in the absorption solution.

- 84 -

4. LEAKAGE OP 32P-PHOSPHATE AS AFFECTED BY SALTS, OSMOTIC AGENT, AND METABOLICINHIBITOR

When rice roots wore treated with consecutive soakings in water and 0.4 Mmannitol solution, a great portion of the absorbed phosphate was lost from theroots if the roots were plasmolyzed first in 0.4M mannitol solution and worethen transferred to witcr (Table l). Measurements of the radioactivity in theexternal solutions showed that a small amount of absorbed phosphate was presentin the mannitol solution while a great amount of phosphate was present in thowater when the plasmolyzed ro--ts were transferred to it. Further work showed thatrice root plasmolyzed in the hypertonic solution of inorganic salts (NeCl+Na2SO.)resulted in a great loss of its phosphate when it was transferred to water.Polyethylene glyool (C20M) solution of the concentration of 22.8$ by weight whichwould have an osmotic pressure of about 10 atm. as determined with thermocouplepsychrometer method by Lagcrwerff et al. (1961) induced neither appreciableplasmolysis nor great phosphate leakage cf rice root.

It was noticed that e loss of dry matter from the root always accompaniedthe leakage of phosphate (Table II). .The data which did not list also showedthat high concentration of DNP (5xlO~ M) caused a loss of dry matter.

The data presented in Table III show that rice roots plasmolyzed in 0.5Mmannitol solution lost more phosphate when they were subsequently soaked in water(M5-0). Plasmolyzed rice roots lost more phosphate into the water (M5-0, M3-0)than into 0.2M mannitol solution (M5-2, M3-2). These data suggest that theleakage of phosphate is proportionally related to tho degree of plasmolysis ofthe root and the rapidity of water entry during deplasmolysis. The experimentalresults summarized in Table IV indicated that when the concentration of theexternal solution was first gradually diluted from the 0.4M solution to 0.2M, theplasmolyzed root lost less phosphates than when it was directly transferred fromthe 0.2M solution to water.

An example of the time course of phosphate leakage from plasmolyzed root intowater is shown in figure 3. In all of the cases studied, the initial rate ofphosphate leakage and the time needed for reaching equilibrium were affected bythe difference between the osmotic pressures of the solutions of consecutivesoakings and the amount of absorbed phosphate in the root.

The phenomenon of the leakage was furthor studied by measuring the rate ofphosphate exosmosis at different temperatures in the range from the freezing pointtc 40 C and in the solution^of different non-radioactive phosphate concentrations(Fig. 4). In the temperature range of 20-40 C, the rate of phosphate leakage wasa linear function of temperature with a temperature coefficient of about 1.3,typical of a diffusion process. However, the rate curve flattened between 10 and20.C, and rose when the temperature was approaching the freezing point. The ratoof phosphate leakage was not affected by the presence of the same ion species atlow concentrations in the external solution. However,, it was somewhat increasedwhen the concentration of phosphate in the external solution reached 2-20 mM. Itis speculated that the phosphate leakage is essentially a diffusion process. Itsrate was enhanced near the freezing point by the changes in certain physicalproperties or the consistency of tho cytoplasm (Seifriz, 1936). The increasedrate of phosphate leakage observed in 2 and 20 mM KH^PO, solution may be due tothe isotopic exchange facilitated by the high concentration of non-radioactivephosphate in the oxter solution.

* -85-

Paper chromatographs (Pig. 5) showed that after ther three hour period ofabsorption, a large portion of the absorbed phosphate remained in the form ofinorganic phosphate. Six other labelled unknown compounds were found. Radio-isotope labelled phosphate compounds which leaked out from a deplasmolyzingrice root were mainly inorganic phosphate and four othor unknown It was evidentthat solute leakage.- induced by dcpiasmolysis was not n result of complete disorga-nization of the proplasm or the membranes.

5. ADAPTATION OF RICE ROOTS TO VARYING OSMOTIC PRESSUREf

The degree of the damage that a rico root was subjected to during deplasmo-lysis was studied by observing the recovery of its phosphate absorption ability.One-gram samples of rice- root were plasmolyzod in 0.4M mannitol solution for 1hour, rinsed to remove the mannitol adhering on the root surface, and then trans-ferred to 2 mM KHpPO. solution containing radioactive phosphate. Differentsamples were taken f?om the absorption solution at given times, soaked with 4changes of 200 ml of water within one hour to remove the phosphate which was notactively absorbed by the roots. The results (Pig. 6) showed that after the first30 minutes to an hour of immersion in the absorption solution, deplasmolyzingroots started to accumulate phosphate at a steady but lower rate than that of th<=normal rice root. This steady phase of absorption continued to the 12th hour atthe end of the experiment while the absorption of a normal root was a linearfunction of time for about 7 hours and continued to absorb phosphate at adeclining rate from the 7th to the 12th hour.

Further experiments wei^e conducted with roots grown in solutions of differentOPs. Roots designated as RMO were gr»wn in water. R,^ roots were grown in waterfirst, then transferred to-a mannitol solution of the OP of 4.97 atm for 1 day.RM. roots were further transferred to mannitol solution of the OP of 9.94 atm foranother day. R.. roots acted similarly to the roots of figure 1. R.,- and R.,.roots absorbed considerable amount of '•P-phosphate from the external solutionsof the OPs of 9*94 and 12.43 atm (Fig. 7). RMQ started to plasmolyze in the testsolutions of the OP of 7«46 atm. P-.p roots plasmolyzod only slightly in the testsolutions of 12.43 atm OP. R.,. roots kept turgid in rill of these test solutions.Roots grown in solutions of high OP had more dry matter in the one-gram fresh rootsamples than those grown in water or solutions of low OP. Average day weight ofthe samples of RMQ> M2' an< %I4 roo*s Were 64.9» 61.7, and 93.7 rog respectively.

32Two sets of RMQ and R... root samples wore prefed with P-phosphate in2 mM KHrtPO. solution. The samples wei-fc washed with 300 ml of water and thenimmersed in raannitol solutions of different OPs for two hours. The roots wereagain soaked in wat^r for^an hour before drying and counting. It was found thata great amount of prefed P in the samples treated with mannitol solutions ofhigh concentrations was lost from RMQ roots during the soaking period. The amountof 32p remained in these roots (Fig. 8) was closely similar to the accumulationcurve of R...- in figure 7. On the other hand, the amount of prefed 32p n -a rootswas not afrooted by the immersion into mannitol solutions.

It was evident that rice roots acquired the adaptability of growth andabsorption in iso- or hypcrtonic media. The adaptation was manifested by theincrease in dry weight and 32p accumulation from solutions of high tonicity.In the intact rice roots, reserve materials from seods might serve as a sourceof osmotic active materials i'n<•• addition to those released by the root cells.The increased OP of protoplasm enabled the cells to keep turgid in solutions ofhigh tonicity. This is believed to be essential for ion accumulation in rice roots.

- 86 -

6. A NEW METHOD FOR DETERMINING THE OSMOTIC PRESSURE OP PLANT TISSUESExperimental evidence showed that phosphate exosmosis accompanied the depla-

smolysis of the cells. It offers a possibility of determining the osmoticpressure of plant tissues by detecting solute leakage when incipient plasmolysiscannot be seen clearly in the plant tissues such as rice roots. Rice rootsamples prefed with radioactive phosphate were soaked in mannitol solutions ofdifferent concentration for one hour and then transferred to water. It was foundthat the roots which had been treated with mannitol solutions of the concentrationhigher than 0.22M lost appreci'.'ole amount of phosphate. The amount of phosphateloss increased sharply as the concentration of mannitol solution increased from0.24 to 0.40M (Pig.9). The OP of the cell sap of the rice root was 0.23M asdetermined" with a cryoscopic method. The value was very much the same as thatindicated by the transition point of the curve in figure 9»

REFERENCES

(1) BURG, S.P. et al., Relationship of solute leakage to solution tonioity infruits and other plant tissues, Plant Physiol. 39 (1964) 185.

(2) BURG, S.P., THIMANN, K.V., Studies on the ethylene production of appletissue, Plant Physiol. 3_5_ (i960) 24.

(3) DAY, P.R., The moisture potential of soil, Soil Sci. £4 (1942) 391.(4) FERGUSON, J.D. et al., The carbohydrate nutrition of tomato roots.

V. The promotion and inhibition of excised root growth by various sugarand sugar alcohols, Ann. Bot. 22_ (1958) 513.

(5) HELDER, R.J., The loss of substances by cells and tissues (salt glands).In: Ruhland, W. (ed) Ency. Plant Physiol. 2_ (1956) 468.

(6) HERRICK, E.M., Seasonal and diurnal variations in the osmotic values andsuction tension values in the aerial portions of .Ambrosia trifida,Amer. J. Bot. 20 (1933) 18.

(?) LAGERWSEFF, J.V. et al., Control of osmotic pressure of culture solutionwith polyethylene glycol, Sci. 133 (l96l) I486.

(8) SEIPRIZ, W., Protoplasm. McGraw-Hill, New York (1936).(9) STODDARD, L.A., Osmotic pressure and water content of prairie plants,

Plant Physiol. 10 (1953) 661.(10) THIMANN, K.V. et al.. Penetration of mcinnitol into potato disks, Plant

Physiol. 3£ (i960) 848.

Table I. The /«.«.< of absorbed fhasphalc /»»»» rice n»'ts MX cauwl by n HsrralircsuaAi'n#s I'M water an-l O.IM »;tinntl»l st

Tr«-atmci«*

* out rot i

A

B

1** |»l;<>s)»hatr rein:;ii>>niin ri-«.t. ;•« «>l «-<>ntr*rl

t«t.O

C i_

i**nzifc"***T

_..)97.5

D t- z/.r,

P L. ...rrrm:x:r_r..:* I i t ato<>rptiun•••• m*nninti.<l 0.4M

water

IL r*« /on </ dry tnatttr and absorbtd phosphate info wattr fiont ttctroots ptosmatyted previously in different hypertmic solutions

Treatment

control•»lt» a4Mmannitot tt4MC20M ZZ»%

Dry wt. of rixit aftertreat m«nl, •. at iiouirol

loao9028a9

102L7

>'" phosphate remaining inroot, fi of control

100.0&4£33.487.1

' ..fole ill. The lass t>f abstwhcil phosphate fr<im rice root an caused by consecutives(.akint; in mention* <>f Jifi'frrnt hmtrilirs

Treatments*

M5-0

in r«v.t. ".,' of roritn.l

11)0.0

34.3

M3-0 » ——— -! ——

M3-2 < ———— •*— •

W t J- -

1 IS \ ^ y^ - ——— -^ *.•» -.

!

( | —— — .r: _~ ~~i 01 \

* 1 —— _ —— i . ih : i>r j ) l i<in I 1 I 1 1 1 in:uinit»l (U'M••••I m.innitol H.'i.M __ w;itt".i x x s x v v mannilol 0.3M

Table IV. The loss of alwrbrd phosphate from >ifc tmt as aflecttdby the fate of

Period for rlianRincdown from C.-1 to O.^M

mannitol solution(hr.)

1st experiment8420*»

2nd experiment44440"

Intfrva! betweensuccessive additions

of water(min.)

6030ir»—

153060

120m ~

Di'iicaS' 111 theioni'«'iitirt(ion of

manti i t i i l solutionrnuscU by eaih

addition of water(M)

0.0250.0250.025

"0-01250.0250.050.1

~

P*1- phosphateremaininR in the

root (';i of cuntrol)

" '" ' "

45.939.235.623.9

56.153.848.743.328.4

* Kice roots were prefed with phosphate and then soakrd in 0.4M mannitol solutionfor 1 hour. Afterward, the concentration of (he niunnitnl solution was diluted atdifferent rate from P.4 to 0.2M by ir.eans of adding water as indicated in the table.The roots were transferred from 0.2M mannitol solution to water and were stakedtherein far 1 hour.

*• Kcots directly transferred from 0.4M mannitol solution to water.

_ or, _

3000

9 Ot.JSmo> o>o ».

2000

1000

01fto

8 10Osmotic Pressure (atin)

Fig. 1. Absorption of P -phosphate by roots in solutions of differentOPs. x , roots washed with 300 ml of water for 5 seconds afterabsorption, c , roots soaked in 6 changes of 200 ml of wat rin one hour period.

- PI -

<D O

^"3, coO 4>tf> (-,

or ociL

l^-l J^

o u>

IIO 0i

fc.Orx -

120Time in min.

i8C

Pig. 2» The absorption of phosphate by excised rice roots in 2 mMKHgPO/j solution with or without the presence of DWF andjnannitol.* , without mannitol; x, with 0.4 M mannitol; -,without DNP; •••, with 10" f DNP. Roots which were usedfor the DNP t.»atments were pretreated with lxlO"*M DNPfor 30 minutes before the absorption period.

60 12UTine In min.

100

Fig. 3» The leal-cage of absorbed phosphate into eacternal water fromroots plasiaolyzed previously in -lifferent hypertonic solutions.

goa*

Si

8C

60

o

20

10 20 30Temperature CO

40 O.C2 0.2 £ 20KHjPO, concentration. mM

Fig. /». The rate of leakage of absorbed phosphate from plaamolyzecL riceroot as affected by temperature (left) and the concentration oiphosphate in the external solution (right). The rate pf leakagwas expressed by the amount of phosphate leaked from the root;into the external water or KH2 0 solution during the first 10minutes of soakjng.

o o

0 0 0o oQOrigin

Re R E5» Autoradiograph of a paper chromatograph of the K.-

compounds in rice root and leakage. K and R,;, P" -labelledcompounds in root before end after the leakage induced byplasBolysis-deplasmolyais treatment. .The roots were groundand extractor dth 804 ethanol. B, i"" -labelled corapoundsin leakage, nie leakage was evaporated to dryness fnd re-dissolved in BQi ethanol for paper chrooatographing.

Is• Vi+» O

CM

»0,COO

8.00C

6,000

2,000XL--.- t _ - i—2 4 « • .10 12

Time in hourFig. P. The absorption of phosphate by untreated and MM^riM ric.

roots were plasnolyzed In 0.4 M mannitol solution and th ntransferred to 2 mH KHoPO solution for absorption. Sampleswere rinsed in water for 1 hour after they were taken fromthe absorption solution to remove the diffusible phospnajin the outer space. Untreated rice roots were used as thcontrol. • , control; O , plasmolywd roots.

^

t

Is.?aS&I

4000

3000

2000

1000;

0 2 4 6 6Osmotic Pressure (ata)

7. Absorption of P3 -phosphate by R«Q (•)»roots in solutions of different DPs. Roofwat r for i hour after absorption period.

10 12

*ndwere soak 'with

4000

3000 -

2000 -

1000 -

4 6 8 10Osmotic Pressure (atm)

12

Pig. 8. The loss of prefed P* -phosphate from H..Q (•) and 1L., (*)roots caused by 2-hour immersion in mannitol solutions ofdifferent OPs. The samples were soaked in 6 changes of «<•ml of water for one hour before drying.

M.OOO

30.000

»,coo

ao»ooor&M 0

«•! 0.2 00 OJk

Concentration of mannitol solution, MPig. 9. The loss of absorbed phosphate from rice roots which had U

immersed in mannitol solution of different concentrations •:on hour before being transferr d to water.

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EFFECT OP SILICON ON THE ABSORPTIONOP MANGANESE AND PHOSPHORUS IN RICE SEEDLINGS

Shim, Sang Chilj IT., Jang-Kirl} Lee, Hyong-KooRadiation Research "Institute in Agriculture

Office of Atomic EnergySeoul, Korea

1968

I. INTRODUCTION

Recent studies on silicon fertilizer have shown that application of silicatesunder certain conditions, have resulted in increased yield of rice crops (12,13, 19)« On the other hand, the close relationship of silicate applicationwith increasing resistance to insect pests, pathogenic fungi and lodging, haslong been recognized* Although a considerable attention has been -paid to anincreased yield, comparatively little is understood about its unique nutritionalaspect.

In the previous paper (20), it was shown that silicon affects the absorptionof both manganese and phosphorus by rice plants. At the low concentrations ofsodium silicate, as a source of silicon, the absorption peaks of the manganeseand phosphorus were found at the silicon concentration of 50 ppm.

In the present paper, effects of silicon, at low concentrations, on theabsorption of the two elements have been re-examined. For this .study, .sodiumsilicate and m-silicic acid have been utilized as the source of silicon.

II. EXPERIMENT

A) Material1) Rice varieties: Two rice varieties were chosen; one was Kwanok as a

lodging variety and the other Jinhung as a lodging-tolerable one.2) Seedlings: Test plants were obtained as follows:

a) Rice was germinated and grown in distilled water for 20 days in agrowth-cabinet, mod. YGC-125, controlled at 20°C, at the relativehumidity of 65-80$ and illuminance of 4,500 Lx.

b) Rice plants grown as a) were transplanted to 2.5 litre plastic potfilled with a complete culture solution*) and grown about a month in agreen house until just before tillering.

B) Treatment of Si, Mn-54 and P-32a) Silicon: Water glass NapSiO, and m-silicic acid**) were used. Solution

of 0,5, 10, 25, 50 100 and 200 ppm of Si were prepared and 500 ml of thesolution was used for treatment

b) Mn-54 and P-32: Mn-54 as MnClg ; 3.2 micro-curies / 500 ml, P-32 asEjPO. j 7.4 micro -curies / 500 ml.

c) Culture solution: 9 test plants, either 20 days or 50 days old, wereimplanted to a 500 ml beaker, and left for 3 hours. Each treatment wasmade 3 replications.

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C) Measurement of radioactivitiesAt the end of 3 hours incubation period, tissues were burned and ashes

were uniformly spread on counting planchet. Activities of the Mn-54 weremeasured with scintillation detector, type P-20P and P-32 with end-window(1.8 rag/cm^) Geiger tube.

*; The chemical constituents of the complete culture solution (the amounts of" nutrients in 5 litres as full strength)

Major elements

Ca(N03)2

Minor elements in Z-solution(per 1 litre solution)

n.Pe-EDTA

molittt(if t

mol

12.55 ml25 »10 "8 "0.05 "50.5 "

ZnSO.01130475 0H^BO,KI J

Co(N03)

0.2 gm0.18 »0.1 »0.50.03o.i

ftttti

**) m-silicic acid, H«SiO, could be obtained from water glass, NapSiO,, whichwas decationized with Amberlite LH-120 cation exchange resin.

-98-

III. RESULTS AND DISCUSSION

Figure 1,2,3 and 4 show the effects of silicates with sodium silicate andm-silicic acid on the absorption and translocation of manganese and phosphorus.In Pig. 1 and 4, it can be readily seen that those effects differ according tothe components of culture solution. The results, however, did not show anyremarkable difference between varieties, Kwanok and Jinhung, or ages of testplants, 20 and 50 days old.

There exists a considerable degree of correspondence between presentresults and other investigations (12, 13, 19, 20) on that the absorption ofmanganese and phosphorus decreased with increasing silicon concentration.However, one has to draw attention to tho following facts:

1} Physico-chemical differences between NapSiO, and HpSiO, solutionChemical interaction of silicate with Mn or P.

If there were no apparent differences on the experimental conditionsexcept chemical forms, the properties of silicate media could be only influencedby its pH. concentration of silicates and other mineral constituents. Earlier,Roller (2; reported that m-silicic acid is hydrolyzed to form o-silicio acid.It is quite probable that such o-silicic acid might be an available form ofsilicon subsequently proposed by Yoshida (13) and Whittenberger (?).

Chemical properties of Na-SiO-j and H SiO, have been believed extremelycritical: colloidal behaviour and coagulo.tion with Mn, Fe and Mg etc., alwaysanionic reaction, and commonly inorganic existence. Although bearing in mindthe behaviours of silicate in culture solution, these important properties wouldseem to have littls ecological value here, because, in this experiment, low •concentration and controlled pH were carried out before absorption.

Eaton et al (10) have recently reported that the reaction of maaganese withsilicate is dependent upon tho degree of alkalinity and that a representativevalue for irrigation water and soil solution is around 30 ppm of SiO, (imeq. per1 litre). In addition, the solubilities of several metals in the presence ofNa-SiC-j at high pH condition were shown: Cu-^Zn vMn • -"JCd-c'-'Pt--Mo <J4g-r'Ca. Althoughit is customary to express the soluble Si found in waters and soil extracts asSiOo, it is well known that between pH 2 and 9 a largo part of the silicon ispresent in solution in the form of monosilicic acid (Si(OH)., which polymerizesto form colloidal silica when Si exceeds 50-60ppm. In "the presence ofamorphous SiOp, it has been suggested by Alexander et al. (11) that increase inalkalinity results in a progressive formation of silicates, but tho solubilitiesof Si(OH), may remain unchanged (K = 10-8).

In study on the accumulation of sodium and the postulated barrier to sodiumtransport in bean plants, Jacoby (4) concluded that a low external Nad concen-tration the logarithm of Na content in the stem is inversely related to distancefrom the stem base, but with increasing of external NaCl concentration a gradualsaturation of Na in the stem tissues and leaves seems to occur and Na distributionin the plant approaches uniformity.

This evidence supporting tho existence of Na cation as a result of thesilicate application is very useful to explain present results. If we acceptthese general roles of sodium in plant tissue, it becomes considerably familiarto understand the peculiar behaviour of silicate evolved with sodium}

- 99 -

a) sodium as a main component of the osmotic pressure and tra-nslocation withtranspiration flow through vascular system in plant, b) increase in the ratio ofalkalinity to silicate, c) interaction of sodium cations with manganese orphosphorus in solution.

A) Absorption from nutrient solutionHunter (8) and others (5,6) thought that silicates applied to soils promote,

either directly or indirectly, availability of phosphorus or prevent itsfixation, similar to an anion exchange mechanism. At the same time, Okuda (17 )and Yoshida (13) convinced thg-1- solubl^ r.ilicatessBelectively absorbed by rootsprior to phosphorus absorption, is likely to convert into insoluble form, whichin turn. obstruct simultaneous absorption of phosphorus. But this conception hasnot always been clear as well as the postulation that, in plant nutrition, siliconcan perform some of the functions of phosphorus and partially substitute forphosphorus (6, 14).

In Pig. 4» it is evident that the absorption of manganese or phosphorus isdependent upon the sources of silicon in the nutrient solutions.

Halstead 2nd Barber (9) reported that availably manganese was supplied intoseedlings of crop plants mainly by diffusion mechanism in the solution. On themanganese absorption in soil-root phase, Mulder (22), Piper (23), and Wain (24)demonstrated .that changes in valence of manganese or iron, are related to 'theavailabilitia? of the elements for plant growth. Subsequently, Brown and Jones(25)* assuming these results, e.g. ion conversion of available Mn to insolubleMn or Mn . in neutral and alkaline solution, pointed out the possibilitiesof reduction of manganic oxides into manganous at the root surface before themanganese can be absorbed.

Her (18) once wrote about colloidal silicates like this:11 Colloidal silicates may vary from rather homogeneous colloidal aggregates toextremely small ultimate units of polysilicic acids and metal hydroxides toheterogeneous masses in which either the silica or the motnl hydroxides arepresent as discrete colioid.il units held together by the other component-s."

Referring to the previous study (20 ), the amount of absorbed manganese insodium silicates and phosphorus in m-silicic. acid increa-sod with the concentrationof silicon until 50 PPm and thereafter decreased.

To speak briefly, effect of sodium silicate, relative to m-silicic acid, onthe absorption of the two nutrients is more pronounced. Now, it seems quiteprobable that at the high concentrations of sodium silicates, the mobility of:manganese in the solution would be significantly influenced by the discretecolloidal units present and also by the oxidized manganic form in a strong alkalinemedium. On- the other hand, Jinhung has absorbed manganese and phosphorus muchmore than Kwanok and the translocation rate of tho two elements in 20 days oldseedlings was greater than that of 5° days old seedlings, though amounts of P and Mnabsorbed by root .-. were greater in the latter.

- 100 -

B) Translocation from root to shootTranslccation of nutrients in biological system would depend upon the

physiological functions. Effects of silicon on the crop yields and resistanceto diseases are well known. However, the physiological role of silicon hasyet to be cleared. The nature- of silicon in plant tissue, existing as aiinsolublecellulose-silica membrane in silicifiod cell or cuticle-silica layer on thesurface of leaves, makes it difficult to reveal its organic function. Added tothe problem are 1) partial substitution of silicon for phosphorus, and 2) organicrole of silicon, e.g. cationic reaction with certain organic compounds and organosilicon properties. On the contrary, Kosower (26), Kessler (3), and others haveproved that manganese and phosphorus indispensiv&ly take pnrt in the activationof various essential enzymes.

Disregarding the chemical forms of silicon source, phosphorus in Kwanok whichabsorbs much less phosphorus than Jinhung, was readily translocated in Jinhung.If the content of phosphorus in Kwanok was less than that of Jinhung, Kwanokappears less influenced than Jinhung by silicon concentration and absorbs muchmore phosphorus than Jinhung. This is contrary to our expectation. So thisresult apparently indicates that the relation of phosphorus and silicon appearsas a specific property of a crop plant.

The curves in Fig. 3 and 4 show that there is a similar tendency on trans-location of manganese and phosphorus between sampling stages, 20 days old and50 days old seedlings, under the same conditions.

To conclude, present results have an interesting bearing on 'the characteristiceffects of the different chemical forms of silicon sources, viz. alkaline compo-nents in silicon fertilizers, on the absorption and translocation of manganeseand phosphorus.

SUMMARY

Effects of silicates on the absorption and translocation of manganese andphosphorus by rice plants, 20 and 50 days old seedlings, have boen investigated.The results obtained aie summarized as follows:

1) The absorption and translocation of Mn and P dependent upon the chemicalforms of silicate sources; The effect of Nfi^SiO, being more pronounced than HpSiO^.

2) Absorption of Mn reached maximum at the Na-SiO-j concentration of 50ppm Siwhile that of P decreased considerably at the same concentration.

3) The effect of sodium silicates on the absorption of nutrients is difficultto evaluate due to the presence of alkaline sodium. One has to take into accountthe colloidal behaviour, salt concentration in transpiration flow, and distributionof sodium and silicate in plant tissues.

- 101 -

R13FEREHCES

(1) WILLIAMS, D.F. and VLAMIS, J. 1962. The effects of silicon on yield .-.ndmanganese-54 uptake and distribution in the leaves of barley plants grown,Plant Physio. 32: 404.

(2) ROLLER, P.S. and ERVIN, G. Jr. 1940, J.A.C.S. 62:468.(3) KE3SLER, E. 1957 "Research in Photosynthesis" 1st ed. Interscicnce Publ.Inc.,

N.Y.: 243:249.(4) JACOBY, B. 1963. Function of bean roots and stem in sodium retention, Plant

Physiol. 38:445-449.(5) LETTERMAN, 0., WEISSMAN, H., and SAMMET, K. 1925. Action of silica in

increasing the yield of plants. Z. Pflanzonernahr., Dung 4A; 265-315.(6) BRENCHLEY, W.E., MASKELL, E.J. and WARINGTON, K. 1927. The interrelation

between silicon and other elements in plant nutrition. Ann. Appl. Biol.14,: 45-82.

(7) WHITT3J3ERGER, R.T. 1945. Am. J. Bot., 3_2:539.(8) HUNTER, A.S. 1965. Effects of silicate on uptake of phosphorus from soil by

four crops. Soil Sc. 100(6);391-396.(9) HALSTEAD, E.H. and BARBT2R, S.A. 1968. Manganese, uptake attributed to diffusion

from soil. Soil Sc. Soc. Am. Proc. 32:540-542.(10) EATON, F.A., McLEAN, G.W., BREDALL, G.S., and DONNER, H.E. 1968. Significance

of silica in the loss of Mg from irrigation waters. Soil Sci. 165:260-280.(11) ALEXANDER, G.B., HESTON, ¥.M. and ILER, R.K. 1954. The solubility of amorphous

silica in water. J. Phys. Chem. 58:453-455.(12) OKUDA, A. and TAKAHASHI, E. 1964. The mineral nutrition of the rice plant.

(iRRl) John Hopkins Press:123.(13) YOSHTDA, S. 1965. Chemical aspects of the role of silicon in physiology of the

rice plant. Bull, of the National Institute of Agricultural Sciences series:B. No. 15_:l-58.

(14) OOKAWA, K. 1936. Physiological function of silicon in plant. Jour, of theScience of Soil and Manure. 10;445«'

(15) KAWANQ, Z. 1961. "A study on resistance for breakage of rice culm".(16) SAMOTO, K. I960. "Rice crops and protection of lodging".(17) OKUDA, A. 1958. Bull, of the National Institute of Agricultural Sciences,

48:194.(18) ILER, R.K. 1955. "The colloid chemistry of silica and silicates". Cornell

Univ. Press, N.Y., 324.(19) PARK, Y.D. 1967. The effects of silicon on rice growing, Annual Report of

O.R.D. 10:55-61.Nutrition uptake of rice in Akiochi. Ibid:23-35.

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(20) SHIM, S.C. and U, J.K. 196?. The effects of silica on the absorption ofMn-54 and P-32. Bull, of Atomic Energy Research J_:45-49.

(21) SHIM, S.C. 1968. Physical properties and chemical constituents of rice culm.Bull, of Atomic Energy Research 8/1-2):55-62.

(22) MUL2ER, E.G. and GERRSTEEN, F.C. 1952. Soil manganese in relation to pl<?ntgrowth. Advances in Agronomy IV:221-227. Academic Press, Inc. N.Y.

(23) PIPER, C.S. 1931. The availability of manganese in the soil. J. Agr. Sci.21 :762-779.

(24) WAIN, R.L., SILK, B.J. and WIELS, B.C. 1943. The fate of manganese sulfatein alkaline soils, J. Agr. Sci. 33:18-22.

(25) BROWN, J.C. and JONES, W.E. 1962. Absorption of Pe. Mn. Zn. Ca. Rb. andPhosphate ions by soybean roots that differ in their reductive capacity.Soil So. 24:173-180.

(26) KOSOWER. 1962. "Molecular Biochemistry". McGraw Hill Book Comp.Inc. N.Y.:198.

- 103 -

EVALUATION OP PYRO AND METAPHOSPHATSS AS SOURCES OP PHOSPHORUS FOR PLANTSI. UPTAKE STUDIES IN WATT3R CULTURE

A.K. Sinha and K.B. MistryBiology Division

Bhabha Atomic Research CentreTrombay, Bombay, India

ABSTRACT

Pyro and metaphosphatcs are the chief non-orthophcsphate constituents ofthe condensed or polyphosphate fertilizers which are -being developed -over recentyea'rs. While numerous tests have been carried out on the utilization of thesephosphates added to soil, little quantitative data are available .on the questionof absorption of pyro and metaphosphatc ion species by plants per se and thoextent to which utilization of these phosphates is influenced by their hydrolysisto orthophosphate forms*

The present paper reports the results of short-term water culture studieson uptake of phosphorus by maize and bean plants from ^P-labelled pyro andmetaphosphates in relation to that from orthophosphate which is the normalsource of phosphorus in plant nutrition. Concurrent measurements of hydrolysisof pyro and metaphosphates have been made.

Over uptake periods ranging from 1 to 6 days pyro and metaphosphates areslightly less efficiently utilized than the orthophosphates but the differencesare not significant. Similar results are obtained from yield data. In the veryshort treatment periods of 1 to 12 hours, however, the uptake of phosphorusfrom the pyro and metaphosphates is significantly lower than from orthophosphate.

At each uptake period, from 1 hour to 6 days, the quantity of orthophosphateformed in solution, as a result of hydrolysis of pyrophosphate, is higher thanthe total quantity of fertilizer phosphorus absorbed by plant. This is alsotrue for metaphosphate over periods of .1 day or more. The extent of hydrolysisincreases with time and is significantly enhanced in the presence of roots ofintact plants.

The markedly lower uptake of phosphorus from pyro and metaphosphates overperiods up to 12 hours can be correlated to tho relatively low orthophosphateconcentrations present in solution.

The present results suggest that phosphorus is absorbed by plants chieflyas the orthophosphate ion and the efficiency of non-orthophosphate compounds assources of phosphorus for plants growing in solution cultures is largely dependenton their conversion to orthophosphate*

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EVALUATION OF PYRO AND METAPHOSPHATES AS SOURCES OF PHOSPHORUS FOR PLANTS,I. UPTAKE STUDIES IN WATER CULTURE.

A.K. Sinha and K.B. MistryBiology Division

Bhabha Atomic Research CentreTrombay, Bombay, India

INTRODUCTION

Pyro and metaphosphatos are the chief non-orthophosphate constituents ofthe condensed or polyphosphate fertilizers which are being developed over therecent years.

A number of greenhouse and field tests of the efficiency of pyrophosphates(1,2,3,4) and metaphosphates (5,6,7,8,9,10) added to the soil have been carriedout. Recently attempts have been made to elucidate the factors affecting theconversion of pyrophosphate to orthophosphate in soil (l,2,ll) and studies madeat the Tennessee Valley Authority (TVA) have examined the chemistry of reactionof the condensed phosphates in aqueous systems and in the soil (12,13,14).

However, very little quantitative information is available on the questionwhether pyrophosphate and metaphosphate ions are absorbed by plants per se toany significant extent and on the extent to which the utilization of thesephosphates is influenced by their hydrolysis to the orthophosphate forms (l?).

It was considered worthwhile, therefore, to examine the plant uptake ofphosphorus added as pyro and metaphosphates under the controlled conditions ofwater culture. Only water-soluble compounds were selected for this study andsince orthophosphate is the normal source of phosphorus in plant nutrition itwas decided to evaluate the efficiency of the condensed phosphates in relationto that of the corresponding orthophosphates. The hydrolysis of pyro and meta-phosphates under conditions of the water culture experiments was concurrentlyexamined. This paper reports the results of relatively short-term studies onthese aspects.

EXPERIMENTAL METHODS

For the present study a number of pyro, meta and orthophosphates wereprepared in the laboratory and labelled with '^P at specific activity levelsranging from 0.3-0.5 mC./g.P. The compounds were: Potassium pyrophosphateK.PgO-, sodium pyrophosphate Na.ppO-, ammonium tetrametaphosphate NH.H PO.,pdtassium orthophosphate KHpPO. and sodium orthophosphate NaHoPO..

Sodium and potassium pyrophosphates and sodium and potassium metaphosphateswere prepared according to the methods described by Lehr et al (15). Ammoniummetaphosphate was prepared by the method supplied by TVA 1[l6T~which is essentiallythat of Thilo and Ratz (17). The orthophosphates were prepared by dissolvingthe salts in a minimum quantity of water, adding carrier-free P andrecrystallizing under a heat lamp.

Total phosphorus content in the compounds was estimated by the method ofBarton (18). The pyro and metaphosphates were hydrolyzed to orthophosphate by

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boiling with mineral acid before assay. Chemical purity of the labelled compounds,especially the condensed phosphates, was checked by the paper ohromatographicprocedure of Karl-Kroupa (19). The resulting radiochromatograms were scanned ina Nuclear Chicago Actigraph Scanner. The chemical species for each compound wasassigned on the basis of their total P.content and chromatographic data.

For water culture experiments maize (Zea mays) var. NP 65 K and red kidneybeans (Phaseolus vulgaris) var. Local were used as experimental plants. The seedswere germinated in purified quartz and when the plants were 8 days old they weretransferred to polythene culture jars containing deionised water for a 48 hourperiod. Subsequently, the plants were treated with the labelled phosphate sourcesdissolved in deionised water in culture jars containing 900 ml of the solution.Normally two plants were grown in ..each jar and five replications were maintainedfor each treatment. The quantity of phosphates added and tho periods of treatmentwhich varied in different experiments are indicated under TSxrperimental Results.The experiments were carried out in a growth room which permitted reproducible en-vironmental conditions. The temperature was maintained at 23 +_ 2 C, relativehumidity at 65 5 per cent and the plants were illuminated in 12 hour periodsat 600 footcandTes.

Since preliminary experiments in nutrient solutions indicated marked andvariable effects of the different nutrient ions on the hydrolysis of condensedphosphates it was decided to carry out the experiments in deionised water systems.The plants were observed to be healthy at the end of 6 days which was the longesttreatment period employed.

After treatment the plants were sacrificed and separated into shoots and roots.Roots were given a 10 second rinse in distilled water to remove superficiallyretained solution. The tissues were dried in an oven at 105°C, weighed and wet-ashed with concentrated nitric acid till clear extracts were obtained. Total Pin the extracts was estimated by the method of Barton (18) and 32p assayed bycounting 1.0 ml. aliquots in a G-M tube after drying under a heat lamp. Radio-chemical data were processed to compute- the plant uptake of phosphorus and percentutilization of the added phosphates.

For measurements of the hydrolysis of pyro and metaphosphates at intervals -vcorresponding to those of plant uptake identical jars containing the labelledphosphate solutions but without plants were set up. At different periods suitablealiquots were withdrawn from these jars and the quantity of orthophosphate formedwas estimated by the method of Dickman and Bray (20), which is highly specificfor orthophosphate. Parallel estimations on solutions in which plants were grownwere made to study the influence of root activity on the hydrolytic process.

EXPSRIMSNTAL RESULTS

a. Studies on pyrophosphateData on utilization of potassium pyrophosphate and potassium orthophosphate by

intact maize plants over uptake periods ranging from 1 to 6 days are presented intable I.

It is evident that while the orthophosphate is marginally more efficientlyutilized than pyrophosphato over-all treatment periods tho differences between thetwo sources are not significant except for the shoot values after 1 day. Data on

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yield of dry matter (table II) also show, in general, no significant differencebetween the growth of plants under pyro and orthophosphate treatments over theshort uptake periods employed.

Data on the hydrolysis of potassium pyrophosphate in solution are reportedin table III. It is apparent that potassium pyrophosphate undergoes hydrolysisand measurable quantities of orthophosphate were present after 1 day; the extentof hydrolysis increased with time and was enhanced in solutions in which plantswere grown.

It is of interest to note that the amount of orthophosphate P present insolution, as a result of hydrolysis of the pyrophosphate, was more than the amountof fertilizer P absorbed by plants over each treatment period.

Data on the influence of plant species on th& uptake of P from pyro and ortho-phosphates are reported in table IV. It is seen that for both phosphate sourcesthe fertilizer phosphorus uptake (computed per g. dry weight) by beans ismarkedly higher than that by maize. However, relatively greater fraction of theabsorbed P is translocated to tho shoots in maize resulting in significantlyhigher values of transport indexj this is true of both pyrophosphate and ortho-phosphate treatments.b. Studios on metaphosphate

Data on the,.comparative utilization of ammonium meta and orthophosphates bymaize are presented in table V. Data show increased utilization of metaphosphatewith time and over tho relatively short uptake periods employed accumulation ofP in roots is seen to bo considerably more than its transport to the aerialtissues. Comparison with the data on uptake of ammonium orthophosphate revealsrelatively greater utilization of the orthophosphate over each treatment period.However, the differences between the two sources are not statistically significant.

Similar effects are evident in the data on the yield of dry matter (table Vl)which indicate marginally higher yields with orthophosphate.

Data on the hydrolysis of ammonium metaphosphate at concentrations identicalto those in the uptake experiments are reported in table VII. It is seen thatsignificant quantities of orthophosphate were formed in 1 day and the extent ofhydrolysis increased with time. As in the case of pyrophosphate (Sec. a) thehydrolysis is markedly influenced by roots of intact plants and the amount oforthophosphate P formed in solution over successive treatment periods issignificantly greater than the quantity of fertilizer P absorbed by plints underconditions of our experiments.

Comparative uptake of P from ammonium meta and orthophosphates by maize andbeans is reported in table VIII. Over identical duration of growth the accumu-lation of fertilizer P by roots is greater in bean plants while its upward trans-location is higher in maize. Similar interspecific differences are observed withboth phosphate sources.c« Very short-term studies on plant uptake and hydrolysis of pyro and mctaphosphatea.

Data reported in earlier sections showed that even after 1 day, which was theshortest period of treatment in these experiments, orthophosphate was formed, asa result of hydrolysis of the pyro and metaphosphates in solution, in concentra-tions high enough to account for the uptake of P by plants growing in thesesolutions. Since these results do not permit definite conclusions on the questionwhether phosphate ions other than the orthophosphate are absorbed by plants very

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short-term studies with experimental periods ranging from 1 to 12 hours wereundertaken.

Data on uptake of P by maize plans from solutions of sodium pyro, meta andorthophcsphates after 1,3,6 and 12 hours are reported in table IX. It isobserved that over these extremely short uptake periods the absorption of Pfrom orthophosphate was significantly greater than that from the other sources.This finding is in contrast to the situation over relatively longer periods ofuptake of 1 day or more. It is seen that the difference between phosphorusuptake from orthophosphate and the other sources is greatest at the shortestperiod of uptake, i.e. 1 hour and tends to narrow over increasing treatmentperiods. Data show that the uptake of P (expressed as ug.P/jar) from sodiummetaphosphate is significantly less than that from the pyrophosphate. However,the differences between meta and pyrophosphate may, at least in part, be dueto the smaller quantity of metaphosphate added to the uptake solution. This isevident when the uptake data are recalculated as per cent utilization of thephosphates.

Concurrent measurements of hydrolysis of the condensed phosphates (table X)reveal measurable, though very low, concentrations of orthophosphate insolution. After 1 hour about 0.6 per cent of the pyrophosphate and 0.3 per centof the metaphosphate were hydrolysed. The extent of hydrolysis.increased withtime and after 12 hours per cent hydrolysis values of 5»® and 4.0 were obtainedfor the pyro and metaphosphate, respectively. It is noteworthy that the presenceof plant roots in solution appeared to enhance the rate of hydrolysis of thepyrophosphate even over very short periods.

Comparative data on hydrolysis of the condensed phosphates and plant uptakeof P from these sources over 1 to 12 hour periods are presented in table XI.It is evident that even at the extremely short uptake periods the amount oforthophosphate formed in solution as a result of the hydrolysis of sodium pyro-phosphate is greater than the quantity of fertilizer P absorbed by plants.In contrast, plant uptake of P from sodium metaphosphate is marginally higherthan the quantity of fertilizer P absorbed by plants. In contrast, plant uptakeof P from sodium metaphosphate is marginally higher than the quantity of ortho-phosphate P formed in solution at each of the four uptake periods.

DISCUSSIOH

Our findings on relative uptake of phosphorus from pyrophosphate and ortho-phosphate over very short periods are similar to the results of Sutton and Larsen(l),whp found that in waiter-culture experiments at pH 6.5 phosphorus uptake byintact barley plants from sodium orthophosphate was more than twice that fromsodium pyrophosphate over 3-J hour uptake period.

The hydrolysis data on pyrophosphates indicate that at each uptake period,from 1 hour to 6 days, the concentration of orthophosphate formed in solution ishigher than the total quantity of fertilizer phosphorus absorbed "by•plant. Thisis also true for metaphosphates over the relatively longer periods of 1 day andmore. However, the amount of orthophosphate formed in solutions of metaphos-phate in periods up to 12 hours was lower than the quantity of fertilizerphosphorus absorbed by plant over the corresponding period suggesting thepossible absorption of phosphate ion species other than orthophosphate (i.e.metaphosphate).

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The present data on hydrolysis of pyrophosphate are not in agreement withthose of Button and Larson (l), who have reported no hydrolysis of sodium pyro-phosphate (Na2BLP207) at pE 6.5 in 3-g- hours. While the pyrophosphate speciesused in our experiments (P20 ~4) and the initial pH of solution (pH 8.8) are notstrictly comparable with tnose of Sutton and Larsen, it is stressed that underour experimental conditions the.extent of hydrolysis to orthophosphate occurringover 1 to 12 hour periods could account for the phosphorus uptake by plants.

Our data indicate that the hydrolysis of pyro and metaphosphates, especiallyover longer periods, is considerably enhanced in the presence of plant roots.It has been reported that hydrolysis of pyrophosphate is influenced by pH,enzymatic activity and ionic environment in the solution (l, 11, 21). It is con-ceivable that as a result of the metabolic activity associated with roots of intactplants changes in pH and the ionic composition of the external solution can occurwhich may lead to an increased rate of hydrolysis. Activity of the microorganismsassociated with roots in the non-sterile conditions such as those prevailing inour experiments (22) are also likely to influence the conversion of pyrophosphateat least in the close proximity of the roots. While the possible influence ofthese factors on the hydrolysis of metaphosphats has not been reported it islikely that similar effects may occur.

The markedly lower uptake oi phosphorus from pyro and metaphosphaxe ascompared to that from crthophosphate over periods up to 12 hours can be correlatedto the relatively low concentrations of orthophosphate present in solutions ofthe non-orthophosphate sources at the very short treatment periods.

The present findings suggest that phosphorus is absorbed by plants chieflyas the orthophosphate ion and the efficiency of non-orthophosphate compounds assources of phosphorus for plants growing in solution cultures is 'largely dependenton their conversion to orthophosphate.

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REFERENCES

(1) STJTTON, C.D., L/.HSW, 3. Soil Sci. 9J. (1964) 196.(2) LEHR, J.R., HJGELSTAD, P.O., BROWN, E.H. Proc. Soil Sci. Soc. Amer. 28 (1964)

396.(3) SAMPLE, E.D., M.S. Thesis, University of North Carolina, Raleigh (1965).(4) SUTTON, C.D., GUNARY, D., LARSPN, S. Soil Sci. 101 (1966) 199.(5) STANFORD, G., HIGNETT, T.P. Proc. Soil and Crop Sci. Soc. Florida 1J_ (1957)

161.(6) TERMAN, G.L., DEMENT, J.D. Agron J. 4 (1962) 433.(7) HAGIN, J. Soil Sci. 102 (1966) 373.(8) DATTA, N.P., MISTRY, K.B. Proc. 2nd UN Int. Conf. PUAE 27_ (1958) 182.(9) MISTRY, K.B., IAEA/FAO Symp. Radioisotopes in Soil-Plant Nutrition Studies,

IAEA, Vienna (1962) 427.(10) SINHA, A.K., Ph. D. Thesis, Indian Agricultural Research Institute, New

Delhi (1967).(11) GILLIAM, J.W., SAMPLE, E.G., $oil Sci. 106 (1968) 352.(12) HUFFMAN, E.O., FLEMING, J.D. J. Phys. Chem. 64 (i960) 240. '(13) PHILEN, O.D., Jr. LEHR, J.R. Proc. Soil Sci. Soc. Amer. 31. (1967) 196,(14) HUFFMAN, E.O. Outlook on Agriculture £ (1968) 202.(15) LEHR, J.R. et al. Chem. Engng. Bull. No. 6, Tennessee Valley Authority (1967).(16) HIGNETT, T.P. Personal Communication.(17) THILO, E., RATZ, R. Z. Anorg. Allgem. Chem. 260 (1949) 260.(18) BARTON, G. Anal. Chem. 20 (1948) 1066(19) KARL-EROUPA, E. /nal. Chem. 28 (1956) 1091.(20) DICKMANN, S.R., BRAY, R.H. Ind. Engng. Chem. Anal. Ed. 12 (1940) 665.(21) WAZER, J.R. Van. Phosphorus and its Compounds. I. Chemistry, Interscience

Publishers, New York (1958).(22) BARBER, D.A. Ann. Rev. Plant Physiol. !£ (1968) 71.

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TABL3 I

Comparative utilization of pyro and orthophosphates by maize plants in water culture

Phosphate Initialsource pH

Potassium 8.8pyrophosphat e

Potassium 5*3orthopho sphat e

Significance ofdifference (F)

Quantity Utilization of fertilizer phosphorus ( of added)added 1 day 3 days 6 days(mg.P/jar) Shoot Root Total Shoot Root Total Shoot Root Total

plant . plant . plant20.2 0.07 0.33 0.40 0.42 1.11 1.53 1.46 1.15 2.6l

20.5 0.1? 0.60 0.75 0.55 0.99 1-54 1.14 1.75 2.89

0.05 NS NS NS NS 5S NS NS . NS

TABLT? II

Comparative.effect of pyro and orthophosphates on growth of maize plants in water culture

Phosphatesource

InitialpH

Quantityadded(mg.P/jar)

1 dayShoot Boot

Yield of dry matter (g/jar)3 days 6 daya

Shoot _ Root______Shoot____Root

Potassiumpyropho sphat e

8.8 20.2 0.132 0.090 0.174 0.113 0.213 0.133

Potassiumo rthopho spha t e 5*3 20.5 0.144 0.100 0.187 0.097 0.173 0.122

10 Significance of• difference (?) 0.05

TABLE III

Hydrolysis of pyrophosphate in water cultureQuantity added t 20.2 nig.P/jarInitial pH t 8.8

1t-*»-*u*t

Days

1

3

6

Orthophosphate(mp.P/iar}

Ko.plant1.01

1.15

1.24

in solutionaWithplant1.23

1.36

1.39

a.b.Uptake of fertilizer phosphorus by plant

(mg.P/jar)

0.08

0.33

0.53

ai) With two maize plants per jar

Total plant (shoot •«• root) value*.

ii) not corrected for fertilizer phosphorus uptakeby plants.

TABLE IVEffect of giant species on jphosphgrua uptake and translooation from py™ a«n n>.+.h»rv>ffT,ha+fr^ " ™ ™ ™ ™ ™ " ^ " ™ ™ ™ ™ ™ ™ ™ ™ " ^ " ™ ™ ™ ^ ^ " ^ " ™ ™ ™ ^ ^ ^ ^ I ™ ™ ™ ™ ™ ™ ™ ™ ^ ^ ™ ^ ^ ' ^ " ^ ^ ^ ^ ^ ^ ^ ™ ^ " ^ ^ I SE ^ ^ J* ^ ^ * ^

sources, in water cultureDuration of treatment t 6 days

Phosphatesource Fertilizer phosphorus uptake (mg/g dry wt)

Shoot RootMaize Bean Maize Bean

Transport index8Maize Bean

PotassiumPyrophosphate 1.43 1.83 1.77 7.26 45 20

,_ Potassium 1.53£ orthophosphate 2.19 3.25 7.55 32 22

transport index - Shoot, content ————Total plant content

TABLE V

Comparative utilization of meta and orthophosphates b^ maizeplants in water culture

Phosphate Initial Quantity Utilization of fertilizer phosphorus ($ of added)source pH added 1 day 3 days 6 days

(mg.P/ ar) Shoot Root Total Shoot Hoot Total Shoot Boot Total________.^sia_l_________._________________. _______Plant_____________ plant_____________ plant

Ammonium 6.6 1.86 1.32 3.40 4.72 4.86 7.34 12.20 13.76 11.60 25.36metaphosphate

i Ammonium 5.0 1.89 1.94 4.46 6.40 6.64 8.44 15.08 13.SO 11.94 25.44H- orthophosphateVJl

ISignificance of US ITS NS US ITS FS NS FS NSdifferene (?)

TABLE VIComparative effect of meta and orthophoaphates on growth of maiae^

plants in water culture

Phosphatesource

Initial QuantitypH added

(mg.P/j.ar)Yield of dry matter (g/jar)

1 day 3 days 6 daysShoot Root Shoot Root Shoot Roc.t

Ammonium 6.6metaphosphate

1.86 0.115 0.083 0.131 0.084 0.164 0.088

Ammoniumorthopho sphat e

1.89 0.145 0.089 0.156 0.092 0.150 0.099

Significance ofdifference (?) NS ira S3 TtS ns NS

TABLE VII

Hydrolysis of metaphosphate in water cultureQuantity added s 1.86 mg.P/jarInitial pH : 6.6

Days

1

3

6

Orthcphosphate in(mg.P/jar)

Noplant0.14

0.18

0.27

solution

awithplant0.22

1.20

1.26

a.b. Uptake of fertilizer phosphorus by plant(mg.P/jar)

0.09

0.23

0.47

ai) With two maize plants per jar0 Total plant (shoot and root) values.

ii) Not corrected for fertilizer phosphorus uptake by plants,

TABLg VIIISffcot of j>lant species on phoophorus uptake and translocrtti-'n frc^m

mota and[ orthnphnsphatft sources in water culiurgDuration of treatment = 6 days

Phosphatesource

Fertilizer phosphorusShoot

Maize Beanuptake (mg/g dry

RootMaize Bean

wt.) TransportMaize

indexBonn

Ammoniummetaphosphate 1.63 1.03 2.44 2.78 40 27

i Ammonium»-; orthophosphate 1.80 0.88oo 2.60 3.18 41 18

"Transport index Sh00- contentTotal plant content x 100

TA3LE IX

Phosphorus uptake from ofvro1 meta and orthophosphate by maize plants over very, short periodsin water culture

Phosphatesource

Sod iximpyrophosphatr

InitialpH

8.8

Quantityadded(mg.P/jar) 1 h

of fertilizer phosphorus (ug.P/jar)Shoots Roots

3 h 6 h 1 2 h I h 3 h 6 h 12 h

25.4 0.8 15.8 71.4 199-5 B5.9 182,7 299.7 436.0

Sodium 6.4mf>t a phosphate

^ Sod iun 5*21 orthophosphate

L.e.d. (P = 0.05)

7.0

26.4

0.2 3.2 24.3 55-1 .O 65.2 139.1 247.7

3.7 58.8 226.1 342.3 183.3 400.4 648.8 840.7

1.8 11.8 36.5 70.7 7.3 38.7 62.3 82.9

aWith two plants per jar.

TABL3 X

flydrolysis of pyro and nrntaphogphates over very short ~

Phosphate Initialsource pH

Sod iura 8*8pyrophosphate

Sodium 6.4met a phosphate

' ~" _ -

- 2£lty ,h Hydrolysis (me. orthophosphate P/jar)(mg.P/oar) No awith No aWith

——— ^— . plant plant plant Dlant

25.4 0.16 0.96 1.17

7*° °-02 0.04 0.03" -• - i * .

v** a iiin

No aWith No aWith—— Plant . ——— plant ——— lant —— plant

0.89 0.87 1.20 1.29

0.14 0.08 0.26 0.26

i) With two maize plants per jar.ii) Not corrected for fertilizer phosphorus uptake by plants.

TABLE XI

Comparative data on hydrolysis of pyro and metnjshoaphates and plantuptakf__of phosphorus'from these sources over short 'treatment

periods

Phosphate Initial Quantity Hydrolysis bUptake of fertilizer phosphorus by plantsource pH added (mg orthophosphate P/jar) (mg.P/jar)

(mg.P/jar) 1 h 3 h 6 h 12 h 1 h 3 h 6 h 12 h

Sod iumpyrophosphate 8.8 25.4 0.1* 0.96 0.89 1*20 0.09 0.20 0.3? 0.64

Sod iumg metaphosphate 6.4 7.0 0.02 0.04 6.14 0.26 0.03 0.07 0.16 0.30l

Sodiumorthophosphat? 5.2 26.4 26.4 26.4 26.4 26.4 0.19 0.46 0.87 1.18

In absence of plantsTotal plant (shoot + root) values with two maize plants per jar.

EEPORT ON THE USE OP RADIOISOTOPB'.' 32P FOR FERTILIZERSTUDIES IN INDONESIA

Nazir Abdullah

The application of radioisotopes in agricultural research, in Indonesiahas been limited by the existing facilities and urgency of the problems faced.Up till now only a few works had been conducted using radioisotope 32p forfertilizer studies.

Experiments on the technique of phosphate fertilizer placement werecarried out with rice at Pasar Djumat Research Centre of the National AtomicEnergy Agency, while work on maize was done at Bogor Institute of 'AgriculturalSciences.

From the data collected, it appears that with respect to placement on rice,broadcast was the best method for the uptake of phosphorus, while mixing a partof phosphate fertilizer to the maize seeds, resulted in better growth at earlystage of development. Mixing the fertilizer with seeds was especially recommen-ded for small seeded maize.

32An experiment was also carried out using P to study the effect of ferti-lizer and liming in field conditions for areas planted with kidney beans(Phaseolus lunatus L.). Results from this experimental work showed that thissoil gave a great response to the NPK fertilization. Liming the soil with adose of 4 - 6 tons of lime per hectare increased the efficiency of NPK fertili-zation. This efficiency might be partly due to the increase of phosphorusavailability for the plants and by the decrease of P fixation by the soil.

Some other experiments are still going on at Pasar Djumat Research Centreon the use of radio£hb.sphorus for fertilizer studies in rice.

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REPORT ON THE USE OP RADIOISOTOPE 32P FOR.FERTILIZERSTUDIES IN INDONESIA

4t^f \Nazir Abdullah 'Pasar Djumat Research Centre

The National Atomic Energy Agency Djakarta, Indonesia

1. INTRODUCTION

The application of radioisotopes in agricultural research in Indonesia hasbeen limited by the existing facilities and urgency of the problems faced. Radio-isotope technique is not widely used yet in agricultural research in Indonesia.Research on the use of radiophosphorus in the tracer technique has been initiatedjust after the Triga Mark Reactor at Bandung started to produce several kinds ofradioisotopes (10). Up till the present QQly few experimental work has been donein the field of fertilizer studies using P.

Lack of research workers who are familiar with this new technique and alsolack of certain electronic equipment in several agricultural research institutesare the main handicap which explains why the radioisotope techniques have beendeveloped slowly. However, this does not mean that the use of radioisotopes inseveral fields of agricultural studies are unacceptable by the research workers.Some activities had been carried out by the very limited well trained staff atPasar Djumat Research Centre. In addition, a few experimental works had beenundertaken in co-operation with the staff of the Bogor Institute of AgriculturalSciences at Bogor.

Other problems faced by the research workers in the past was the unregularityof the radioisotope production and the limited quantity which is available.Although these problems caused a discontinuity of "the experimental work in thepast, we always believe that the intensity of work in this new field of studywill be increased in the coming years.

The purpose of this paper is to summarize the results obtained from researchdone in Indonesia concerning the USB of radioiaotope *^p in fertilizer experiments.

*) A paper presented on the Asia and the Far East Study Group Meeting on the Useof Isotopes and Radiation in Investigations of Fertilizer and Water UseEfficiency, held in Bangkok, Thailand, 21-25 April 1969. Contribution of theNational Atomic Energy Agency, Djakarta, Indonesia.

**) Technical Staff Member at Pasar Djumat Research Centre of National AtomicEnergy Agency, Djakarta, Indonesia.

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2. EXPERIMENTAL WORKS AT PASAR DJUMAT RESEARCH CENTRE

WIDJANG al_. (13) studied the uptake of phosphorus in rice for threedifferent methods of fertilizer application, namely (i) surface broadcast, (ii)band application, 5 cm from the seeds and 7 cm below the seeds and (iii) mixedwith the soil. Phosphorus (Po c) was applied in the form of Double Superphosphateat the rate of 100 kg per hectare (38 per cent P2°5^* In addition 10° k& ofUrea (45 per cent N) was also applied.

The experiment was conducted in pots containing 2 kg of soil. The amountof fertilizer used per pot was 100 rag each of Double Superphosphate and Urea.Twenty seeds of "Sigadis11 rice variety were planted in two rows for each pot.

The plants were harvested at an interval of 14, 28, 42 and 56 days from thedate of planting. Fifteen plants were harvested at the first interval. Forsucceeding intervals the number of plants harvested were 5» 2 and 2 per potrespectively. The determination of the P uptake by the plants, derived fromfertilizer was done by means of a comparison between the specific activity ofP in the plants and the specific activity of •* P applied to the soil. Phospho-

rus uptake from fertilizer was determined by bioassays.Table I showed that not all the treatments with surface broadcast gave the

highest quantity of dry matter and it should also be mentioned that the highestquantity of dry matter does not always yield the highest phosphorus content inthe plant.

TABLE I. AVERAGE DRY MATTER YIELD AND PHOSPHORUS CONTEST OF THE PLANT

Ages of the plantsTREATMENT

D.M.14

P.C.28

D.M. P.C.42

D.M. P.C. D.M56

P .C.

ControlBroadcastBandMixed

400.5388,

'.5 - 743. y - 1200.0 - 1J5B.O..0 2.85xlO~4 755.9 6.00xlO"4103l.4 1.65xlO~3 1438.9 1.17xlO~3

__.0 6.15xlO~6 846.0 8.25xlO~4ll02.3 1.35xlO~3 1395.0 l.60xlO~3358.5 4.35xlO~5 610.6 3.05xlO~4 897.0 0.69xlO~3 1219.5 0.88xlO~3

Legcnda: D.M.P.C.

dry matter (mg)phosphorus content (mg)

The results obtained from different methods of phosphate fertilizer placementin this experimental work were as followsj

(i) The highest uptake of phosphorus by rice plants harvested 14 days afterplanting was derived from surface broadcast and followed by mixed treatment.This might be taken into .consideration, that during this period of growthphosphorus was not well spread yet into the soil.

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(ii) The plants harvested 28 days after planting showed that the highest,phosphorus uptake obtained was by-hand treatm-ent, followed by surface broadcast.It might be understood that during this period of growth phosphorus moved alreadyvertical into the soil and spread to the top-layer of the soil and reached the roottopis; - • ••••• - ••" • • - - • • • • - - • • • - • • • • ...........

-•(iii-) The plants harvested 42 arid -56-days-aflrer planting gave the highest Puptake-by "surface broadcast-and band treatment-respectively. • "The" 'lower"P fixingcapacity may explain the higher P uptake in band treatment.

This experiment Was conducted under supervision of an IAEA, expert who hadbeen employed at Pasar Djumat Research.Centre for several months in 1968. Due toinsufficient suppl-y -of radioisotope ^2p received -from Bandung Reactor, this "experimental work was conducted only with two replications. It might be consideredas a preliminary investigation for the basic experiences of this new technique forfuture works. !

Another experiment was_carried out in 1966 (8) with a rather .different .,technique 'in the methods of placement and the forms of fertilizer used. A potexperiment was conducted to study the different methods of placement of phosphatefertilizer by means of.labelling with 2P. Plastic pots with a diameter of 28 cmfilled with 7 kg of top soil, from Pasar Djumat Experimental Garden and a basic doseof fertilizer applied at a rate of 100 kg per. hec.tare Potassium Sulphate--andAmmonium "Sulphate, equal to 200 mg each fertilizer per pot. Labelled NaH^ PO.was used as labelled fertilizer. Seven rice seeds of "Bengawan" variety plantedin each pot with a distance of 9 x 9 cm. Five different methods of placement withfour replications were as follows:

*' Control," without" phosphate fertilizerPlacement on surface broadcastPlacement at a depth of 3 cm from the surface directly below the seedPlacement at a depth of 3 cm from the surface and 3 cm below the seedPlacement at a depth of 3 cm from the surface and 6 cm below the seed.Placement just above the seed and under the 'surface

The plants were harvested at 14, 28 and 42 days after planting. The charactersstudied were plant height, fresh weight, dry weight, counting yield and percentageP uptake. The surface broadcast gave the highest result for all the charactersstudied for all ages except for plant height at 42 days after planting (table II).It should be noted that there is a positive relationship between dry weight as wellas percentage P uptake with the ages of plants harvested. In case of dry matteryield obtained from this experiment the results confirm KHAN's Ua . report (?),that in all participating countries of the PAO/IAEA Co-ordinated Research Programme,the highest dry matter yield was obtained from surface treatment, except inPakistan.

- 125 -

TABLE II. THE EFFECTS OF FERTILIZER PLAC -MENT ON PLANT HEIGHT, FRESH WEIGHT,DRY WEIGHT, COUNTING YIELD AND PERCENTAGE OF P UPTAKE IN RICE

CSARACT.STUDIESPLANTHEIGHT(cm)

FRESHWEIGHT(mg)

DRYWEIGHT

COUNTINGYIELD(cpm)

HUPTAKE

( # )

AGES OFPLANT(S) A

142842

142842

142842

142842

142842

33.672.2

106.0

164.33,0419,866

29.1515.5

3,119

---

--

B36,76,

104,

-1• 5.5

218.03,889

16,227

38.646.

4,005

9,61626,46615,753

•'' 0.0.

7.

211

86

2

91513

07672250

TREATMENTC

34.969.1

110.0

164.5,651 3,450 10

25.6461.1

,829 2

,498 4,500. 6,359 8

D3271

108

197,240,922

^^^^^^^H

34540

,931

,170,550,491

.8

.3

.5

.326

.3

.42

10

4

fr.075 0.0330.4236.35

0.1794.04

IS

3167

105

177,747,747

30499

,211

538,800,405

.4

.6

.2

.725

.5

.6

F

316793

153,781,424

26550

REMARKS

.3

.9

.3

.0

.8

.62,572

92310

0.005C.2672.48

,491,692,066

0.0750.6465.28

Legenda: A : Control,without phosphate fertilizerB : Placement on surface "broadcastCt: Placement at a depth of 3 cm from the surface and directly

below the seedD : Placement at a depth of 3 cm from the surface and 3 cm

below the seedE s Placement at a depth of 3 cm from the surface and 6 cm

below the seedF : Placement just above the seed and under the surface

- 126 -

3. ACTIVITIES IN CO-OPTSRATION WITH OTHER INSTITUTES

Fertilizer studies on maize plant was done in co-operation with the staffof the Bogor Institute of Agricultural Sciences at Bogor (9). To minimize theP fixation "by soil components, phosphate fertilizer can bo placed localized toprevent more contact with the soil. Such method was recommended for solublephosphate fertilizer on maize plant grown on acidic soils (4). In this casefertilizer was placed at a distance of 7*5 cm side way the seed and 5 cm below.It has been mentioned in the literature that placing a part of phosphate ferti-lizer together with maize seeds, will stimulate the growth of young plants (5)and the yield will also be increased.

The study was intended to compare the effect of several methods of placementof ^P labelled Double Superphosphate on growth and uptake of phosphorus byplants. Pot experiment was carried out in greenhouse using 3 kg of "Tjidjantung"soil with a pH 6.G and P fixing capacity was about 94$ (14). Each pot wasplanted with 10 seeds and harvesting took place at the ages of 11, 16, 22 and 27days after planting. Bioassays were made according to the methods used byG'O BAN HONG (l) and the activity measured with G.M. Counter. The resultsobtained in this experiment are presented in table Ilia.

The results indicate that the dry weight was affected by fertilizer placement,(9). Randomized block design was used with three replications. Two soilsamples were used in this experiment, the Botanic Garden's Latosol (BGL) richwith nutrient and another soil sample Tjibinong Latosol (TBL) poor with nutrient.The pH values were 6.2 and 5.0 respectively. The results obtained in thisexperiment - are .shown in tabl& Illb. 'TABLE Ilia. AVERAGE DRY MATTER (mg/ 2 plants) AND MEAN PLANT ACTIVITY (counts/

min/ 2 plants) AS AFFECTED BY DOSIS AND PLACEMENT OF PHOSPHATE...... - FERTILIZER . . . . . .

TREATMENT

A.B.C.D.E.F.

e.p.i.p- i1 hilll.P-2 hills2.P-2 hills

D.W.

247231272258

l.P-Mixed 2431/3 P-

. mixed .2/3 P-1 hill

240

11C.

-a

19151754

. t

Ages of16

D.W. C.

579585537546642690

-15333219;33

plants2:

D.W.

1321165212251452

i. 1213: 1728

?C.

-13413398684

D.W.

213226852635241022252745

.

27C.

-14949358246322

Spec,activ.at27 'dCDm/nu?

00000

-.06 '.19.24 -'.02.12

r '

Legenda : D.W. : dry weight (mg)C. : counting (counts/min.)

32l.P i 1 g Double Superphosphate per pot plus 1 uc P. Each pot contained3 kg "Tjidjantung" soil introduced with Nitrogen (l g Urea) and Potassiumoxide (l g Potassium Sulphate) Fertilizer and planted with 10 maize seeds of"Harapan" variety.

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The data indicated that the Botanic Garden's soil gave better growth andthe P uptake was higher than that derived from Tjibinong's soil. Furthermoresmall seeded maize gave the;. highest P uptake for both types of soil. By mixinga part of fertilizer with the seeds, the P uptake was increased. The resultsmentioned above indicated that for small seeded maize, mixing a part of phosphatefertilizer with the seeds was recommended since; it would increase the efficiencyof P uptake by the plants.

32An experiment was also conducted using P to study the effect of fertilizerand liming in field conditions by using kidney beans (Phasoolus lunatus L.) andthe effect of liming on the availability of phosphorus and P fixation by the soil(3). This investigation was based on the results obtained in a field experimentdone at "Panumbangan" Sukabumi, using NPK fertilizers and liming. The main plotswere treated with NPK fertilizers and without any fertilizer, while tbo sub plotsconsisted of 5 levels of liming namely 0,2,4,6,8 and 10 tons of lime per hectare.Results obtained in this experiment showed that fertilization with NPK fertilizersand liming at the rate of 4 - 6 tons per ha increased the yield up to 1 ton dryseeds per hectare. Liming alone was not much effective (table IV). The determi-nation of available phosphorus was done by extraction method according toSTANFORD & DE MEWT (ll). P fixation was determined according to SUWADJI et al.(U).TABLE Illb. THE EFFECT OF SOIL SAMPLE, SIZE OF MAIZE SEEDS, METHODS OF FERTILIZER

PLACEMENT ON DRY MATTER (mg/pot) ART UPTAKE OF 32p BY SEEDLINGS AT12 DAYS OLD

TREATMENT

A.B.

C.D.

E.F.

a.H.

J.

O.P- large seed - BGL1/3

l.P1/3l.P1/3l.P1/3l.P

P-

inP-

inP-

inP-

in

with seod- 2/3P in 1large seed - BGL

hill

1 hill- large seod- BGLwith seed- 2/3 P in 1sipall seed - BGL

hill

1 hill- small seed- BGLwith seed- 2/3 P in 1large seed - TBL1 hill- largo seed -with seed- 2/3 P in 1small seed - TBL1 hill- small seed -

hill

TBLhill

TBL

Plantweight(rag)423.0390.0

416.0

383.0313.0

273.0226.0

190.0170.0

Legenda: BGL : Botanic Garden's Latosol,TBL : Tjibinong's Latosol, poorl.P : 1 g Double Superphosphate

Plantactivity(cpm)-88.

50.

312.125.

38.38.300.63.

0

0

00

00

00

P2°5

0

0

00

00

00

rich in nutrient,in nutrient, pH 5per pot plus 6 uc

-.18

.10

.65

.26

.08

.08

.64

.13pH 6.2•§2p

P2°5w-0

0

00

0C

0C

.05

.02

.17

.08

.03

.03

.34

.08

"Harapan" variety : late maturity, large seeded maize"Pendjalinan" variety, early maturity, small seeded maize

- 128 -

Table IV, THE EFFECT QF LIMING AND NPK FERTILIZERS ON SEED YIELD AND THEINFLUENCE OF LIMING ON .pH, PHOSPHORUS AVAILABILITY AND P FIXATIONIN PHASEOLPS LUNATUS L.

TfiEATMENT Field experimentLime, (tons/ha) Yield- • -

Soil analysis by means of tracertechnique (NPK & Lime Fertilization)pH (H O) Activity P fixation

(cpm)024 .6810

Mean

L*S.D. 0.05

3.43.64.94.84.5 .4.1 '

4.1: . for mean

12.910.414.817.512.012.9

13.4main pla

4.85.26.16.97.87.8

its j 1.3

835384533

. 2?

8475 .68697281

.

for mean sub pints » 4.1for sub plot in the same main plot : 5.9

The samples used for measurement were made in forms of briquets according -tothe method done by MacKMZIE jst.al. (6).

The availability of phosphorus by means of liming was closely related to Pfixation by the soil. From the data collected on table IV, it is seen that P "fixation decreased when liming was increased up to 4 - 6 tons por hectare andthe fixation was increased again as lime application was increased.*) This is inagreement to general opinion that in soil of low PH, phosphorus was also lackingdue to fixation by iron and aluminum (12). The data showed that liming withmore than 6 tons per hectare for "Panumbangan11 soil may not be recommended.

4. DISCUSSION

ATI ?lly feW exPerimontal works using 32P for fertilizer studies were undei-taken.All the results obtained in these experiments might bo classified as preliminarystudies. More research, especially on rice using radiophosphorus to study 'thefertilizer efficiency should be -done in the coming year.

*) This result is in agreement with the result obtained from maize experimenton acidic soil fertilized with lime and phosphate fertilizer.

- 129 -

Although results obtained from all those experiments were not very success-ful, a bright future and a clear direction of the beneficial effect of this newtechnique of fertilizer studies however, has come into being. Co-ordinatedresearch programmes should be conducted in the future in co-operation withseveral staffs of agricultural research institutes elsewhere in Indonesia. Themain difficulties faced in the past should be overcome soon with the new capacityof radioisotope production. The possibility of getting several kinds of radio-isotopes from the neighbour countries will stimulate the intensity of researchin Indonesia.

5. SUMMARY

A few experimental works using radioisotopes for fertilizer studies hadbeen carried out in Indonesia since 1966• Eadiophosphorus had been introducedto rice plants conducted at Pasar Djumat Research Centre of the NaUonal AtomicClergy Agency by very limited well trained staff. These activities were stilla preliminary investigation. Results showed that surface broadcast gave thehighest uptake of phosphorus by rice plants at early stage of growth, either inthe experiment carried out by WIDJANG .et al. (13) and NAZIR ABDULLAH (8).

Other activities in this field with other crops are the experiment withmaize that had been carried out in-co-operation with the Bogor Institute of Agri-cultural Sciences ($). An investigation with maize seeds to study the effect ofseed sizes and the different methods of .phosphate fertilizer placement was alsocarried out. The results obtained showed that mixing a part of phosphate ferti-lizer to the seeds caused bettor growth at young plants and increased in phosphateuptake. Mixing fertilizer with seeds was recommended especially for small seededmaize.

In relation to soil fertility improvement, an investigation was also carriedout on acidic soil, with poor nutrients by fertilization and liming on reddishbrown latosol at "Panumbangan11 using kidney beans (Phaseolus lunatus L.) asindicator (3). Results from this experimental work showed that this soil gave agreat response to NPK fertilization. Liming the soil with a dose of 4 - 6 tonsof lime per hectare may increase the efficiency of NPK fertilization. Thisefficiency might be partly due to the increase of phosphorus availability forthe plants and by the decrease of phosphorus fixation by the soil.

ACKNOWLEDGEMTJNTThe author wishes to express his profound gratitude to Prof.Dr. G.A. Siwabessy,

the Director General of the Indonesian National Atomic Energy Agency for allowingthe author to attend the meeting and to Prof.Dr. A. Amiruddin, the Director ofPasar Djumat Research Centre, for his advice in writing this manuscript and toDr. Rusli Hakim M.Sc., of the Central Institutes of Agricultural Research atBogor, for reviewing the manuscript and lastly to all staff members of the Agri-culture Division of Pasar Djumat Research Centre who in a way contributed in therealization of the experiments.

- 130 -

6. REFER 13ICES

(1) GO BAN HONG, Penjelidikan tentang neratja hara mineral padi sawah, Thesis,Bogor (1956).

(2) KANG BIAUW TJWAN, Pengapuran tanah mineral masam untuk pertanaman djagungsuatu keharusankah? bulletin Agronorai, Pakultas Pertanian Bogor 4. (1964)13.

(3) KANG BIAUW TJW/N dan NAZIR ABDULLAH, Pengaruh pemupukan NPK dan pengapuranpada Latosol merah tjoklat dari Panumbangan terhadap hasil tanaman katjangmerah (Phaseolus lunatus L.), Simposium Radioisotop 1-2 Agustus 1966 diBandung (1966). .

(4) KANG BIAUW TJWAN dan SUHJATNA EFFEtfDI, Tanaman djagung dan bortjotjok tanamdjagung varietas unggul, LKPM Kept. PTIP, Djakarta (1966).

(5) KANG BIAUW TJWAN, SUGIANTO dan SURJATNA EFFENDI, Perbedaan chasiat DS danPMP serta tjara pemupukannja terhadap pertumbuhan dan hasil pertanamandjagung (Zea Mays L.) (sedang

32(6) MacKENZIE, A.J. and DEAN, I. A., Measurement of P in Plant Material by theUse of Briquets, Anal.Chem. 22 (1950 ) 489.,

(7) KHAN, A.B., HAQ, M.S., RAHMAN, L. , HABIBULLAH, A.K.M., HABIBUL ISLAM, A.H.M.Application of Isotopes and Radiation in Rice Cultivation, PAO/IASA-AABCCo-ordinated Programme, Nucl.Sci. and Appl. Vol. II, I_, A UC Dacca (1966) 1.

(8) NAZIR ABDULLAH, Mempeladjari pengaruh ponempatan pupuk fosfat jang ditandaidengan P-3.2pada padi Bengawan (1967) unpublished.

(9) NAZIR ABDULLAH dan KANG BIAUW TJWAN, Pengaruh penempatan pupuk terhadappertumbuhan dan pengambilan fosfat oleh tanaman djagung, Simposium Radio-'isotop 1-2 Agustus 1966 di Bandung (1966).

(10) SIWABESSY, G.A. and NAZIR ABDULLAH, Radioisotopes in Agricultural Research inIndonesia. Presented on the llth Pacific Science Congress held in Tokyoon 24 August (1966).

(11 ) STANFORD, G. and DT5 MINT, J.D., A Method for Measuring Short Term NutrientAbsorption by Plants. I. Phosphor. Proc. Soil Sci. Soc. Amer. 23 (1957)355. ~~

(12) TRUOG, E., Mineral Nutrition of Plants, Univ. of Wisconsin Press (1951) 41.(13) WIDJANG, H.S., SUWADJI, "3. et_. al . , Pengaruh tjara penempatan pupuk terhadap

pengambilan unsur P oleh tanaman padi, Laporan Penelitian, Pusat PenelitianPasar Djtunat (1968 ) (unpublished. ) • •

(14) SUWADJI, E. dan KANG BIAUW TJWAN, Piksasi fosfat beberapa djenis tanah diIndonesia, Simposium Radioisotop 1-2 Agustus 1966 'di Bandung (1966).

- 131 -

THE SIGNIFICANCE OP THE 'A' VALUE CONCEPTIN FIELD FERTILIZER STUDIES1

2D.A. Rennie

ABSTRACTThis paper considers the 'A' value concept, and its application to field

experiments using labelled nitrogen and phosphorus carriers. Extensive referenceis made to phosphorus experiments carried out in Saskatchewan, Canada, and theJoint FAO/IAEA's international field research programmes on rice and wheat,using N-15 labelled carriers.

Arguments are presented which support the conclusion that'A1 value data orcalculations based thereon are not only of significance in evaluating thefertility status of soils, but also in assessing, in quantitative terms, factorsthat interact strongly with 'plant available phosphorus or nitrogen1, such asfertilizer management practices and soil moisture.

Presented to the Study Group Meeting on the Use of Isotopes and Radiation inInvestigations of Fertilizer and Water Use Efficiency, Bangkok, Thailand,21-25 April, 1969.

Q

Head, Soils, Irrigation and Crop Production Section, Joint FAO/IAEA Divisionof Atomic Energy in Agriculture, Vienna, Austria.

- 132 -

THE SIGNIFICANCE OP THE 'A' VALUE CONCEPTIN FIELD FERTILIZER STUDIES

D.A. Hennie

The 'A1 value concept (2,3) is based on the asaumption that when two sourcesof a given nutrient are present in a soil, a plant will absorb from each in pro-portion to the respective quantities available. Thus, if one source is thenative soil phosphorus and the other'an added source (fertilizer) it is onlynecessary to measure the respective quantities absorbed from each, together withthe amount of added nutrient, to calculate a value-for the native nutrient. Thislatter value, in units of the applied fertilizer nutrient is the 'A1 value.

The concept does not include the method of measurement - this is dictatedby the specific objective of the experiment (4,5,6,8,9,10,11,12,13,14), a majoradvantage of the 'A' value is that, as a quantitative measure, it' can-be-addedand subtraced and provides a measurement wherein the biologically availablenutrient status of soils, or fertilizers, can be expressed in quantitative termsrather than as a relative index. Since the rA' value is a measure of availablesoil nutrients, in units of a fertilizer standard, when the standard is changedthe magnitude of the SA' value will change. This change in the standard can bebrought about with an actual change in the fertilizer material itself, or in theposition that the fertilizer is placed with respect to the plant roots, etc.

The significance of the 'A1 value concept has not gone unchallenged. Perhapsunfortunately, however, many of those who have been critical of 'A' values haveto a large-extent misunderstood the original concept. Russell et al. (ll)presented experimental evidence which indicated that irreversable isotopicexchange may be considerable; Terman and Khasawneh (13) concluded that since inmany instances 'A' values are not constant with increasing rates of applicationof fertilizer P, that the "A1 value data are open to question.

There is little doubt but that 'mixed placement' of a tagged phosphatefertilizer standard in certain soils will be accompanied by.either, or bothsignificant isotopic exchange, and reversion of the fertilizer P standard to aless available form, thus resulting in 'A1 value data that is difficult to inter-pret in the usual manner. If irreversible exchange of P-32 occurs, or if thefertilizer standard, or a portion of it, is transformed into a less availableform in the soilj »A' values will not reaain constant as the rate of applicationis increased. However, such phenomena du not invalidate the 'A' value concept,but rather, can be taken as yet a further application, i.e. the irregularbehaviour of calculated 'A? values serves as an index of isotopic exchange, orfixation of the fertilizer standard, as the case may be.Phosphorus 'A' values using band (or seed) placement

!

Limited soil-fertilizer contact afforded by band placement of a phosphatefertilizer standard will minimize isotopic exchange and fertilizer P-fi-xation,thereby not only allowing the usual 'A1 value interpretation but -at- the sametime providing a measure, in comparison to mixed placement, of the significanceor degree of fertilizer-P fixation etc. (ll) (Table l).

In an experiment designed to measure the significance of decaying organicresidues (wheat straw) on soil phosphorus availability both banded and mixedfertilizer-P placements were used., In the presence of decaying organic residues,the mixed placement resulted in an increased in the measured 'A' value as

- 133 -

compared to the no-straw treatment; also, as the rate of fertilizer-P wasincreased, a sharp increase occurred in calculated 'A' values (Table 2). Incontrast, when the fertilizer-P was banded with the seed, a lower '41 value,relative to the control, and constant 'Af values with increasing rates offertilizer-P application were recorded. Thus mixed placement suggested that anincrease in available soil-P had occurred in the presence of decaying residues,while data from the band placement indicated the reverse. The latter was shownto be correct. However, it is important to note that the data obtained from the'mixedt placement1 does not invalidate the 'A1 value concept, but demonstratedthat the fertilizer standard was more subject to biological fixation than theavailable soil phosphorus. In 'A1 value experiments, as in most research, theinvestigator must adjust experimental procedures in accordance with the dictatesof the particular conditions encountered.Significance of Phosphorus - 'A' values

Various factors affecting the significance and usefulness of 'A1 values inmeasuring phosphorus offeets(using a band placement) are documented in thefollowing examples. Intensive data (6, 14) obtained from both field and green-house experiments have shown that in general placement of the tagged phosphorusstandard with the seed results in an uptake pattern of soil and fertilizerphosphorus such that the 'A1 value remains constant for specific soil and growingconditions (Table 3).

The 'A' value, using band placement of the phosphate fertilizer affords ameasure of the available soil phosphorus within the rooting zone (11, 14). There-fore, under field conditions, where precipitation often varies widely, 'A' valuescan be expected to vary in accordance. This is illustrated in the data given inTable 4» obtained from field experiments carried out in alternate years on thesame field sites (9). The uniformity of the NapCO^ extractable phosphorus affordsa sharp contrast to the 'A' value data. The latter were consistently low underdrought conditions, and high where favourable moisture conditions prevailed, whilethe former were constant. The 'A1 value data suggest that the biologicallyavailable soil phosphorus is low under dry conditions, and, in comparison, highduring wet years. This observation is supported by the percent yield values.

The relationship between 'A1 values and soil moisture stress is furtherillustrated in the data given in Table 5 (14). Such data provide a quantitativeestimate of the significance of a soil moisture stress on plant-available soilphosphorus. Similarly, the significance of other soil or environmental factorsaffecting root distribution can bo estimated using the 'A1 value technique (9, 14).

Terman and Khasawneh (15) questioned the significance of 'A' values since,in many instances, the values increased as the rate of P fertilization wasincreased. The data in figure 1 were obtained from field experiment where anitrogen deficiency in the soil induced, indirectly, a sharp increase in 'A1values (14), as the rate of P application was increased from 12 to 96 Ib P_0,-/ac;constant 'A1 values occurred only where the W deficiency was overcome. Ingeneral, where 'A1 values do not react in tho normal manner, the 'A' valueconcept is not invalidated, but rather there usually is a scientific explanationfor such behaviour.

- 134 -

The "Effective Hate of Application" of different P-fertilizera ' •Many workers (4,6,7,10,13,14) have assessed the availability of various

phosphorus fertilizers using «A« value data. Where an experiment is laid downon one soil, the availability of the soil phosphorus can be considered constant,and any change in the availability of the fertilizer results in a change in thesoil-P/fertiliaer-P ratio such that lower fertilizer-P uptake is reflected in ahigher 'A' value and vice versa.

Some ambiguities arise whore 'A1 values calculated in the usual manner are'compared directly since the- units change as the fertilizer standard changes.In order to avoid this difficulty, the mean comparative availabilities of thevarious fertilizers given in Table 6 are expressed as "Effective Rate ofApplication" (E.R.A.) in units of liE.E^O^, and as "Relative efficiency" in %units.The P-fertility status of soils

The significance of the 'A1 value concept (using band placement) as a meansof assessing the phosphorus fertility sta'tus of soils is further illustrated indata reported by Rennie and Clayton (8, 9). The experiments were carried outboth in the field and in the growth chamber on four genetic soil types, theCalcareous, Orthic, Illuviated and Humic .Illuviated Gleysol. These four profilesrepresent a catenary sequence that dominates the chernozemic soil area inWestern Canada. The 'A1 value data obtained from this six-year study not onlywas of significance in evaluating the relative phosphorus fertility level of thefour profiles in question but also provided data of value in assessing theeffect of various growth factors that interact strongly with soil phosphorus,such as moisture, temperature and soil structure.Nitrogen 'A1 values

The use of N-15 enables a direct measure of the fate of fertilizer N appliedto soils, particularly insofar as that portion used by plants and as in thephosphate studies reviewed above, the 'A1 value concept has similar and possiblymore significant applications.

The determination of soil nitrogen 'A1 values has b''en carried out on 12widely differing soils by Legg 3nd Stan^orf (5). They concluded that from theresults obtained there was no doubt that the 'A1 value constitutes a precisestandard for characterizing the nitrogen supplying capacity of soils. Dataselected from their study is given in Table 7. No evidence was found that themineralization rate of soil nitrogen was influenced by the addition of fertilizernitrogen; 'A1 values remained remarkably constant with increasing rate ofapplication.The Joint FAQ/IAEA's Ricd Fertility Programme

Similar data has been obtained from the Joint PAD/IAEA co-ordinated programmeon rice. Results of a greenhouse experiment conducted in the IAEA's Seibersdorflaboratory (table 8) also verify that the rate of fertilizer N application has notinfluenced the rate of mineralization of soil N (l). An ammonium sulfate sourceof nitrogen was used in these experiments in comparison to a- nitrate source inLegg and Stanford's investigations. . .

- 135 -

The 'A' value data reported in Table 9 was obtained from field experimentswith rice carried out by co-operators in the co-ordinated rice experiments. Inthese experiments the nitrogen carrier was applied as a surface dressing and ina band application at a depth cf 5 cm» At most of the locations significantlylower 'A1 values were obtained from the depth placement. The type of possiblemathematical manipulations using 'A' value data is illustrated in the columntitled E.R.A. (Effective Rate of Application). Assuming that tho depth placementresulted in the more valid estimate of available soil-N, then it can be calculated(see Table 10) that the effective rate of application of the surface placementwas 89 kg N/ha for the U.A.R. II experiment, rather than the actual 120 kg/ha.As far as can be ascertained on the basis of supporting research information (l),the difference between the actual rate of application, and the calculated T5.R./.reflects loss of fertilizer IT, primarily due to denitrification.

Usi g a similar approach, the effective rate of application in kg/ha ofselected nitrogen carriers compared to an ammonium sulfate standard effectivelyillustrates tho superiority of the ammonium sources of nitrogen as compared tonitrate sources (Table 11).The Joint FAO/IAEA's Wheat Fertility Programme

The International Wheat Fertilizer Research Programme, initiated in 1968,includes 12 participating countries. Initial data, obtained from Brazil affordsa further illustration of the significance of the 'A' value concept to nitrogenfertility studies carried out under field conditions.

The 'A' values, given in Table 12 for the* different treatments, fluctuatewidely, and in themselves, are not too meaningful. The calculated E.R.A., inunits of (NH.)2SO. (based on the 120 kg N/ha treatment), however, provides adirect, and quantitative means of evaluating 'times of application1, and relativeavailability of the two carriers used, NaNO, and (NH.)?SO..

Comparison of the 40-40-40 sequence for both carriers show that for the soiland environmental conditions prevailing within the plot site, nitrogen appliedat the early tillering stage was used most effectively, while that applied atthe boot stage was not used to any extent by the wheat.

The reasons for the superiority cf NaNO, vs (NH,.)pSO. will require furtherinvestigations; the soil, a red yellow planosol, was moderately acid, and highlygranular. Under such conditions, gaseous loss of N from tho ammonium source wouldnot be expected.

The TS.R.A. values correlated highly with % NDFF, and a function based onyield - fertilizer N uptake; (grain and straw) (see figures 2 and 3); the 'r'values were 0.98?, and 0.982 respectively.

The 'A1 value data was not constant for cither carrier, as the rate ofapplication at seeding time was increased from 40, 64 to 120 kg N/ha (Tables 13and 14)« However, where corresponding corrections were made for post emergenceapplications of nitrogen using E.R.A. values for treatment I, and the actualamount applied at the tillering stage for treatment II, remarkably constant 'A1values resulted for the three rates of application applied at seeding time. (Acalculated E.R.A. for the 60 kg N applied to treatment II was not possible sincethis treatment was not sequentially labelled. However, based on the 40-40-40sequence data, the S.R.A. was probably at least 60 kg N/ha).

- 136 -

SUMMARY AND CONCLUSIONS

This paper considers the 'A' value concept, and its application to fieldexperiments using labelled 'nitrogen and phosphorus carriers. Extensive referenceis made to phosphorus experiments carried out in, Saskatchewan, Canada, and theJoint PAO/lAEA's international field fertility research programmes on rice andwheat, using N-15 labelled carriers.

The only assumption, indigenous to the 'A* value concept, is that when twosources of a given nutrient are present in a soil, a plant will absorb fromeach in proportion to the respective quantities available. Where the fertilizerstandard does not, on a relative basis, react with the soil system, '/.f valueswill remain constant as the rate of application is increased. However, labelledP or N fertilizers frequently undergo significant changes in the soil system.Such phenomena do not invalidate the 'A' value concept, but rather, as shown inthe data presented, afford a further, and significant application of. the *Afvalue technique. Irregular behaviour of calculated 'Af values serves as aquantitative index of the influence of many environmental and soil factors onfertilizer and soil nutrient availability.

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REFERENCES

(1) ALEKSIC, Z., BROESHAKT, H. and MIDDLEBOE, V. 1968. The effect of nitrogenfertilization on the release of soil nitrogen. Plant and Soil (in press).

(2) PRIED, M. 1964. 'E', »Lf and »A' values. Trans. 8th Int. Cong. Soil Sci.IV: 29-39.

(3) FRIT-ID, M. and DEAN, L.A. 1952. A concept concerning the measurement ofavailable soil nutrients. Soil Sc. 73: 262-271.

(4) HADDOCK, J.L., HAtfSENBUILLER , B.L. and STANBERRY, C.O., Studies with radio-active phosphorus in soils of the Western States (1950-53).

(5) LEGG, J.O., and STANFORD, G. 1967. Utilization of soil and fertilizer N byoats in relation to the available IT status of soils. Soil Sci. Soc.Amer. Proc. 31: 215-219.

(6) MITCHELL, J., A review of tracer studies in Saskatchewan on the utilizationof phosphates by grain crops. J. Soil Sci. 8 (1957) 73-83.

(7) MITCHELL, J., DEHM, J.E. and DION, H.G. Availability of fertilizer and soilphosphorus to grain crops, and the effect of placement and rate of appli-cation on phosphorus uptake. Sci. Agric. 32 (1952)

(8) RENNIE, D.A. and CLAYTON, J.S. 1960. The significance of local soil typesto soil fertility studies. Can. J. Soil Sci. 40: 146-156.

(9) REUNIE, D.A. and CLAYTON, J.S. 1966. An evaluation of techniques used tocharacterize the comparative productivity of soil profile types inSaskatchewan. Trans. Comm. II and IV. Int. Soc. Soil Sci., Aberdeen,365-376.

(10 ) RENNIE, D.A. and MITCHELL, J. The effect of nitrogen additions on fertilizerphosphate availability. Canad. J. agric. Sci. 34 (1954) 353-363.

(11) RENNIE, D.A. and SPRATT, E.D. I960. The influence of fertilizer placement on'.A1 values. Trans. 7th Int. Congress Soil Sci. IV, Vol. Ill, 535-543.

(12) RUSSELL, R.S., RICKSON, J.B., and ADAMS, S.N. 1954. Isotopic equilibriabetween phosphates in soil and their significance in the assessment offertility by tracer methods. J. Soil Sci. 5: 85-105.

(13) SCHMEHL, W.R., OLSEN, S.R., GARDNER, R. , ROMSDAL, S.D. and KUNKEL, R.Availability of phosphate fertilizer materials in calcareous soils inColorado, Agric. Exp. Station, Fort Collins (1955 )•

(14) SPRATT, E.D., and RENNIE, D.A. 1962. Factors affecting and the significanceof 'A1 values using band placement. "Radioisotopes in Soil-Plant NutritionStudies", I.A.E.A., 329-342.

(15) TERMAN, G.L. and KHASAWNEH. 1968. Crop uptake of fertilizer and soil phos-phorus in relation to calculated 'A' values. Soil Sci. 105: 346-354.

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TABLE 1COMPARISON OF BAUD AND MIXED PLACEMENT OFA WATER SOLUBLE FERTILIZER (NH H?PO.)ON 'A' VALUES (KG P/HA) FOR FOUR SOILS

Rate of Application Soil Typekg P/ha • Chemozemic Solonetzic

I II I II

A) NH4H2P04

22 mixed44 mixed22 banded44 b'andedL.S.D. (P = .05)

•

30.434.3

' 17.416.74.0

76.886.051.551.07.4

74.575.0r.

29.733.86.8

11312676.272.2

5.6-

Source; Rennie and Spratt (ll)

. TABLE 2THT5 INFLUENCE OF INCORPORATED WHEAT 'STRAWQJ. AVAILABLE SOIL PHOSPHORUS (.'.A1 VALU.ES)

Placement ofNH4H2P04

mixedmixedbandedbanded

Soil Amendments

150 kg N/ha40,000 kg straw/ha 5 400 kg N/ha

150 kg N/ha40,000 kg straw/ha; 400 kg N/ha

L.S.D. (P = .05) .

'A' valuekg P/ha

12616772.052.416.0

Source: Rennie and Spratt (ll)

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TABLE 3CONSTANCY OP 'A' VALUES (KG P/HA) USING SEED PLACEMENT OP NH.HpPO.WITH INCREASING FERTILIZER P APPLICATIONS(FIELD EXPERIMENT)Rate ofapplicationkg P/ha

Soil typeChernozemic - Si. CL Calc-Chernozemic - L.

2.65.210.521.042.0L.S.D. (P = .&5)

2630282625ns

1924232322ns

Source: Spratt and Rennie (14)

TABLE 4THE 'A' VALUE AS AN INDTO OF PLANT AVAILABLE PHOSPHORUS

IN SELECTED SUB-GROUP SOIL PROFILE

Sub-groupprofile type

yield NaHCO,

'A1 value (pptn)increase from , / extractableP fertilization^ P (ppm)

Calcareous

Orthic

Eluviated

Glysol

dry2/wet—'drywetdrywetdrywet

li/123512 '437281041

III/515525321424

I5629471184324847

II194382555 "466242

I8101717810

o 2425

II2822273024241615

Sourcet Rennie and Clayton (9)profiles developed on glacial till chernozcmic blackprofiles developed on glacial till chernozeiric dark brown

-<25 cm of stored moisture plus precipitation>33 era of stored moisture plus precipitation

II^drywet

3/v<yield increase x 100check yield

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TABLE 5THE INFLUENCE OP SOIL MOISTURE STRESS ON PLANTGROWTH AND 'A' VALUES (GROWTH CHAMBER EXPERIMENT)

MoistureRegime(% Water)272727L.

- 17- 14- 9S.D. (P = .05)

Grain Yield(g/Pot)

12.59.13.20.8

1 h ' value(kg. P/ha)

6141257

SourcetSpratt and Rennie (14)

TABLE 6EFFICIENCY OF VARIOUS MONO- AND DI-HYDROGEW PHOSPHATE

CARRIERS USING 'A' VALUES AS AN INDEX (MEANS OF 6 EXPERIMENTSFOR THE YEARS 1961, 1962 and 1963)

Phosphate Carrier

NH4H2P04(NH. )_HPO.KH€P04

K2HP04

NaH2P04Na2HP04Ca (HJP04)2CaHP04

'A' Value(kg P/ha)

35.236.748.651.342.448.0 -55.0

612.0

E.R.A.- /kg P/ha

as NH4H2P04

20.019.214.513.716.614.6- •12.81.1

RelativeTSfficiency(*)10095726883

. ..?3695

Source: Data from University of Saskatchewan experiments,using spring wheat as the test crop.

2/ E.R.A. = Effective Rate of Application, calculatedas by Rennie (11)

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TABLE 7

•A' VALUE AS AN INDEX OP THE N-SUPPLYINGCAPACITY OP SOILS (GROWTH CHAMBER STUDY)

Soil type

Evesboro siRedbay siMiami silElliot clCrosby cl

Initial N(ppm)

95017110231

Aj,.( value(ppm)

105122 .;. .207271439

$ Yield

4049707993 •

udata selected from a list of 12 soils;Source; Legg and Stanford (5)

Soil from

TABLE 8'•A'" VALUE DATA (PPM) - RICE

(GREENHOUSE EXPERIMENTS)Rate ..of N. application, kg N/ha

50 100 . 200U.A.R.BrazilRomaniaAustria

12361

.15977

12255 .16291 .

1166116383

Source: Aleksic et. al. (l)

- 142 -

SABL3 9"EFFECT OP PLACEMENT^/ OP (NH )SO ON EFFICIENCY

OP UTILIZATION OP FERTILIZER^ BY RICE

Country

U.A.R. IU.A.R. IIBurmaPhilippinesHungary

1 A ' value ,Surface

3543241010512226

Depth

367240360294174

T3.R. A. -surface-'kg/ha

12489436972

SoilPH

8.27.94.96.16.7

—' The"(NH y S'OV was applied at 120 kg/ha at planting time,in rows, on the surface, and at a depth of 5 cm.2/—' Calculated from N-15 assay of final grain samples

—' E.R.A. = effective rate of applicationSource: Joint FAO/IAEA's 1965 co-ordinated rice experiments.

TABLE 10CALCULATIONS - EFFECTIVE RATE OF APPLICATION (E.R.A.)

Placement of N

SurfaceDepth

. $> N in the grain A,, valuederived from |kg/ha)

Fertilizer-P Soil-P

27.0 73.0 32433.3 • 66.7 240

Assumptions:1^ the surface A,, value is high due to loss of fertilizer N;2) the depth A— value is more nearly correct than an approximation

of the E.R.A. for the surface treatment isfert.N x A^ value : 27. x 240 « 89 kg/hasoil N 73

- 143 -

TABLE 11CALCULATED EFFECTIVE RATE OF APPLICATION (KQ N/HA) 6P SELECTED

NITROGEN CARRIERS COMPARED TO AN (NH4)2S04 STANDARD -'

Location ofExperiment

urea NH*N03

I Applied at'5 cm depth at planting time-'U.A.R. 120 " 116 44 25'Burma 120 99 48 15

II Applied 2 weeks before primordial initia^ion(on surface)

U.A.R. 132 186 105 33Burma "12? 114 112 79

•i/ All carriers applied at a rate of 120 kg N/3aajdata from N-15 assay on final grain samples

Source: Joint FAO/IAEA co-ordinated rica fertility experiments

N Source

TABLE 12LABELLED N FIELD EXPERIMENT, BRAZIL, 1968/69

Treatment- / % Ndff Fertilizer NUptake kg N/ha(grain + straw)

«A' Value (Grain) E.R.A.- /kg N/ha kg N/ha as

faase = 87)

NaNO, 40*-40 -40 -40*-40 -40 -6o*-60 -120*- 0 -

(NH4)2S04 40*-40 -40 -40*-40 -40 -60*-60 -120*- 0 -

404040*0-0404040*00

32.39133574 -243722958

34.239.66.636.2 .69.022.931.81.727.453.3

8563268111

. ..42 ...12768

I96014787

415513482482751235120

* N-15 labelled nitrogen sourcei/ 40-4 -40 » N banded at seeding - topdrossed at tillering - topdressed at

the boot stage•2/32/68 x 87 = 41 etc.Source: Contract No. 623, A.M.L. Neptune, Piracicaba, Brazil

- 144 -

TABLE 13»A» VALUE DATA PROM 1968/69 N-15 LABELLED FIELD EXPERIMENT IN BRAZIL

NaNO, used as source of nitrogen

Treatment-^/ % NDFF^/ '/.' Value Calculated E.R.A.-'grain kg N/ha kg N/ha

(grain) (base - 42)

Corrected . /'Af value-'

I 40*-40 -40- 40*-40- 40 -

II 60*-60 -III 120*- 0 -

404040*00

3239133574

Si6326811142

2027623120

51--

SL42

Labelled NaNO,i/.40-40-40 = N banded at seeding - top-dressed at tillering - top-dressed atthe boot stage.

ercentage nitrogen in the grain derived from the fertilizer.?'/32/68 x 42 = 20 etc.

4/85 - (27+6) = 52; 111 - 60 51.Source* Contract No. 623, A.M.L. Neptune, Piracicaba, Brazil.

TABLE 14«A« VALUE DATA PROM 1968/69 N-15 LABELLED FIELD EXPERIMENT IN BRAZIL

SO. USED AS SOURCE OF NITROGENTreatment-'

I 40*-40-4040-40*-4040-4n-40*

II 60*-6C-0III 120*-0-0

*Labelled (NH 'I/ 4i/ 40-40-40 = I

' SHDFPgrain

243722958

»2S04r banded at a

•A' Valuekg N/ha(grain)12168

I96014181

(eedinsr - to-od]

Calculated E.R.A.kg N/ha

(base = 87)27512

35120

r-essed at tillering —

Corrected-'''A' value

84

SI81

tondreaand at the

2/—'boot stage

—'percentage nitrogen in the grain derived from the fertilizer.•2/24/76 i 8? = 2? etc.4/127 - (51+2) = 84; 147 - 6u = 87.Source: Contract No. 623, A.M.L. Neptune, Piracicaba, Brazil

- 145 -

JIWSNCE 0."' A N7mW>f*,K*l !)KiiH€TBNnv ON ' A' "AU.TO =?(>»1!^ 0? PHOSPHORUS :-'RRTTl.T7<l7TON

200

UO

110

tt » 36 «Ib M PER ACRE

(11)

, aCi

Figure 2.

£ 90

f 805 70zo» 60

:•

W 40302010

Calculated 'Effective Rate of Application* (E.R.A.')closely approximates the percent nitrogen in thegrain derived from the fertilizer (NDFF)

Figure 3. R lationship between 'E.R.A.', and fertilizer N uptake(based on grain plus straw yield functions)

o o

00

o>

UJ

o * actual rate of applicationx s effective rate of application

10 20 30 40 50 60 70 80 90•/. N OFF

10 20 30 40 50 60 70 80 90 100FERTILIZER N UPTAKE kgN/ha

PATE OF FERTILIZER NITROGEN APPLIED TO SOILSJ.O. Legg

U.S. Department of Agriculture, Beltsville, Maryland, U.S.A.

ABSTRACT

15A review of recent research involving N as a tracer indicates anacceleration of experimental work concerned with the fate of fertilizer nitrogenapplied to soils. Factors influencing the efficient utilization of appliednitrogen, including placement, timing of applications, nitrogen sources andrates, and crop cultural conditions, have been examined. These factors are alsorelated to nitrogen losses, which vary greatly with experimental conditions.Several studies of 15u-labelled fertilizer which has "become immobilized in thesoil organic fraction indicate that the 5n is incorporated into organic formssimilar in composition to a large fraction of the indigenous soil nitrogen in arelatively short time.

- 146 -

1. INTRODUCTION

Expanded use of chemical fertilizers provides one of the means by which thegap between world food production and population growth can be decreased. Inmany areas the production and distribution of chemical fertilizers do not meetthe current needs of agriculture; therefore, the efficiency with which theavailable fertilizer is used becomes a critical factor. This is particularlytrue in the case of nitrogen fertilizer, since nitrogen is susceptible tonumerous biological and chemical transformations which may lead to rapid lossesfrom the soil, or to conversion of mineral nitrogen into relatively unavailableorganic forms.

Much of the present knowledge concerning nitrogen in soils has been broughttogether in a monograph by Bartholomew and Clark (?)• This monograph hassummarized and evaluated a number of various aspects of nitrogen research, andserves as a guide in projecting future research. Allison (2, 4) has alsoreviewed earlier research concerned with the fate of nitrogen in soils. It willbe the purpose of this report, therefore, to review only the more recentliterature pertinent to the subject matter, and to discuss briefly some datarecently obtained in the author's current research programme.

2. FERTILIZER NITROGEN IN THE SOIL NITROGEN CYCLE

Aliison (3) presented a rather complete diagram of the nitrogen cycle whichpermits an overall view of the possible reactions involved when fertilizernitrogen is added to soil. This diagram is broadly divided into three sections:nitrogen sources, transformations, and utilization. Part of the nitrogenentering the system from fertilizer sources may be quickly removed by plant uptake,A portion of the nitrogen removed by plants may be recycled into the systemthrough crop residues and manures, resulting in a lower net removal and a con-version of inorganic nitrogen into organic forms. The fertilizer nitrogen notremoved by plants is subject to immobilization by microorganisms and to lossesthrough denitrification and leaching. All of these processes involved areinterrelated, but some separation will be made for the purpose of discussion.

3. PLANT UPTAKE OP NITROGEN

The usual purpose of adding fertilizer nitrogen to soils is to obtain maximumyield and quality of crops within certain economic restrictions. Maximum utili-zation of applied nitrogen by the crop is an important consideration in attainingthis purpose. Furthermore, as more fertilizer nitrogen is utilized by the crop,less remains in the soil system for possible loss or immobilization by micro-organisms.

It is generally recognized that 50$ or less of applied nitrogen is usuallytaken up by a crop, although this figure may vary considerably. A number ofrecent experiments with 15N have been directed toward increasing the efficiencyof nitrogen utilization by plants through better placement and time of applicationof the fertilizer (l, 11, 1?, 18, 21, 42). Much of this work has been concernedwith rice production and, to a lesser extent, with maize.

- 147 -

Rice presents some unique problems with respect to nitrogen nutrition. Sub-merged soils develop two distinct layers: a surface oxidizing layer of a fewmillimeters thickness, and a deeper surface layer which is in a chemicallyreduced state. Surface-applied ammonium nitrogen is subject to nitrification andsubsequent denitrification; however, if the ammonium is placed in the subsurfacelayer, it is less likely to be chemically altered. Prom this standpoint alone,placement of nitrogen in rice culture assumes an important role.

The recent data obtained by Aleksic _et_ al_. (l), shown in Table I, illustratethe recovery of u-labelled (NH ) SO. by rice in greenhouse tests. It is quiteevident from the data that placement at 7-cm depth resulted in increased nitrogenuptake and decreased nitrogen loss, although plant growth was not always increasedby the increase in nitrogen uptake. The reduction in gaseous losses obtained byplacement at shallow depth approximately accounts for the increase in nitrogenutilization.

Broadbent and Mikkelsen (ll) obtained a significantly lower grain yield ofrice from broadcast applications than from other types of placement. Recoveryin the plants varied from 26 to 47$ of the labelled nitrogen, with highestrecoveries from banded plus topdressing and from banded treatments at the highest(NH.)p SO. rates (about 60 ppm N). Fertilizer nitrogen losses ranged from 6.5 to30.5$. Highest loss was from topdressed urea in split applications, and lowestloss was from banded

Time of application is also important in placement studies. 'Patnaik andBroadbent (42) found that 51$ of "the nitrogen topdressed at the boot stage wastaken up by plants as compared with 32$ of the nitrogen topdressed at tillering.This is possibly related to the particular type of root growth that occurs at theboot stage. No report was given of nitrogen loss in this case.

The results given above are in general agreement with those reported earlierby Fried (21 ) and by the International Rice Research Institute (25). Anotherfactor involved in some of the studies reported is that nitrogen from (NH.)2SO.is generally used more efficiently by rice than is nitrogen from urea, althoughyields may not be affected,

Cho j|t_ al . (17, 18) have recently conducted field experiments with N,using maize as the test crop. The soil in the experiment was not low in availablenitrogen, and they found no yield response; however, there were differences inuptake of the applied nitrogen. In early stages of growth, more nitrogen wastaken up when the fertilizer was placed near the plant, but these differencesdecreased with maturity. Utilization of the applied nitrogen increased with ageof the maize, and amounted to approximately 30 to 40$ at maturity.

In a non-tracer field experiment with maize, Olson et al. (37) demonstratedthat utilization of nitrogen applied at 40 and 80 Ibs/acre was greater with summersidedressing than with fall or spring application. For example, at the 40-lb/acre rate, 25$ of the nitrogen was utilized from fall application, whereas 58$ wasutilized by plants summer sidedressed. In a separate field experiment theyrecovered (in the grain) 77$ of the nitrogen, applied at the rate of 40 Ibs/acresidedressed, compared with a low recovery of 37$ from 160 Ibs/acre fall applied.

- 148 -

Recent work on a series of isotopic studios concerned with the uptake ofnitrogen "by pasture plants has been reported by Vallis et_ al. (52) and byHenzell ot_ al_. (24). In these studies inorganic and organic nitrogen sources,

• respectively, were used, In both cases a legume and Ehodesgrass were grownseparately and together. Grown separately, the legume and grass took up aboutequal amounts of *5N. When grown together, the grass was a very strong compe-titor for available nitrogen. Little nitrogen was transferred from the legumeto the associated grass. Simpson and Preney (45) worked with three pasturesoils of different organic matter contents and obtained 80$ recovery 4f labellednitrate nitrogen by three cuttings of ryegrass from two soils. Ammoniumnitrogen was immobilized rapidly, especially in the low-nitrogen soil, and thusplant recovery was lowered. Other plant uptake studies will be considered inthe following section.

4. NITROG5N LOSSES

Nitrogen losses from fertilizer applications to soil may be generallyclassified as gaseous losses or leaching losses. Quantitative determinationsof such losses are not easily made directly, since a controlled atmosphere isusually required in the former, and a lysimeter in the latter type of loss.Most of the data concerning gaseous losses has been determined indirectly asthe difference between fertilizer nitrogen added and that recovered in the soiland plants, where leaching has been prevented. An account of the fertilizernitrogen balance is thus obtained.

The use of N as a tracer allows precise measurements of fertilizernitrogen in the soil-plant system, especially in greenhouse tests. Field testsmay also be used successfully to determine nitrogen balance (15, 36) by usinga micro-plot system (small areas within cylinders forced into the soil). Inthe latter case careful soil sampling is of the utmost importance. Morerecently, gas lysimeters have been devised which allow measurements of bothgaseous and leaching losses (34, 39, 43).

Volatilization of ammonia from soils will not be considered here to anygreat extent. Other gaseous losses are generally considered to result primarilyfrom denitrification. Such losses occur quite commonly, even in well-controlledgreenhouse experiments, as evidenced by deficits in nitrogen balance sheets.Water movement in some soils may be slow enough to create small waterlogged areasin which denitrificatinn can occur readily. Frequent waterings required ingreenhouse experiments accentuate this condition. A number of other factorspossibly involved in gaseous nitrogen losses have been discussed recentlyelsewhere (4, 10).

One might expect that denitrification would be decreased by increasedcapacity of a soil to fix ammonium, since fixed ammonium is not readily availableto microorganisms. Recently, Atanasiu et al. (6) carried out several nitrogenbalance studies with 5]j»iabelled ammonium and nitrate sources, applied to soilshaving different ammonium fixation capacities. After growing oats in Mitscherlichpots, losses were found to be as much as 30$ of the applied nitrogen} however,there was no clear-cut relationship between ammonium fixation and nitrogen loss.In one experiment nitrogen losses were higher with both nitrogen sources on asoil of high fixation capacity as compared with a soil of low fixation capacity.In the case of ammonium, the difference in nitrogen loss was small (14$ vs. 12$)

- 149 -

between the high- and low-fixing soils, In another experiment, their data showconsiderably less nitrogen loss from a high-fixing than from a medium-fixing soil;however, there was little difference between nitrogen sources, indicating thatammonium fixation was not a particularly important factor. Furthermore, thelower plant uptake of nitrogen from the medium-fixing soil approximately accountsfor the difference in nitrogen loss between the high- and medium-fixing soils.

Gasser et al. (22) determined nitrogon losses from applications of labelled(NH.)pSO,. and Ca^NO, )„, with and withovt the nitrification inhibitor 2-chloro-6--(tnrichloromethyl)-pyridin3., +o four -loc'.od soils. Two of the soils were fromold arable fields, and two were from grassland. One soil of oach set had a pHof about 5, while the othors had a pH of about 6. In the first part of theexperiment the treated soils were incubatod in pots for 6 weeks. Essentiallycomplete recovery of -^H was obtained upon analysis of the incubated samples.Lowest recovery (94$) was from (NH.)pSO. after 6 weeks1 incubation; after subse-quent cropping with ryegrass, recovery $as lowest (86$) with Ca(NO,)_ applied tograssland soil. Influence of tha nitrification inhibitor was minor.

Results of other recent nitrogen balance studies are given in Table II. Itis difficult to generalize regarding nitrogen losses where soils, nitrogensources and rates, and experimental conditions vary considerably. If the dataare representative, however, loeses can b^ expected to exceed 20$ of the nitrogenaddition about 5*"*$ of the time. Where the investigators compared nitrate andammonium sources, the data indicate that losses from nitrate were neither consi-stently higher nor lower than those from ammonium. Carter et al. (15) andZamyatina t_ al. (55» 56) found no difference between the two sources duringcropping, and Broadbent and Nakashima (13) found losses from urea to be essentiallythe same as those from nitrate sources. Under submerged conditions, of course,nitrate nitrogen may be completely lost in a very short time as shown by MacRaeet al. (33).

Martin and Ross (34) conducted a nitrogen balance study, using labelledfertilizer in a gas lysimeter. They reported negligible gaseous losses of Np,NpO, and NH,, and obtained an average recovery of 100$ of the added 15fl from thesoil-plant system. Overrein (39) conducted a somewhat similar type of experiment,using 15u-labelled urea, and found the highest total accumulated loss of NILequal to 3.5$ of the added nitrogon. Other gaseous losses of nitrogen were foundonly in trace amounts. During the 12-tfeek experimental period in which the totalprecipitation was about 3?0 mm: the -iccuiralated loss by leaching was slight aturea application rates less than 250 kg/ha. Leaching loss from a 1000-kg/ha ratewas equal to 5$ of the added nitrogen,

Leaching losses of N-leboiled nitrogen have been evaluated recently byTakal:ashi in conjunction with lysimeter and field studies of nitrogen uptake bysugarcane in Hawaii (48, 49, 50, 51). Usually, from one-third GO one-half of theapplied nitrogen was re-covered in the plant mate-rial, including leaf trash andth•-; succeeding ratoon crop, Takahashi considered that most of the nitrogenremaining in the soil after crop growth was immobilized in organic forms and thatlittle leaching occurred. In the lysimeter experiments (50, 51), the Nconcentration of the percolates was very low; however, the amount of soilinorganic nitrogen in percolates vas relatively high during the first month ortwo of plant growth, and throughout the experiment in fallow lysimeters. Thispoints toward the importance of actively growing plants in reducing leaching losses.

- 150 -

Methods other than those involving conventional lysimeters have been usedin recent years to study the downward movement of nitrogen. Wagner (53) estimatedleaching by the porous cup method, designed to sample internal drainage waterswithin the soil profile. Water samples collected periodically during 4 yearsindicated that a significant amount of nitrate nitrogen had leached through thesubsoil on plots^treated with 200 or 400 Ibs/acre of nitrogen. Total nitrate inprofiles of fertilized plots decreased with time, and after three successivesudangrass crops, it was as low as that in control plots. About 35$ of theapplied fertilizer was recovered in the sudangrass.

Krause and Batsch (28) used tension-plate lysimeters placed at the 30-cmdepth to study the movement of fall-applied nitrogen in a sandy soil at Ontario,Canada. They treated the 15-cm surface layer of soil with NH.NO, at the rate of112 kg/ha and collected leachates at weekly intervals. In 2 to 3 months' time,the applied nitrogen moved almost completely to the 30-cra layer, primarily in thenitrate form. Apparently, nitrification of ammonium proceeded rather rapidlyunder suboptimum conditions.

Prom the "foregoing it is easily seen that fertilizer nitrogen losses fromsoils may be quite large and difficult to control under experimental, as well aspractical, conditions. Broadbent and Clark (10) and Parr (41) have discussed thepossibilities of eliminating gaseous nitrogen losses, but at the present time,except in special cases, this does not appear to be economically feasible.

The nitrogen losses shown in Table II took place primarily during short-termexperiments. Broadbent and Clark (10), however, consider that losses taking placeat low rates over long periods of time arc; probably of greater significance. Theslower losses are presumed to result from denitrification in anaerobic or nearlyanaerobic microareas of otherwise well-aerated soils. Denitrification lossesresulting from the movement of nitrates downward into the lower part of the soilprofile are probably insignificant (10) owing to the low energy supply for denitri-fiers. Downward movement of nitrates is also more likely to take place duringseasons when plants are not actively growing and temperatures are low.

The movement of mineral nitrogen downward, however, may effectively remove itfrom the root zone, and once it is below the roots there is little evidence thatappreciable movement upward occurs, at least in humid regions. Little informationis available on the fate of mineral nitrogen under natural conditions, once it isleached beyond the root zone. Investigations along this line will probably beaccelerated in the near future, owing to the increased use of nitrogen fertilizersand their possible accumulation in ground water.

5. IMMOBILIZATION-MINERALIZATION REACTIONS

From Table II it can be seen that the fertilizer nitrogen remaining in thesoil after cropping amounts to 20$ or more of the application rate in most cases.I-Iost of the residual fertilizer nitrogen, particularly after exhaustive croppingin -i;he greenhouse, is immobilized in organic forms and becomes slowly available tosubsequent crops. The amount of inorganic fertilizer nitrogen that is transformedinto organic forms, and the rate at which it is mineralized have been subjects of anumber of recent investigations.

- 151 -

The nitrogen transformations in soils that lead to the immobilization ofapplied inorganic nitrogen are not completely understood, but use of *5]J as a tracerhas produced some very useful information in this regard. Basically, it is knownthat mineralization-immobilization reactions proceed simultaneously, and thatmeasures of either reaction arc essentially net differences between the two reactions.When a state of equilibrium exists, no change will be observed in the inorganicnitrogen content, although microbiological activity continues. Normally, however,either immobilization or mineralization predominates, and measurable changes occur.The C/N ratio of most soils is such that in the absence of fresh additions of anavailable carbon source, the soil organic matter is slowly decomposed duringincubation under aerobic conditions, liberating part of the carbon as CO,,, and theorganic nitrogen as mineral forms. The C0? is largely dissipated into the atmo-sphere, while the mineral nitrogen accumulates in the soil, usually in the nitrateform.

Jansson (26, 2?) has pointed out that accumulated nitrate forms a passive poolof mineral nitrogen in soil which is not recycled into immobilization-mineralizationreactions. If soil conditions are such that net immobilization occurs, however,nitrate will not accumulate to any great extent, and addod nitrate nitrogen willbe immobilized (9). On the other hand, when -^H-labelled nitrate nitrogen isadded to soils in which net mineralization is occurring, it can be recovered almostcompletely in the mineral form after 30 or 40 days of incubation (8, 31). Onemight expect that plants could effect similar recrovs ries however, as shown by Leggand Allison (30) from 10 to 36$ of the nitrogen from 15n«iabelled NaNO, remainedin the soil after exhaustive cropping of the same soils that were used in the incu-bation experiment. Insofar as possible, roots were excluded from the soil analysesby removal at the end of the experiment. Only 2 or 3$ of the labelled nitrogen wasaccounted for by the harvested roots from the last crop. Such results emphasizethe effect of the growing crop on the immobilization of fertilizer nitrogen in thesoil. This effect can be explained on the basis that plant roots are contributingavailable carbon to soil microorganisms throughout the growth period, and thatmineral nitrogen is immobilized in microbial tissue. The amounts of nitrogeninvolved are usually too large to be accounted for in roots not removed from thesoil.

The influence of the root system on microbial activities has been recognizedfor many years; however, there is considerable disagreement on the magnitude ofthe contribution of roots to the energy supply of microorganisms during the plantgrowth period. Such contributions may have been underestimated. Recently,Samtsovich (44) presented data indicating the presence of transparent gel-likesubstances on the root tips of a number of plants. This substance forms a protec-tive zone around the root caps, meristom, and elongation areas, and is abundantlyfilled with plant cells which continuously disengage f.rom the root caps. Thematerial is invisible if unstained, but becomes quite distinct in tho microscopeif the roots are stained with methylene blue or gentian violet. Samtsevich esti-mated the volume of the gel-liko substance produced by wheat and maize, and con-cluded that even if the material contained only ifo dry matter, during the vegetativeperiod plants exude into the soil via their roots at least as much dry matter as isproduced in high yields of the crops (7 metric tons/ha for wintor wheat and 12.5tons for maize). He suggested that the amount of excretions is even greater,especially for perennial plants. Tosts for sugars, amino acids, proteins, andstarch were negative for the substance obtained from maize, but the test for hemi-cellulose was positive. More work in this area should lead to a greater under-standing of the plant effect on fertilizer immobilization in soils.

- 152 -

Immobilization of -%-labelled nitrogen accompanying the incorporation ofplant residues, such, as straw, into soil has been of continued interest to anumber of investigators. Broadbent and Tyler (14) studied the effect of pH onnitrogen immobilization from 15n-labclled NH.C1 and KMO,, added to two soils withor without 0.5$ straw. The ammonium sourco was used to a greater extent bymicroorganisms at all pH levels, but there was a marked influence of pH on thequantity immobilized. Ammonium nitrogen immobilization increased with an increasein pH, whereas the reverse was true of tho nitrate sourco. The results appearedto be related to the physiological acidity or alkalinity of the nitrogen source.Analyses of acid hydrolysates indicated that most of the nitrogen incorporatedinto the organic fraction was present in the amino form.

A number of other factors involved in nitrogen immobilization have beenstudied. Overrein and Broadbent (40) and Overrein (38) have investigated theinfluence of temperature and nitrogen sources on immobilization-mineralizationreactions involved in the decomposition of forest litter. Preferential utiliza-tion of ammonium was found regardless of soil temperature in the range of 40 to90 F. In some soils the nitrifying microbial population was able to competeeffectively for'ammonium with the hcterotrophic microflora, and considerablenitrification took place.

Increases in immobilization of nitrogen in soil by additions of organicmatter with high C/N ratios have been observedfor many years. Usually the C/Nratio of the decomposing material must be below 20 to 25 (about 1.5 to 2$ N) inorder for appreciable net mineralization to take place. In some recent work withsubmerged rice soils, Williams _et_ al_. (54) observed net nitrogen immobilizationto be only 0.54$ of the original dry weight of added rice straw as determined bygrain yield responses. This lower value was attributed to the anaerobic environ-ment of the flooded soil which resulted in incomplete decomposition of the carbo-naceous material. In this experiment, carried out without tracer nitrogen, nosignificant immobilization of supplemental nitrogen resulted from straw applications,

Danneberg et al. (19) studied the transformation of N-labelled ammoniumduring aerobic decomposition of chopped maize leaves for periods up to 180 days.They found that the added ammonium was immobilized in organic compounds mainlyduring the first 10 days. The largest amount was in a "protein" fraction, thetotal nitrogen of which increased up to 30 days, indicating a marked synthesisof microbial protein. This fraction decreased later as microbial substancesdecomposed. There was also a marked synchesis cf humic substances, especially inthe early part of the incubation, as indicated by an increase in the acid-insoluble"humin" fraction; however, this fraction contained a relatively small amount oflabelled nitrogen. This experiment was carried out in the absence of soil, andwas somewhat similar to a decomposition experiment with oat straw, reported byKuo and Bartholomew (29). They concluded that essentially all of the nitrogen inthe plant material had been mineralizedj therefore, it may be surmised that theremaining organic nitrogen resided primarily in microbial tissue. Their conclusionwas based on the fact that the tracer contents of tho organic and inorganic phasestended to approach equivalence as a result of nitrogen interchange.

The equivalence of labelled nitrogen in soils has been studied in plant uptakeand mineralization studies by Broadbent and Nakashima (12). In their experimentsa quantity designated as "availability ratio" was calculated according to theequation:

- 153 -

. TcU + TAvailability ration = c c

TsUs+Ts

where T = tagged N in plant material (or in mineralized N from incubations),CU = untagged H in the corresponding material above,CT = tagged N in soil at beginning of vegetative or incubation period,sU « untagged N in soil at the same time.If the tracer nitrogen in a soil has the same availability to plants or

microorganisms as the soil nitrogen, the availability ratio will be unity. Onthe other hand, if it is more available than soil nitrogen, the ratio will begreater than unity. Broadbent and Nakashima (12) found that in successivecuttings of sudangrass, availability ratios ranged from 11.9 i*1 the secondcutting to 1.2 in the seventh cutting of plants grown on Yolo soil. The ratioswere decreased by the addition of straw to the soil. In incubation testslasting up to 592 days, several ratios below 1.0 were obtained, but for themost part they were between 1 and 2 during the latter half of the experiment.

Recently, Legg (unpublished) carried out a long-term greenhouse experimentin which -^U-labelled (NH,)pSO. was incorporated into the soil organic matterby successive cropping with oats. The plant material was returned to the soil,except for pots which were removed from the experiment at the end of eachcropping period. Plant material and soil from «ach sot of triplicate pots wereanalysed for total and 15n-labelled nitrogen. The results, calculated in termsof availability ratios, declined from an initial value of 10.4 to approximately2 at the end of the experiment. Soil samples obtained after 2, 5 and 8 croppingperiods were incubated at 35°C and leached with 0.01 IJ CaCl, (followed by -Nsolution) at bi-weekly intervals for 40 woeks. The availability ratio, calcu-lated for the mineralized nitrogen at each.incubation period, gradually declinedfor the second-crop soil until it was approximately 2; thereafter it remainedessentially constant. For the fifth- and eight-crop soils, little change wasnoted in availability ratios which remained somewhat above- 2 throughout theincubation period. The data suggest ohat in relatively short interchange periodsinorganic nitrogen applied to soils may be converted to stable organic formswhich are similar to the indigenous organic nitrogen. It could be speculatedthat with a soil having a stable availability ratio of 2, one-half of theindigenous soil organic nitrogen is essentially inert owing to physical or bio-chemical inaccessibility to microorganisms.

Stanford e_£ al_» (47) subjected samples of the fifth-crop soil mentionedabove to repeated extractions with boiling 0.01 ft CaCl,, (100 C), or autoclaving(121°C), or both, to study the behaviour and properties of immobilized fertilizernitrogen relative to soil organic nitrogen. They found the distribution of 15Namong chemical fractions of the hot-water extracts, acid hydrolysate, and acid-insolublu portion to be similar to the distribution of indigenous soil nitrogen.Since appreciable equilibration between added - jj Q^^ the more resistant formsof soil organic nitrogen appeared unlikely, it was postulated that the fertilizernitrogen reacted to form new compounds, similar in composition to pre-existingforms of soil nitrogen. This view seemed in harmony with the observation thatthe percentage removals of total and ^-%_iabeiie(j nitrogen by repeated extraction

- 154 -

wore almost identical, even when recoveries by hot-water extraction attained55$ or more.

Using the same soil, Tout different frac^ionation and extraction procedures,ChiChester (l6) found evidence to support the hypothesis that the labelled andunlabelled forms of organic nitrogen are similar in composition. He initiallyseparated the organo-mineral components of the soil into separate size fractionsby wet sieving and centrifagation without using chemical dispersing agents.The resulting silt-size separate was then subjected to repeated 15-minute ultra-sonic vibration treatments, followed by centrifugation to separate the clay-sizematerial which resulted from the physical dispersion. The separates wereextracted with 0.5 N, sodium pyrophosphate at 100 C, and the extracts werefractionated into distillable, acid-hydrolyzable, ninhydrin-reactive, andresidual nitrogen components. Some of the results obtained in this study,presented in Figure 1, illustrate the similarity in composition of the labelledand unlabelled fractions for the different treatments.

It appears highly significant that biological, chemical, and physicalmethods lead to the same conclusion concerning the fate of immobilized fertilizernitrogen in soil. Although it is not possible to go into'the details of theabove research in this report, it appears likely that findings of this naturewill have considerable influence on our basic understanding of immobilization-mineralization reactions, and on the projection of new research in this area inthe near future.

6. CONCLUSIONS

Tremendous progress in nitrogen research has been made in recent yearsthrotigh the utilization of -^H as a tracer. The number and variety of experi-ments conducted have provided a wealth of information concerning the fate offertilizer nitrogen in soils under many different conditions. In many cases thisinformation is of direct practical importance in the efficient regulation of thenitrogen nutrition of plants. The magnitude and importance of nitrogen lossesfrom soils have been clearly depicted by the use of - u,.and new methods arebeing devised to -3tudy this complex problem. Transformations of inorganic ferti-lizer nitrogen into organic forms in soil produce compounds which appear similarto indigenous soil organic nitrogen in a relatively short period, according toseveral-recent experiments. Further research on nitrogen transformations insoils should be accelerated by these recent advances.

- 155 -

REFERENCES

(1) ALEKSIC, A. _et al., Shallow depth placement of (NH SO, in submerged ricesoils as related to gaseous losses of fertilizer nitrogen and fertilizerefficiency, Plant and Soil 2£ 2 (1968) 338^

(2) ALLISON, F.E., The enigma of soil nitrogen balance sheets, Adv. in Agron.I (1955) 213. V

(3) _______ • Evaluation of incoming and outgoing processes that affectsoil nitrogen, Agron. J.O (1965) 573.

(4) ,' The fate of nitrogen applied to soils, Adv. in Agron. 16(1966; 219. ' .

(5) ANDREEVA, E.A., SHCHEOLOVA, G.M., Utilization of nitrogen fertilizers byplants (Experiments with 15N isotope), Pochvovedenie (19.64) 47 (in Russian),

(6) ATANASIU, VON N. e£ al_. N-Bilanzrechnungen mittels % im N-Mngungsverf ahr en.(7) BARTHOLOMEW, W.V., CLARK, F.E., eds., "Soil Nitrogen", Agron 10_ (1965).(8) BROAUBEtIT, P.B., Effect of fertilizer nitrogen on the release of soil

nitrogen, Soil Sci. Soc. Amer. Proc. 29 (1965) 692.(9) ________, Interchange between inorganic and organic nitrogen in soils,

Hilgardia 3J_ 6 (1966} 165.(10). _____. CLARK, F.E., Benitrification, Agron. 0£ (1965> 347.(11) ________, MIKKELSEH, E.S., Influence of placement on uptake of tagged

nitrogen by rice, Agron. J. 60 (1968) 674.(12) _____ , MAKASHIMA, T., Reversion of fertilizer nitrogen in soils, Soil

Sci. Soc. Amer. Proc. 31 5 (196?) 648*(13) . .___ . ________ , Plant uptake and residual value of six tagged

.nitrogen fertilizers (Sorghum sudanensis, Lycopersicon esculentunu Zeamays), .Soil .Sci. Soc. Amer, Proc, 32 3 (1968)- 388. :

(14) _________, TYLER, K.B., Effect of pH on nitrogen immobilization in twoCalifornia soils, Plant and Soil 23 3 (1965) 314.

(15) CARTER, J-»jJ. e£ al ., Recovery of fertilizer nitrogen under field conditionsusing ^N-labelled fertilizers, Soil Sci. Soc. Amer. Proc. 31 (1967) 50.

(16) CHICHESTER, F.W., Transformations of fertilizer nitrogen in soil. II. Totaland •'•5N-labelled nitrogen of soil organic-mineral sedimentation fractions.(Submitted for publ.).

(17) CHO, CHAI MOO e± al_., ^N field experiment with maize within the frameworkof an international program, Trans. 8th Intern. Congr. Soil Sci.,Bucharest, Romania IV (1964) 87.

- 156 -

(18) __________ .et al., The effect of placement on the utilization of nitrogen•"by maize as determined with 15ii-labelled ammonium sulphate. In: Procof the Symposium on Isotopes in Plant Nutrition and Physiology, 5-9 Sept.,1966, Vienna, Austria (196?) 47.

(19) DANNE3ERG, O.K. et_ al. , Transformation on -%-labelled ammonium duringaerobic decomposition of plant material. Proc, of Symposium: IsotopeStudies on the Nitrogen Chain, Vienna, Austria (1968) 89.

(20) DINTSCHEFF, D» , Untersuchvngfcn tlber die Stickstoffverluste im Boden unterAnwendung des stabilen Isotops - N, Trans 8th Intern. Congr. Soil Sci.,Bucharest, Romania IV (1964) 1C05.

(21) PRIED, M., Report on the 1964 and 1965 results of the joint PAO/IAEA Divisionsco-operative research programme on rice fertilization using isotopetechniques. Intern. Rice Commission — Working Party on Rice Soils, Waterand Fertilizer Practices — Lake Charles, La. (1966),

(22) GASSER, J.K. jet_ al^ , Measurement of losses from fertilizer nitrogen duringincubation in acid sandy soils and during subsequent growth of ryegrass,using 15N-labelled fertilizers, J. Soil Sci, 18 2 (196?) 289.

(23) GIRBUCHEV, I., DIHCHEV, D,, The use of ^N in the study of nitrogen uptakeand metabolism in plants, Proc. of the Symposium: Isotope Studies on theNitrogen Chain, Vienna, Austria (1968) 63. (in Russian).

(24) HHfZELL, E.F. et_ aj . , Isotopic studies on the uptake of nitrogen by pastureplants. Uptake of nitrogen from labelled plant material by Rhodesgrassand oiratro. Aust. J, Agr. Res. 19 1 (1968) 65.

(25) INTERNATIONAL RICE RESTSAHCH INSTITUTE, Annual Report, Los Banos, Laguna,Philippines (1965)

(26) JANSSON, S.L., Trace? studies in nitrogen transformations in soil withspecial attention to mineralization-immobilization relationships. Kgl.Lantbruks-Eogskol. Ann, 24 (1958) 101-

" f*

(27) _________ , Nitrogen transformation in soil organic matter, Rpt. FAO/IAEATech. Meeting on the Use of Isotopes in Soil Organic Matter Studies,Braunschweig (1966) 283,

(28) KRAUSE, H.H, BATSCH, W_, Movement of fall-applied nitrogen in sandy soil.Can. J. Soil Sci. 48 (1968) 363.

(29) KUO, M.H., BARTHOLOMEW, W,V. , On the genesis of organic nitrogen in decom-posed plan^ residue, Rept, FAO/IAEA Tech. Meeting on the. Use of laotopesin Soil Organic Matter Studies, Braunschweig (1966) 329.

(30) LEGO, J.O., ALLISON, F.E. , A tracer study of nitrogen balance and residualnitrogen availability with 12 soils, Soil Sci. Soc. Amer. Proc. 31 3(1967) 403. "~

(31) ____ ; ____ , STANFORD, G. , Utilization of soil and fertilizer N by oatsin relation to the available N status of soils, Soil Sci. Soc. Amer.Proc. 3JL 2 (1967) 215. . .

- 157 -

(32) _____________ j3t_ al. , The influence of microorganisms on the degree ofassimilation of nitrogen by plants from soil and fertilizer., Izvest.Timiryaz. Sel'khoz. Akad. 1 (1966) 22. (in Russian).

(33) MacRAE, I.C. et al_. Pate of nitrate nitrogen in some tropical soilsfollowing submergence, Soil Sci, 105 (1968) 327.

(34) MARTIN, A.E., ROSS, P.,0., A nitrogen-balance study using labelled fertilizerin a gas lysimeter, Plant and Soil 28 (1968) 182.

(35) MERZARI, A.H., BROLSHART, H. , The utilization by rice of nitrogen fromammonium fertilizers as affected by fertilizer placement and microbiolo-gical activity, Proc. of the Symposium: Isotope Studies on the NitrogenChain, Vienna, Austria (1968) 79.

(36) NOMMIK, Bans, Use of micro-plot technique for studying gaseous loss ofammonia from added nitrogen materials under field conditions, Acta Agr.Scand. 16 (1966) 147.

(37) OLSON, R.A, _e£ al_. , Controlling losses of fertilizer nitrogen from soils,Trans. 8 th Intern. Congr. Soil Sci., Bucharest, Romania IV (1964) 1023.

(38) OVERREIN, L.N., Immobilization and mineralization of tracer nitrogen inforest raw humus. I. Effect of temperature on the interchange ofnitrogen after addition of urea-, ammonium-, and nitrate- N, Plant andSoil 27_ 1 (1967) 1.

(39) __________ , Lysiraeter studies of tracer nitrogen in forest soil: I.Nitrogen losses by leaching and volatilization after addition of urea-l5jS, Soil Sci. 106 (1968) 280.

(40) __________ , BHOAEBENT, P.E. , Immobilization and mineralization of tracernitrogen in soils of northern California, Trans. 8th Intern. Cong. SoilSci., Bucharest, Romania III (1964) 791.

(41) PARR, J.P., Biochemical considerations for increasing the efficiency ofnitrogen fertilizers. Soils and Pert. 30. 3 (1967) 207.

(42) PATNAIK, S,. , BROADBEUT- P.E,, Utilization of tracer nitrogen by rice inrelation to time of application, Agron. J. 2 3 (1967) 287.

(43) ROSS, P.J., .et. al_- , A gas-tight growth chamber for investigating gaseousnitrogen changes in the soil: plant :atmospere system, Nature, Lond. 204(1964) 444.

(44) SAMTSEVICH, S.A,, Active excretions from plant roots and their significance.Fiziol. Rast, JL£ 5 (1965) 837. (in Russian).

(45) SIMPSON, J.R. , FREffEY, J.R., The fate of labelled mineral nitrogen afteraddition to three pasture soils of different organic matter contents,Aust. J. Agr. Res. 18 4 (1967) 613.

(46) SMIRNOV, P.M. et_ al, , Transformation of different forms of nitrogen ferti-lizers in soil and their utilization by plants (according to experimentswith 15N), Izvest. Timiryaz. sel'khoz. Akad. 2 (1967) 85. (in Russian).

- 158-

(47) STANFORD, G. £t. .al.., Transformations of fertilizer nitrogen in soil. I.Interpretations based on chemical extractions of labelled and unlabellednitrogen. (Submitted for publ.).

(48) TAKAHASHI, D.J. ^N-nitrogen field studies with sugarcane. Hawaiian PlantersRecord 52. 2 (1964) 198*

(49) ' '' ''" '" • Pate of applied fertilizer nitrogen as determined by the use of-ON.I. Summer and fall plant and ratoon crops on the Hamakua Coast ofHawaii. Ibid 52. 3 (196?) 23?.

(50) _______, Effect of amount and timing on the fate of fertilizer nitrogenin lysimeter studies .with N, Ibid 57 4 (1967)"292.

(51) _______, Fate of ammonium and nitrat.e fertilizers in lysimeter studieswith -ON, Ibid 58 1 (1968) 1.

(52) VALLIS, I. JB_£ al., Isotopic studies on the uptake of nitrogen by pastureplants. Ill, The uptake of small additions of l^N-labelled fertilizerby Rhodesgrass and Townsville lucerne\ Aust. J. Agr. Res. 18 6 (1967) 865.

(53) WAGNER, G.H., Changes in nitrate N in field plot profiles as measured by theporous cup technique, Soil Sci. 100 .6 (1965) 397.

(54) WILLIAMS, W.A. et_ al^, Nitrogen immobilization by rice straw incorporated inlowland rice production, Plant and Soil 28 1 (1968) 49.

(55) ZAMYATINA, V.B. et_ al., The use of "^N f or the study of transformations ofnitrogen fertilizers in soil and their utilization by plants, Sonderdruckaus "Isotopenpraxis" 3_ (1967) 62. (in Russian). • '

(56) ________, et^ a.1 ., The use of N in studying the conversion of nitrogen-ous fertilizers in.soil and tks utilization" of nitrogen by the plant.Rept. FAO/IA'EA Tech. Meeting on the Use of Isotopes in Soil Organic MatterStudies, Braunschweig (1966) 307.

- 159 -

Table-1. Shallow depth placement of (NH.)pSOj. in submerged rice soils as relatedto gaseous losses of fertilizer nitrogen and fertilizer efficiency(Aleksic et_ al. (l)).

Soils

Thailand

Burma

Philippines-

Madagascar

Ceylon

U.A.R.

Treatments

surfacedepthsurfacedepthsurfacedepthsurfacedepthsurfacedepthsurfacedepth

Plant Weight(g)

12.010.0

11.514.217.315.06.04.98.59.59.8

11.2

IT recoveryin plants

% of N apj(150 mg/!

496545663750354943611939

Gaseous Nlosses

jliedjot).

28153519391527111776442

- 160 -

Table II. nitrogen balance experiments with 15K as a tracer.

spI

Investigators

Dintscheff [20]Andreeva and Shcheglova [5]

Zamyatina et al. [55]

Legg et al. [32]Legg and Allison [30]

Carter et al. [15]

Crop

——fallow

ti

oatsrye

!t

millet oatsnfallow(40-60 days)oatsoats andsudangrassfallow11sudangrass

K recovery ($)K source

<»Uaso4KNOa(MB* )sSQiKN03(KB4)2S04Anion-N03KHOsHH» -cation(HEt)8SQi

(MH SQtKNGj(RHj )gS04

KKOg

NaN03HaNOgHaUOg(NHi)s S04

in

UT

42586856513245

16

57•

3226

plants

- 56....71- 52- 67- 70- £•>- 55- 51" 4

IV W * ••

• ™ *•

- 8c

- 85

- 55- 59

in

245455jj'j

19232221

222259609

1099P7-4o

soil

- 31- 84" 72- l£- 3^» *-f .4.

12- 24- ?5- 45- 29- 80- 69- 11

- 36- 100- 98- 69- 64

N loss (#)

161628231131523222420311100200

- 25- 46- 1*514- B9_ ^- crC- 22- 2k

- 2?- 26- 41- 4o- 15- 18- 1- 3- 4- 4

Continued

Tatle II. Continued.

Zamyatina et al. [56] corn (NtOa30*" NaHQs

oats (UIJj )2 S04" KE03

barley (KHi)2S04

Sraimov _et £l. [46] oats NaIT03" (NKi )a SO".l? »» • "Urea" 15JJILNO,' KB^lorJC^

fallow NaJJQjl! (H^)aS04

jf- Mersari arid Broeshart [35] rice IC^Cioo- Broadbent and Miiucelsen [11] rice (HHjJgSi^i " Urea

Broadbent and Makashiaa [13] 3 crops - (KHiJs^sudangrass, lsMKIICa"tomatoes., and K^ N03corn KtK)3

KHjOHUrea

55612245

5758535651-

-

-L^

2926

353858603553

- 61- 63- 51• 5^-53'

- 59- 6l- 61- 59. 59_ _ _—

- 52\ —

- 33

- 56- 62- 71- 70~ 37- c4

19172222

81014175-368

29

4236

22262423IB30

- 23- 20- p4- 2930

- 9- 12

~ £

— J.C-- 8- 64- 74

- 39

• i?

- 26- 33- 33- 32- 25- 4l

20192224

33292523333!-2c

9£+*•

2?11

~

£7

35c"

- 22- 20• 27- 2617

- ~-f:- 30- 31- 27- 38- 47

- 32_ c-

- 15- 31

- 39- 29- 1C- 8- 47• os

Girbuchev oats l£ - 25

TOTAL N 15N-LABELLED N

015 60 130 015 60ULTRAS :.C VldR; J1OH TREATMENT, MINUTES

(I) NaOH-Distiliable N Prior to Acid Hydrolysis *(I) NaOH-Disti!lab!e N Following Acid Hydrolysis of Residue from I(Jtt) NaOH-Distillable N Following Ninhydrin Reaction of Residue from I A

(E) Total N of Residue from H A

(Y) Non-Extractable by Na Pyrophosphate ft

Fig. 1. Distribution of sodium pyrophosphate-extractable nitrogen of£ 53 IA soil part.1.cie-sizo classes in relation to intensity of xiltrasonic

vibration treatment received prior r-c fractionation (Chichester [16]).

- 160 c -

THE USE OP N-15 AS A TRACER IN FERTILIZER EFFICIENCY STUDY IN JAPAN

Susumu NishigakiSoil Fertility Division

Department of Soils and FertilizerNational Institute of Agricultural Sciences

Nishgahara, Kitaku, Tokyo, 114 Japan

Crop plants are most sensitive to nitroggn among many other essentialnutrients. Application of nitrogen is considered at first to stimulate the plantgrowth.

The nitrogen fertilizers are given to the crops throngh the soil, and thefertilizer nitrogen is subjected to chemical and biological changes in the soil.So the uptake efficiency of fertilizer nitrogen is not always high enough forthe efficient crop production.

It becomes very important to know the uptake efficiency of dressed nitrogenin the crop. The. conventional method of determining fertilizer uptake efficiencyis based on the difference in uptake of nitrogen by a crop between no nitrogenand nitrogen dressed plots.

However, from two points of view at least, the conventional method doesnot seem to be very exact. Firstly, dressed nitrogen stimulates the root growth,and the roots in the nitrogen dressed plot naturally spread in bigger volume ofsoil and take up more soil nitrogen from the soil than in the plot where nitro-gen is not given. So the above-mentioned difference in the amount of nitrogentaken up in the two treatments will include nitrogen from both sources of theapplied fertilizer and the soil itself. Secondly, the conventional method isnot provided with any device to distinguish soil nitrogen from fertilizernitrogen.

If the stable (non-radioactive) nitrogen isotope, N-15 in a form of nitro-gen fertilizer, is used as a nitrogen fertilizer to be tested in one plot offield experiment, one can identify and determine the amonnt of fertilizer nitro-gen :. uptaken by the crop, as the amount of N-15 isotope in a crop is measuredwith mass-spectrometer and by the tracer method.

Thus "the uptake efficiency of dressed fertilizer nitrogen" can be accura-tely determined in a field experiment. This is the first problem to be solved toimprove the method of fertilizer application to a crop, and the use of N-15isotope made this possible.

To obtain a good yield, nitrogen taken up by crops should contribute to thegrowth of proper organs in a stage of crop growth. N-15-labelled nitrogenfertilizer can be determined in any organ and in any growth stage of crops.

The percentage of N-15-labelled nitrogen in the total nitrogen in ai organat growth stage will furnish information on the contribution of nitrogen ferti-lizer to the crop production. Therefore, it is sometimes called "the contribu-tion rate of nitrogen fertilizer" in an organ at growth stage of a crop.

This is the second problem to be solved for the improvement of fertilizerapplication method.

- 161 -

Many methods of determining soil nitrogen fertility have developed, andthe results were found to be in good correlation with uptake of soil nitrogenby crops. Further, many attempts have been made to determine the rate ofnitrogen fertilizer application using the data of soil nitrogen fertility] Theidea, in which the late of nitrogen application should be determined consideringthe rate of soil nitrogen fertility is undoubtedly correct, and these attemptsseem to be successful for the crop culture of moderate yield.

But the attempt is considered to be useless for crop culture higher yield.The problem is supposed to exist in one point, that is, the relation betweenthe time of emergence of soil nitrogen and the time when the crop requirementof nitrogen depending on the different growth stages- The partial efficiencyof absorbed nitrogen differs at different growth stages, and in some casesabsorption of much nitrogen in one growth stage can decrease the crop yield.

*»

Prom this point of view, one should know not only the time of nitrogenrequirement by crops but also should know the time of absorption of soil nitro-gen. Then it becomes possible to determine the time and rate of nitrogen appli-cation for a crop to obtain higher yields. Tracer methods using N-15-labellednitrogen fertilizer can tell not only the amount of fertilizer nitrogen absorbedbut also the amount of soil nitrogen absorbed by the crop plants. If the plantsample is taken and analysed for N-15 and total nitrogen of plants several timesthroughout the crop life of the N-15 tracer field experiments, amount of soilnitrogen utilized by crops in each stage of growth can be determined. Thus thepattern of the utilization of soil nitrogen by crops can be easily known, andthe rate and time of nitrogen application can be determined referring to thepattern of nitrogen requirement of crops through the whole life cycle.

This is the third problem to be solved to improve the method of nitrogenfertilizer application to a crop using N-15 isotope.

Prom these above-mentioned points, (l) the uptake efficiency of dressedfertilizer nitrogen, (2) the contribution rate of fertilizer nitrogen in anorgan at a growth stage of a crop, and (3) the time pattern of utilization of-=soil nitrogen by crop, N-15 stable isotope has been used in Japan for researchto improve the method of nitrogen application on rice plants, barley, soybean,sugar beet, onion, green house tomate, mandarin orange trees and persimon trees.

The results of these rese.aro.hes done in field experiments were very fruitfuland they have been already put into farmer's practices.

1. TECHNICAL PROBLEM IN N-15 PISLD EXPERIMENTS

(l) Nature of N-15 IsotopeThe stable isotope of N-15 is contained in the natural nitrogen at the per-

centage of 0.37, and it does not have radioactivity. N-15 tracer technique doesnot raise any radiation hazard problem. It can be used in any field experimentin .the farmer's field, where food is produced.

Radioactive isotopes will decay and decrease in amount in process of time,but N-15 is stable and it does not decay. So, in principle, tracer work can beperformed as long as the expriment is needed.

- 162 - .

Isotope of N-15 can be easily used in double-labelled tracer technique withother stable isotopes such as C-13, H-2, 0-18 and so on, and also radioactiveisotopes without disturbing the determination of other stable and radioactiveisotopes. In many cases, double-labelled fertilizer using N-15 and P-32 is common-ly utilized in the field tracer experiment, because of the importance of bothnitrogen and phosphorus in the crop production and because of the interaction ofboth wktrients in the plant physiology.

Isotope of N-15 does not decay as mentioned above, so the experiment field,once used for N-15 tracer, cannot be used again for N-15 tracer work, otherwisethe second tracer experiment will be disturbed by the residual N-15, whi h wasplaced in the former.field tracer experiment. The place of plot, in which N-15was given, should be accurately registrated.

In the tracer field experiment using N-15 several hundred grams or kilogramof labelled nitrogen fertilizer will be needed, and the unit price of N-15-labelledfertilizer is not cheap, so the field N-15 tracer experiments need much greaterfunds than ordinary field experiments.

The determination of N-15 in the nitrogen requires mass spectrometry orparticular ligat spectrometry, and the instruments needed are very expensive.The methods of determination are also more complicated than chemical analysis andradiation counting.(2) Production and Distribution of Stable Nitrogen Isotope N-15

Stable nitrogen isotope is made by concentrating N-15 °f natural nitrogen(0.376$ N-15 and 99.624 N-14). Many concentrating methods have been developed andsmall-scale production •-• started in many countries in 1£4?. At present, N-15isotope is produced in Japan, the United States of America, United Kingdom, France,Canada, USSR and some other countries, and it is easy to purchase N-15 isotopesas a commercial product in any part of the world.

N-15 isotope-labelled fertilizers in the form of ammonium sulfate, ammoniumnitrate, sodium nitrate, urea, and in some other forms are available for fertilizerexperiments. The labelling concentration of N-15 isotope in the available ferti-lizer nitrogen ranges, from 3$ to 99$ and it is called "abundance of N-15 isotopein the fertilizer nitrogen".

Labelled fertilizer having more abundance of N-15 is used in the tracerexperiment, the higher precision is easily obtained in the results. 'But the priceof one gram of N-15-labeled fertilizer goes up exponentially with the increase ofabundance of N-15 isotope in fertilizer nitrogen, as for example, the market priceof N-15 labelled ammonium sulfate fertilizer is shown in Pig. 1.

Although the N-15 labelled fertilizers are expensive, small-scale fertilizerexperiments such as water culture and soil pot experiments do not cost much. Inthe case of field experiments, trouble may be caused by the cost of the experiments.Suppose, a field fertilizer is to be conducted, and the application rate of nitrogenfor rice culture is 100 kg per hectare. That is 10 gram of nitrogen or 5Q gramof N-15 labelled ammonium sulfate will be required for each square meter of theplot in the experimental field. If ammonium sulfate labelled7 by 30 per cent ofN-15 abundance is used, the cost for the- isotope will be around 600 dollars persquare meter of the plot. But if ammonium sulfate labelled by 3 per cent N-15abundance is used, the cost will be only around 33 dollars. Thus it is better to

- 163 -

use low N-15 abundance nitrogen as far as possible in field fertilizer experiments,from the standpoint of experimental costs. In Japanese field experiments onfertilizer efficiency, labelled fertilizers of 2$, 3$, 5$, 7 and 10% N-15abundance are commonly used.(3) Determination and Tracer Method in the Use of N-15

Nitrogen in plant materials has .to be converted into nitrogen gas before N-15abundance is determined. As to the method of IT- gas generation from plant samplesthere will be two at least. In the' first method, plant materials are decomposedby Kjeldahl method into ammonia and' the resulting ammonia is converted into N«gas by hypobromide reagent. In the second method, nitrogen in plant sample isdirectly converted into N? gas by Duma method.

To determine N-15 abundance in the N? gas, mass spectrometer or molecularphoto-spectrometer can be used.

Tracer radioisotopes, for example P-32, are not contained in the naturalelement like phosphorus, but stable isotopes, for example N-15, are contained innatural elements, for example in natural nitrogen, in small abundance. So thetracer calculation for N-15 tracer method is somewhat more complicated than inradioisotope tracer method. To simplify the calculation, "the excess percentof N-15 in nitrogen" is considered, which can be obtained by subtracting^ naturalabundance of N-15 in natural nitrogen, for in example C.367, from abundance oforiginal N-15 labelled fertilizer nitrogen and in nitrogen of. plant sample, asshown below:

Source of Nitrogen Abundance % access % ofof N-15 N-15

Natural Nitrogen 0.36? 0Original Nitrogen inlabelled fertilizer 5.231 4.864Nitrogen of plant sample 0.975 .608

If it is the case shown above, isotope dilution ratio will be 8, which is obtainedby dividing 4.864 by 0.608, and this is the same tracer calculation as radioisotopetracer method.

Here a problem comes up; how one can select proper abundance per cent of N-15in the fertilizer nit.rogen to be used. Table I will show some idea to selectabundance per cent of N-15 labelled nitrogen fertilizer for field fertilizerefficiency experiment. This table was made basing on many Japanese experiencesof 18 years since 195 . Table I also shows that the required abundance per cent ofN-15 in fertilizer nitrogen will depend on the standard deviation of the N-15determination very close to the natural abundance of 0.36?. Namely, the higherprecision of N-15 determination'will permit.the lower abundance per cent of N-15in nitrogen fertilizer, thus the lower cost for labelling nitrogen fertilizers.

Consequently, one has to know the precision of N-15 determinations beforeone can plan the design and N-15 abundance of field tracer experiments.

- 164 -

II. AN EXAMPLE OF N-15 TRACER FIELD 13XPERIMENTS ON NITROGM FERTILIZEREFFICIENCY

It had been a common practice to harvest rice in summer and wheatin winterfrom paddy field in Gifu Prefecture in the middle part of Japan. National demandfor vegetable production and farmer's demand to increase their income requiredto replace the winter wheat by winter onion in late 1950» B«it a trouble happenedin the rice culture after -.onion. Rice yield decreased and the cause was supposedto exist in excess nitrogen uptake by rice plants.

To investigate this problem, a series of tracer field experiments was con-ducted. Successive N-15 tracer field experiments of onion-rice plants, wheat-rice plants and rice culture were conducted in 1957-58. The root activity distri-bution in the soil of the field was determined on onion and wheat in 1959-1960.

As a result of the study, new placement of nitrogen fertilizer was establishedand the total amount of nitrogen applications for onion was reduced to 130 kg/hafrom the conventional application rate of 190 kg/ha. The new method was put intothe farmer's practice, and a fertilizer cost of 100,000 dollars for onion cultureis saved annually, and the trouble in rice culture was removed in Gifu Prefecture.

The design of N-15 tracer experiment is shown in Table II. In the onionculture, all nitrogen given in Treatment A was labelled by N-15 of 0.891 excessper cent. Nitrogen top dressing of warm season only was labelled by N-15 of2.528 excess per cent in Treatment B. In Treatment D natural nitrogen was givenin all dressings. Treatment H did not receive nitrogen at all. In the wheatculture (Treatment F) labelled nitrogen of N-15 of 0.891 excess per cent was givenin all dressings.

After these winter culture crops were harvested, rice plants were transplantedsuccessively in Treatment A, B, D and F. Treatment A, B, and F, in which labellednitrogen had been given to onion, natural nitrogen fertilizer was given to rice.Treatment D, in which natural nitrogen had been given for onion, N-15 labellednitrogen fertilizer of 3.775 excess per cent was given for rice culture.

All crops obtained very good yields, i.e. over 50 tons/ha of onion, 4.3 tonsof wheat grain and 5»5 tons/ha of hulled rice grain (about 7.5 ton/ha of grainwith hull). The onion culture in Treatment H, in which no nitrogen was applied,yielded 32 tons/ha of onion.

The design of the experimental plots was fixed according to the author's method,in which 1.33 m labelling small plotr. was placed inside the larger plot of 12 m .The boundary between small and large plot was made by thin galvanized iron sheet,and the plants were planted in continous rows without changing the spacing betweenplants, even at the point where the plant row and iron sheet cross each other.This is very important to avoid boundary effects around small labelled plot. Rateof fertilizer dressing was maintained uniformly throughout larger plot and smallplot in it.

The N-15 abundance in the nitrogen of the plants was determined very carefullyto maintain the standard deviation of N-15 abundance at about ± 0.001, when theN-15 abundance was less than 1.000. Actually, N-15 abundance of the plant nitrogenranged from 0.990 to 0.600 in onion and wheat, and from 1.500 to 0.307 in rice plants

- 165 -

The results obtained in tho tracer field experiment is shown in Table III.Nitrogen of 50.8 kg/ha was taken up oy onion and 3.5 kg/ha was takaiup by

rice plant, from 189 kg/ha of whole nitrogen applied for onion (Treatment A).This 3.5 kg/ha uptake by rice plants exceeds 1/10 of 31.7 kg/ha (Treatment D),which was taken up by rice plants from 84 kg/ha of nitrogen given for rice culture.This fact suggests that the residual of nitrogen dressed for onion will causeappreciable effects on the rice plants cultivated after onion.

Nitrogen of 40.9 kg/hs. wr-* taken n?p by who?,t and 1.7 kg/ha was taken up byrice plants out of 94 kg/ha of fertilizer nitrogen given to wheat (Treatment P)»This 1.7 kg/ha taken up by rice plants is only about 1/20 of 31.7 kg/ha (Treat-ment D), suggesting little effect of fertilizer for wheat on the succeeding riceculture.

Table IV shows summarized re-suits of uptake efficiency of nitrogen fromammonium sulfate which was used for three different crops on the same soil typeof Kamosima Series (rice field soil).- The efficiency was highest at 43.5$ inwheat culture, and 37*6$ in rice culture, and lowest at 26*9$ in the onion culture,The amount of soil nitrogen -tilized :ras highest at 76.9 kg/ha in wheat culture,and 74.2 kg/ha in rice culture, and lowest yj! -.(. kg/ha in onion culture. Thesedifferences of utilization of soil nitrogen waa found to be due to deep distribu-:ion of wheat roots in the soil, due to particular absorption of soil nitrogeniinder water-logged condition in tho rice culture and due to shallow distributionof onion roots..

Fertilizer uptake efficiency of different time of split application in theculture of onion was shown in Table IV. The uptake of nitrogen applied in warmseason of March an'1- April showed fairly good value of 32.7$ taking up 26.7 kg/haout of 72 kg/ha of nitrogen dressing. Hut the uptake nitrogen applied in coldseason of November, December and February showed too low efficiency of 26.9$taking up 23.6 kg/ha out of 117 kg/ha of dressed nitrogen. In spite of low rootactivity under the cold temperature, very heavy rate of nitrogen (117 kg/ha) wasgiven to the onion in the conventional method of cultivation, and residual effectof this part of nitrogen dressing on rice culture occupies-2/3 of the totalresidual effect of fertilizer nitrogen for onion on rice culture (Table III,Treatment A, B and X).

The conclusion obtained h-ro we.s thr.t tb<- method and rate of basic end subse-quent top dressings in cold season for onion should be studied. According tothis conclusion, the root activity distribution in the soil was studied on onionand wheat using P--32 in the same experimental place. A new practical method offertiliser applications for onion was designed and the method was subjected under11-15 tracer field experiments again»

Thus the established new method of onion fertilization, in which the placemen'!;of basic dresring is made beside the onion seedlings, not located under them, andtho rate of nitrogen application in cold season was cut down to half. After thinneu method :vas distributed by extension service, onion growers in Oifu Prefecture-saved much oost for fertilizer and the method had no disturbing effect on therice cultures caused by the foregoing onion culture,

- 166 -

III. WIDE USE OP N-15

Because the nitrogen is the most important nutrient for crop, and the methodof N-15 tracers is easy, N-15 tracer experiments on plant nutrition, N-15 tracerfield experiments on fertilizer efficiency and on soil fertility are now conduc-ted in many Federal, Regional, and Prefectural Experiment Stations and soil-fertilizer research laboratories in Colleges and Universities.

A number of excellent academic resolutions in the nitrogen nutrition of thecrops and practical improvements of nitrogen application were achieved.

But the problem left in the N-15 tracer work is that the number of instrumentsto determine N-15 is not sufficient, and also the mass spectrometry is a verycomplicated work. Consequently, the appearance of more easy new methods of N-15determination is hoped for.

- 16? -

Pi«. 1 . 1TORLD PRICE OP AMMONIUM-SULFATELABELLED BY N-15 ISOTOPE

$2001

10€t

S sooeCO

G

OCO

oo

tco•J

$ 0.

(LOR) Percent of N-15 in N

- 16? a -

TABLE I. ABUNDANCE PERCENT OF N-15 IN NITROGEN FERTILIZERTO BE USED FOR FIELD FERTILIZER EFFICIENCY STUDY

Accuracy of H-15 Deternination at thevery close to the natural abundanceCrops

One year cropsRice plants

Upland cropsLong year cropsKandarinorange trees

+ 0.03 + 0.01 + 0.003Tice of application of labelled nitrogen. .. ,,- _,,„„,,„,. ._ „•„ n*4.^~f>n(Part of labelled nitrogen in total ? iii™ »*«>««»nitrogen application in one crot> or year) v

Lab ell all nitrogen(Basic and all top dressing)

Lab ell one dressing only(Anong basic and top dressings)

Labell all nitrogen to see residualnitrogen absorbed by next cope.

Conditions given above

Labell all nitrogen in one yearOnly one tine of dressing is labelledamong several application in a year.(Other time application is givennatural nonlabelled nitrogen)Long tarn tracer experiment over one yearto sun up long tern absorb tion by plant(Labell all nitrogen is labelled only in firstyear)

10&152y&

3*&?.0#

1.5K

5%Not ffluo]-. difference shov/n _,above for each, condition

i15?:20$

50%

&7%

•#•15#

2%

5%

7%

orI

1) Generally upland soil will give smaller amount of soil nitrogen than rice soil lowerabundance % of N-15 can be used for upland crops than for rice plants.

II THE DESIGN OF N-15 FIELD TRACER EXPERIMENT ON NITROGEN FERTILIZESEFFICIENCY IN ONION AND WHEAT CULTURE "FOLLOWED BY RICE CULTURE

Name of treatments

NotationNumber of duplication"*-—• - _ V/interPlacement*— - ^ . ^ cropsDressing """"""' — - —

1/ol

use

ason

llC

lfff

l

seas

on

Basic Dres. Nov. 161st Top Dres. I/ec. 202nd Top Dree. Feb. 263rd Top Dres .March 184th Top Drca. April 14

Total Nitrogen AgpJLirsdSummerNumber of crops

duplicationBasic Dres. June 231st Top Dres. July 152nd Top Dres. Aug. 53rd Top Dres. Aug. 26

it&l Nitrogen Applied

Whole nitrogenforonion labelled*

A0 J

Onionkg/ha

'46

3636

K-15 0.891 ex.N-15 0.891 ex,N-15 0.891 ex,N-15 0.891 ax.N-15 0.391 ex,

Warm seasondressednitrogenfor onionlabelled

B5

Onion

Natural NNatural NNatural NN-15 2.528ex.N-15 2.528ex.

Wholenitrogenfor ricelabelled

D&' '••"Onion

Natural NNatural NNatural NNatural KNatural N

No nitro-gen foronion

H3

Onion

No NitrogenNo NitrogenNc ritrogenHe NitrogenNo Nitrogen

189

1928289

Rice plant3

Natural NNatural NNatural NNatural N

Rice plant3

Natural NNatural NNatural NNatural N

Rice .plant2

N-153.775 ex.N-153.775 «*•N-153.775 ex.

N-153.775 ex.

"\

\

Whole nitro-gen for wheatlabelled

F5

Wheatkg/hi47 '

47

-

N-15 '0.891 ex.IT-150.891 ex.

-94Rice plant

3282828 .9

Natural NNatural NNatural NNatural N]

93 HNote: ex. means excess percent

oI

TABLE III. FERTILIZER NITROGEN AMD SOIL NITROGEN ABSORBED BY CROPS(Shown in Kilogram per Hectar of Nitrogen)

Name of treatment

Notation

V/in

ter

cult

ure

Oni

on o

r W

heat

• Su

mm

er c

ultu

reR

ice

plan

ts

Nitrogen Total Ntaken up Labelled Nby plants Natural NLabelled nitrogenapplied*

Uptake efficiencyof applied nitrogenNitrogen Total Ntaken up Labelled Nby rice Natural NplantsLabelled nitrogenappliedTotal nitrogenapplied for twocropsUptake efficiencyof applied nitrogen

Wholenitrogenfor onionlabelled

A104.450 J353.6189.26.9*109.124105-6

0

189. ( onion

1.9*

Warm seasondressed ,nitrogenfor onionlabelled

B105.9§H02.372.

32.7%119.51.1llO

0

72. (onion)

1.5*

Cold seasondressednitrogenfor onioncalculatedfrom A and B

X104.427.277.2117.23.2*115.02.4

112.6

0

117. (onion)

1.2*

Wholenitrogenfor ricelabelled

D104.00

104.40-

105-931.774.2

84.3

84. 3( rice)

37.6*

No nitro-gen foronion

H42.4 '042.40

-

-

-

-

-

Whole nitro-gen for wheatlabelled

F'117.S40.97T7994.43.5115.03.13T30

94. (wheat)

1.8?£

II—»op.I

Note: Total fertilizer nitrogen applied for onion was 189 kgAa in A,B, and D. 0 kg/ha in H.Total fertilizer nitrogen applied for wheat was 94 kg/ha in F.Total fertilizer nitrogen applied for rice plants was 84.3 kg/ha in A,B, and D. 94.3 kg/ha in F

TABLE IV. SUMMARY OF UTILIZATION OF SOIL NITROGEN AND FERTILIZER» NITROGEN BY ONION, WHEAT AND RICE PLANTS

Kind of crops

Yield

Total nitrogen taken up

Fertilizer nitrogen

Soil nitrogen

Rate of nitrogenapplication

Fertilizer uptakeefficiency

Onion

50 tonAa (bulb)

104.4 kgAa

50.8 kg/ha

53.6 kc-'ha

189 kgAa

26.9 %

Applied out" Coldseason

23.6 kg/ha

117 kgAa

23.2 %

Warmseason

27.2 kgAa

72 kgAa

32.7 %*»

Wheat4.3 tonAa(grain)

117.8 kgAa

40.9 kgAa

76.9 kgAa

94 kgAa

-.3.5*

Rice plants5.5 tonAa(brown rice)

31.7 kgAa

7L 2 kg/ha

84.3 kgAa

37.6 %

o-J(DI

RADIATION TECHNIQUESAS MEANS OP IMPROVING THE EFFICIENCY OF WATER USE

"byY. Barrada

I. INTRODUCTION

Frequently it is a water shortage, especially at critical periods of cropgrowth, that is the main cause of low yield. Rainfall, even if the total amountis sufficient, is very often so inadequately distributed among the seasons ofthe year, that its valae for agriculture is seriously limited.

Irrigation schemes are nowadays much more common, being made either themajor source of water or a supplement to the natural rainfall. Compared withdry-farmed land, the area of irrigated land is rather small, but its importanceis great as its yields of food and fibres are relatively high. Increases of 30tto 50* in crop production were repeatedly observed after the introduction of anirrigation system. However, despite the growing water shortage problem, theefficiency of irrigation and the efficiency of water use are rather low, andgreat quantities of water are wasted.

A recent F/0 report*) states that "There is no single factor as importantfor saving water as proper use of water on the land". The report goes on to saythat the universal use of proper water techniques would allow for an increase inthe world's irrigated area of 50$ or more, using the same amount of water, andthat the exact determination of the water requirements of plants is a basicprerequisite to proper use of irrigation water.

II. TERMINOLOGY

It might be appropriate to recall the definition of the following mostcommonly used terms to avoid any misunderstanding:Irrigation effioiency.

This is the ratio of the amount of water stored in the ro«t zone, divided bythe total amount applied. Irrigation efficiency takes into consideration thevarious irrigation losses including run off and deep percolation.

*) de MSREDIEU, J. and PILLSBURY, A.F., "Provision for more adequate supplies ofirrigation water". A note for the Working Group of the ECOSOC AdvisoryCommittee on the Application of Science and Technology to Development, FAO-1,Rome (1965) 10.

- 168 -

Bv-apotranspiration (BT) or consumptive use.This is the sum of volumes of water**5 used up during plant growth in trans-

piration and evaporation from soil in any specified time, divided by the area, i.e.aoreXin** = ET (in**) or heotareXcm** = T2T (cm**),acre hectare

Water use efficiency.This is the dry (crop) weight produced per unit volume of water used in

evapotranspiration, i.e.dry weight/acre = dry weight ( tons or tons/m (ST) ).

BT volume of ^H ha, m (ET)If water is expressed in weight then water use efficiency becomes a true ratio

(dimensionless).

III. WATT® USE EFFICIENCY

It should be stated first of all that maximum water use efficiency is notour goal for the following three practical reasons:

Firstly, the cost of practices necessary to achieve higher yields must berelated to their returns in monetary terms. For example, the yield increase fromfertilizers usually follows some kind of decreasing increment function so thateach successive unit of fertilizer produces less<profit than its predecessor.Thus for maximum profit, agriculture must stop short of maximum yield production.As yields stop short of this maximum production, so must water use fall short ofmaximum efficiency. The only adjustment needed in our present thinking on ferti-lizer recommendations, if it is to be based on sound economics, is considerationof how much water could be saved in the production of a certain amount of a givencrop and how this water could be used elsewhere and at what return.

Secondly, there is the problem of utilization of a limited natural watersupply or the availability of water for evapotranspiration. Under dry-land condi-tions all agricultural operations are directed at reducing the rate of evapotrans-piration as much as possible to stretch the available water for production of thegreatest possible amount of salable or usable product. Water use efficiency isfrequently higher under dryland conditions than when irrigation is used.

** Volume of water is in this context usually measured in inches or centimetersper unit surface area.

- 169 -

This higher efficiency of course is attained at a much lower and sometimesdisastrous level of production. Thus water use efficiency cannot be consideredapart from the moisture and yield situation under which it was obtained.

Thirdly, the necessity of applying more irrigation water than is needed inorder to satisfy the leaching requirements for salt removal.

All agricultural practices that increase the ratio of dry weight to evapo-transpiration increase water use efficiency. To investigate, the effects ofcertain farming practices on the efficiency of water use, we must examine theireffects on the actual water use, dry weight production and finally their relativerates of change. The following practices are among the major factors that affectthe efficiency of both irrigation and wateruse (a complete list, of course, wouldinclude almost all the objectives of"agronomic research):1. The control of pests and plant diseases would improve the water use efficien-cy by preventing or reducing crop yield losses (increasing dry weight production).2. Methods that reduce the soil moisture losses due to evaporation and un-necessary transpiration (weed control, mechanical destruction of soil surfacecracks, wind breaks and increased plant population).3. The effects of soil salinity and the various fertilizer salts on root extra-ction of water and on infiltration and run-off cannot be laid aside in anydiscussion of the efficient use of water.4. Fertilizer may increase root development within the soil so that water isused to a greater extent and also from deeper soil layers.5. Evidence indicates that water use efficiency can be greatly increased ifthe application of fertilizers increases yield. Often the deficiency of only asingle plant-food element causes a marked increase in water requirements. Asthe element becomes very scarce the rate of growth as measured by the assimilationof COp is greatly reduced with no corresponding decrease in the transpiration.6. The amount of irrigation water applied and the interval between two successiveirrigations should be determined in relation to different values of soil moisturestorage capacity and the rate of evapotranspiration, so that the harmful effectof draught periods upon crop yields can be minimized.7. As either too much or too little water causes a yield reduction, the rateof water flow throughout the irrigation time should be regulated according to thepermeability of the soil,so that although water infiltrates to the rooting zone,unnecessary losses due to run-off or deep percolation are avoided, and a homo-geneous water distribution is achieved.

In arid and semi-arid regions, the amounts of irrigation water available areso limited, that water is the limiting factor for agricultural production. Undersuch conditions, it is essential to make the best possible use of the water. Toachieve this aim, intensive water use efficiency studies which are prerequisitesfor the development of more efficient methods of water use, are very much needed.Such studies would enable us to achieve the following targetst

- 170 -

(a) On irrigated land, an adequate amount of irrigation water could boapplied, with the proper rate of flow, and at the right time. This wouldreduce wastage of the type mentioned above. The considerable amounts of waterthus saved could be used for improving the water supply of other irrigated areasor for providing an additional area with irrigation water.

(b) The necessity for the improvement of water supply or the need forirrigation water could be quantitatively predicted, so that the necessaryessential information for the planning of new irrigation projects could beprovided.

(c) If experimental results are available, one may assign a definiterecurrence value to the measured yield depression resulting from lack of soilmoisture. Wheh cost of irrigation and increases in gross return are compared,one can estimate the profit that could be expected from a certain irrigationproject over a large number of years.

(d) Through comparing experimental results for various crops and croprotations, the best return for a given amount of water in monetary terms couldbe determined.

In short, water use efficiency studies would lead to the best possible useof the limited amounts of water, and this would in turn increase the productionof food and fibres for a given amount of water. In addition to that, the choiceof crops and crop rotations and a choice of the most profitable irrigationprojects becomes possible, based on sound economics.

Though the importance and great need for water use efficiency studies waswell known to agronomists for a long time, the reports on research work in thisfield are relatively scarce. This is probably because it is difficult and costlyto obtain valid evapotranspiration data, which are the basis for such water usestudies and for comparisons of the effects of various agricultural practices onthe water use and water use efficiency. Field evapotranspiration data are hardto obtain because they require a large number of soil moisture measurements atvarious depths and because of confusing results due to possible losses by deeppercolation and run-off. In fact, many thousands of fertilizer experiments havebeen conducted in which no attempt was made to measure evapotranspiration. Forexample, in most of the more costly factorial experiments in whi,ch irrigationregimes and fertility rates are studied in all combinations, the irrigated plotsare main plots for practical reasons and fertility treatments are sub-plots ofthe split plot design. All fertility treatments in an irrigation treatment areirrigated alike, and in most cases no attempt is made to measure consumptive useon each plot. Actually there are few field experiments that have producedinformation on the "fertilizer-yield, consumptive-use" complex, and most of theseare from studies involving irrigation or from dry-land experiments in which deeppercolation does not complicate the measurements of evapotranspiration.

Methods available for mea9uring soil moisture (other than neutron scattering)are not adequate. These methods are mainly limited to taking samples of the soilfrom various locations and depths in a field to determine the moisture content orto obtaining indirect measurements of the soil moisture by measuring the electri-cal conductivity of the soil or by using tensiometers to measure soil suction

. values.\

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Soil sampling is destructive, time consuming, difficult and arduous work.A great number of samples is needed to ensure that the measurement is represen-tative in addition to the necessity of determining the bulk density.

The resistance methods are not sensitive in the lower soil moisture suctionrange, are affected by the salt content of the soil solution in addition to theshort life expectancy of electrodes imbedded in gypsum blocks and the draft incalibration that occurs with most electrode units. "Because of the logarithmicrelationship between resistance and soil moisture, it is difficult to determinequantitative values of soil moisture content.

The use of tensiometers is very helpful at high soil moisture contentswhere these instruments are sensitive. However, tensiometers cannot measuremoisture conditions in the higher soil-moisture suction range. Like resistanceunits, some difficulty has been encountered in maintaining adequate contact withsoils. Likewise, the readings obtained do not give quantitative values of soilmoisture.

It was with the availability of portable radiation equipment that theproblem of performing large numbers of reliable soil moisture measurements wassolved and the way was opened for intensive water use efficiency studies. Portableradiation equipment is also a very valuable tool for following soil moisturechanges at various depths around the seasons of the year. The information gainedthrough such studies is essential for assessing the need for drainage as well asfor planning adequate drainage systems.

Also the possible effect of various agricultural practices such as growingtrees to serve as wind breaks, associated crops, increasing plant population,hoeing-in the soil surface, mulching and including a period of fallow in thecrop-rotation; on reducing soil moisture losses could very well be investigatedwith the aid of portable radiation equipment.

IV. RADIATION EQUIPMENT

The equipment consists of a "probe" containing the radiation source and thedetector as well as a portable electronic counting unit "sealer" or a "ratemeter". (Fig. l).

The radiation sources most widely used for neutron moisture meters are alphaemitters usually either radium or americium thoroughly mixed with berillium thatfunctions as a target for the alpha particles. The neutron source emits a fluxof fast neutrons as indicated by the following equations-

4 + 9 1 1 2/•if* + ^Be _______^ Qn + I|C + Energy

*The detector is sensitive only to those neutrons that have lost a great deal oftheir original energy through collisions with the surrounding atoms, becamemoderated or slow neutrons and were scattered back to the detector. Usuallyeither a tube filled with borontriflouride gas or a scintillation crystal ofeuropium-activated lithium iodide is used as a slow neutron detector. (Pig. 2).The detection of slow neutrons is based on the following equations:-

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•B + n _______^ Li + He + Energy

^Li + Jn _______v 2He + IH + Energy

gHe + Jn _______v ^P + IE + Energy

For the gamma density probes the radiation sources most commonly used areeither cesium or radium that omit gamma photons. The back scattered gammaphotons are detected by Geiger-Mtlller tubes (Pig. 3).

Surface probes (Fig. 4 and 5) are placed on the soil surface with due careto establish good contact through preparing the location of measurement to beflat, smooth and free of any plant. For depth probes, access tubes usually ofaluminium or steel are placed into the soil, then the appropriate moisture ordensity probe is inserted to the desired depth in the access tube. The sealeror rate meter gives a count rate which varies with moisture or density variations,This count rate is then located on a calibration chart, and the moisture contentor density can be directly read from the chart.

This technique provides many valuable advantages, mainly the following:1. Large volume of material is analysed in a single measurement, as the probesnormally measure an almost spherical volume of soil with an average diameter of40 cm increasing to a larger volume, with a diameter up to 75 cm> in soils ofvery low moisture content or low density.2. With depth probes measurements of moisture content or density can be made atany depth beginning approximately from the top 25 cm of soil.3. Measurements are non-destructive and require no physical or chemical pro-cessing.4. Long term studies of moisture content and density of the same volume of soilare possible. In soil applications, for instance, a permanent access tube can beleft in the ground so that a moisture or density measurement can be made at thedesired depth at any future date.

V. THEORY OF THE ITEUTRON MOISTURE METER

Moisture measurements are based on physical laws governing the scattering andmoderation of neutrons. When a radioactive source of fast neutrons is placed inthe soil, the emitted neutrons collide with nuclei of the surrounding atoms andare scattered randomly in all directions. Each collision by a neutron causes aloss of part of its kinetic energy. The scattering and energy reduction processcontinues for a neutron until its kinetic energy approaches the average kineticenergy of r.toms in the scattering medium. At this lower energy level theneutron is designated a slow neutron.

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The average energy loss by fast neutrons is much greater in collisions withatoms of low atomic weight than in collisions involving heavier atoms, andhydrogen is the only element of low atomic weight found in the soil. Themoisture probe is- constructed with a special detector which is unaffected byfast neutrons and detects only slow or moderated neutrons. Therefore, thenumber of moderated noutrona dotoctcd por unit of time is also a measure of theconcentration of hydrogen atoms in the soil.

Since the hydrogen content of soils is largely contained in the moleculesof water, the slow neutron ccui.t thu:- ocomes a measure of the moisture contentof the soil.

VI. THEORY OF THE GAMMA. DTiNSITY PROBTS

The measurement of density is based on the known interaction of gamma raysand the orbital electrons of atoms. Gamma rays having an energy less than1 MeV emitted by a radioactive source, that is placed in or on the soil, willinteract with the surrounding atoms in the two following ways:

(a) Compton effectIn this reaction the gamma photon acts like a billiard ball, collides •

with an electron and ejects it from its orbit and gives it some of its energyand the photon itself is deflected from its path. The photon thus proceeds ina new direction and with a lesser energy. The energy remaining in the scatteredphoton is available for further interaction with other electrons either bycompton or photoelectric effect.

(b) Photoelectric effectIn this interaction the gamma photon gives up all its energy in the

interaction and coasee to exist. Part of the energy of the photon is consumedin overcoming the binding of the electron in its orbit, the remainder of theenergy appears as kinetic energy of the photo-electron. The photon has to possessenergy greater than the binding energy of the electron but not so much more thanthe electron can take, Photoelectric <ffect is the prinsiple type of reactionoccurring at photon energies up to $£• h.*;. and results in true absorption of theincident photon.

As the number of electrons per unit volume of soil (density) is increased,the scattering power of the medium increases proportionately. With eachscattering process, however, the gamma photon loses some of its energy. Thus,although an increase in electron density of the scattering medium increases theprobability of multiple scattering of the gamma ray, the probability that thegamma photon will be absorbed by photoelectric effect, before it can reach thedetector, is also increased. The combined effect of these two probabilities isthat a smaller number of gamma photons will reach the probe as the surroundingmaterial becomes nore dense.

Since the number of electrons present per unit volume of material isapproximately proportional to the density of the material, the number of gammarays scattered back to and detected by the detector per unit of time is adirectly correlated measure of density.

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The density probe measures the wet density of the soil. Therefore, themoisture weight should be su'btraced, if dry density data is desired.

VII. RESOLUTION OP THE NEUTRON MOISTURE METER

The sphere of influence (ellipsoid) of the neutron moisture meter is thezone of the medium, which effectively contributes to tho observed activity ofthe detector. In practice the radius R of this sphere of influence is determinedthrough lowering the probe (source-detector assembly) into an access tube, intoa homogeneous medium of water content, and taking readings at variable depths.The detector count-rate is plotted as a function of the depth and the radius Ris defined as the depth where the count-rate equals 95$ of the maximum count-rate.The sphere of influence varies with the soil moisture content. Its radiusreaches a minimum of about 15 cm in water (100$) and a maximum of about 40 cmfor very dry soils.

The relatively big soil sample involved in every soil moisture measurementwith the neutron moisture meter could be considered as an advantage or a disad-vantage, depending on the objectives of the study being performed. It meansthat the readings we obtain represent an average value for a soil layer havinga thickness equal to the diameter of the sphere of influence and varying betweenabout 40 cm and 80 cm depending on the moisture content. This low resolution ofthe equipment is characteristic for the method.

The low resolution makes the use of the depth probe to measure the moisturecontent of the top soil layer rather difficult, as in such a case an appreciableamount of the neutrons escape to the air. However, tho use of a special cali-bration curve to take into consideration the loss of a portion of the neutronsto the measurement or a hemisphere of paraffin, plastic or iron to act as areflector would enable us to start our measurements at a point as close to thesoil surface as 10 to 15 cm.

The low resolution also indicates that thero is no gain in taking measure-ments at depth intervals less than about 20 cm.

VIII. MAIN USES OP THE NEUTRON MOISTURE METER

The depth moisture probe gives directly th?) moisture content per volume andits performance is vory satisfactory especially if we are interested inmeasuring soil moisture changes on the same soil sample, as many possible sourcesof error are avoided in such measurements. Fortunately the changes in soilmoisture content are the most interesting measurements for agricultural studies.The main applications of the neutron moisture meter are:1. Determination of the soil moisture content at a desired depth.2. Through measuring the area limited by the curve of moisture content vs. depth(integration), the quantity of water contained in the soil down to a certain depthcan be calculated.

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3. Determination of the "field-capacity" or water holding capacity afterirrigation or heavy rain.4. If the amount of water contained in the soil as well as the field capacityare known, the amount of irrigation water that should "be applied to bring thesoil moisture content to the field capacity, down to a certain depth, could becalculated.5. Estimation of the adequate irrigation interval under certain conditionsespecially if the wilting point is known? through predicting the time at whichthe moisture content of the soil would approach that corresponding to therecommended moisture level for applying irrigation water.6. Through successive measurements rough but acceptable estimates of waterpercolation and soil permeability "could be made.7. The zone of maximum activity of root systems could be estimated at acertain time as it usually contains less moisture than the surrounding layers.8. Changes of soil moisture distribution or fluctuation of water table levelaround the year could be followed. This provides the information essential foreither improving or planning of drainage systems.9. Studies aiming at investigating the effects of various cultural practicessuch as introducing a fallow period, using wind breaks and mulching on waterconservation or crop water requirements.

IX. PRECAUTIONS WHILE MEASURING(a) Standard reading (in the shield) should be taken at least twice a

day (at the beginning and when half the planned measurements were taken).(b) Compacting the soil around the access tube should be avoided through

the use of a wooden board provided with a hole in which the access tube wouldfit.

(c) A total of about 10,000 counts should be accumulated for eachmeasuring point to reduce and maintain the statistical error at a low level.

(d) The placement of the access tube should be proper and chosen sothat the readings are representative for the area of the plot (effect of littledifferences in soil surface level, canopy shade, dripping of rain water alongthe trunk of a tree, etc.).

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X. REMARKS ON THE USE OP SURFACE PROBES

Surface probes are very valuable tools that are being widely used to testrat'her homogeneous materials where the moisture content is more or less evenlydistributed. This gives such equipment great importance in speeding up moistureand density measurements during constructions of various types such as buildings,roads and airfield runways.

However, the use of surface probes in agricultural studies is not verywidely spread because it is rather easy to take soil samples for moisture ordensity determinations from the top soil layer in addition to the following twomain difficulties:1. The necessity of establishing good contact between the probe and the soilsurface, obliges the investigators to prepare the surface to become flat, smoothand free of plants. This is not always easy to do.2. The moisture content of the top soil layers changes usually very rapidly withincreasing depth. This makes it very difficult to estimate thickness of the soillayer involved in a measurement. In fact the volume of the soil sample involvedin a measurement is variable and increases with the decrease of the moisturecontent or the density.

XI. THE TWO WELLS GAMMA PROBE

Owing to the importance of measuring the distribution of soil moisture in thetop soil layer, a very promising technique has been recently developed for thispurpose. Small access tubes, about 5^ cm long, are placed in the soil, so thatthe distance separating them is fixed and well defined, then a gamma radiationsource is placed in one tube and a detector is lowered to the same depth in theother.

Through using small detector and a collimated (point) radiation source thepathway of the gamma rays could be restricted to a rather thin soil layer of about5 cm height. A portion of the emitted gamma photons is absorbed by the soilsample and the water molecules it contains, while another portion reaches thedetector. The number of gamma photons that reaches the detector decreases as themoisture content of the soil sample increases. If the detector is connected to acounting unit or a rate-meter, the indicated count rate could be transferred toa measure for the moisture content of a certain well defined soil layer with theaid of a calibration chart. Such equipment has been recently developed for labo-ratory as well as lysimeter investigations, and proved to be very promising.

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XIII. BETA GAUGING TECHNIQUE

The dynamic nature of the soil-water-plant systemhas long been recognized.However, measurements of plant water are still absent in most experiments. Oneof the reasons for this is, of course, the difficulty of making such measurements.Recent development of what is called the beta gauge gives promise of removing thisblock. The principle is that, if a suitable radioisotope is placed under a plantleaf, a portion of the radiation therefrom will pass through it and be detectedabove the leaf. The more water in the leaf the thicker it is presumably, and thusless radiation will pass through. While still in the development stage, thisingenious device with improvements should permit continuing measurement of watercontent of a leaf without damaging or destroying it. This technique illustratedin Pig. 6, is likely to become very helpful in the near future in determining theplant need for irrigation thus allowing for applying water at the proper timeintervals so that harmful draught effects could be avoided.

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WATER AND ION MOVEMENT IN SOILS

W.R. Gardner

Water movement in the soil profile influences many important physical andbiological processes related to crop growth. For example, infiltration intothe soil profile and evaporation from the soil surface are determined as much"by soil physical properties and processes as "by atmospheric factors. Theavailability of water for transpiration and growth is often determined by watermovement in the root zcne. Drainage and, hence, aeration of the soil profileare directly dependent upon the water transmitting properties of the soil.

Water moves through the soil in response to the sum of two major forces.The first of these is the force of attraction between the soil particle surfaceand the water molecules. This force, which has been called the matric potential,soil moisture tension, soil suction, or capillary potential causes capillaryrise, water movement to plant roots, and generally, movement from regions ofhigher to lower soil water content. The second water moving force is that ofgravity. Since this force always acts downward it often results in a net down-ward movement of water in unsaturated soil profiles, though the direction ofmotion is determined by the sum of the two forces. In saturated soils, i.e,below the water table, gravity gives rise to the hydrostatic pressure which mayresult in water movement in any direction.

There is now a large body of literature dealing with many different flowproblems. Most solutions of such problems are based upon Darcy's law. Thislaw may be generalized to state that the water flux density is proportional tothe driving force, which is the gradient of the hydraulic head. The hydraulic

• head is the sum of the gravitational head (elevation above the datum plane) andthe pressure or suction head, depending upon whether the soil is saturated orunsaturated. In vector notation this equation is written:

Q - -K grad H (l)where Q is the flux density, H is the head, and K is the hydraulic conductivity.K is a physical parameter characterizing the soil. K is very dependent uponsoil water content, sometimes dependent upon the concentration of ions in thesoil solution and may also vary from point to point in the soil and from seasonto season. When combined with the equation of continuity:

?»/?-t = -div Q (2)where 0 is the volumetric water content of the soil and t is time. JDiuation (l)gives a particle differential equations whose solutions.for appropriate boundaryand initial conditions describe the water content and flux of water at all pointsand times in the system under consideration. These equations represent a verypowerful mathematical tool for the understanding of soil water movement.Obtaining satisfactory solutions of the flow equation can be a very difficulttask. The existence of high speed digital computers, however, now renders possiblesolutions of many problems. Inhomogeneities and large temperature gradientsstill represent formidable obstacles, but otherwise the main task now facing soilphysicists and hydrologists is that of properly defining the boundary conditionsand other field aspects of the problem, including quantitative characterizationof the soil physical properties.

Soils Dept., Univ. of Wisconsin, Madison, Wisconsin. Published by permission ofthe Director of the Wisconsin Agricultural Experiment Station.

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Unfortunately, one cannot ordinarily take a sample of soil from the fieldand analyse it in the laboratory as one does in determining the fertility statusof the soil. For example, one must know not only the soil water content but theenergy (raalric potential) with which the water is retained in the soil. Thesampling process often alters this relationship so that in order to measure thehydraulic head gradient satisfactorily i.n situ methods are necessary. Greatprogress has been made in the past two decades in learning how to solve themathematical problems describing water movement in soils. However, much remainsto be done in the field in order to correctly identify the nature of the problemand characterize the soil. In this regard, our knowledge of soil-water relationsfor arid regions is probably much further advanced than that for humid regionsbecause of the, heretofore, greater necessity for careful water management inarid zones.

Increasingly in the future our need for higher food production will requirebetter management of water regimes in humid regions. This seems particularlytrue for tropical regions such as Southeast Asia where all of the elementsessential for crop production, e.g. radiation, water, C0?, and nutrients arepotentially available year-around, but only by knowledgeable management can thepotential be achieved. An obvious example of the type of problem calling forattention is the management of rice paddy soils so that they need not lie idleduring the "dry" season.

An understanding of water movement in soils is a prerequisite to an under-standing of ion movement. Water movement profoundly influences the direction andrate of ion movement and also may be an important factor in determining 'the ratesof chemical reactions in the soil solution and ion uptake by plant roots. Ionsdo not move any significant distance through the soil unless they are in solution.Dissolved ions tend to move as the soil solution moves. The rate of ion movement,or ion flux density (quantity of ions per unit time crossing a unit cross sectio-nal area), can be described by the equation:

F = Q C (3)where F is the ion flux density, Q is the water flux density and C is the concen-tration of ions in the soil solution. The total flux is obtained by adding upthe individual products of water flux density and concentration over the crosssectional area of interest. Since the flow system in soils is so complex oneordinarily averages the waxer flux and concentration on a macroscopic rather thanmicroscopic scale. Thus, equation (3) is frequently written in terms of theaverage velocity, v, of the soil solution. This velocity is equal to the waterflux dersity divided by the volumetric water content, ©.

Dissolved ions move relative to the soil solution by the process of diffusion,which can be described mathematically:

F = -D 0 grad C (4)where F is now the ion flux density due to diffusion, D is the diffusion coefficient(which is a function of the water content and of soil properties) and C is theaverage concentration of the diffusing ion. The gradient is taken with respect tothe soil solution and not necessarily with respect to the soil matrix. Equations(3) and (4) combine with the equation of continuity to give the particle differen-tial equation (for one dimension):

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5*C = D £2C + > (vC) (5)*t ^X2 ^X

Equation (5), its derivation and solutions are discussed in more detail else-where.

The necessity to average on a macroscopic scale must be taken into accountin the application of equation (5) to transport in the soil. The actualvariation in velocity of the soil solution from point to point throughout thepores results in a process similar in its effect to diffusion and analogous toeddy or turbulent diffusion. This process, called dispersion, is convenientlytreated mathematically to a satisfactory degree of approximation in most soilsystems by replacing the diffusion coefficient D by a dispersion coefficient,here denoted by D. The frame of reference (origin of the x axis in equation (5)is assumed to move with the average velocity v of the soil solution so that (5)reduces to:

"_ (6)4 tMany substances interact strongly with tht* soil profile surfaces, e.g. many

plant nutrients, pesticit3.es, herbicides, and pollutants. The adsorption processreduces distance of movement by both diffusion and mass transport to a similarextent. Only that fraction of a substance in solution moves readily. As arough rule of thumb, one may assume that the distance a substance will moverelative to the distance it would have moved were there no adsorption is in theratio of the fraction of the substance that is in solution. It should be notedthat while adsorption reduces the distance of movement, the presence of adsorbedions results in an increased flux density for a given boundary condition. Thus,more ions are available for uptake from a soil with a high adsorption capacitythan from a soil with a. lower adsorption capacity, given the same concentrationof ions in solution.

If the adsorption isotherm is linear, then:A = R 0 C (7)

where A is the quantity of ions adsorbed per unit volume of soil, and R is theratio of adsorbed ions to ions in solution. The ratio of ions in solution tothe total number of ions is 1/(R + l) = 1/b where b is the notation used byOlsen-3 and several other workers. If the adsorptionisotherm is non-linear, whichis often the case, then R = dA/dC and the equation becomes non-linear. Exchangeions are distributed in a thin layer near the particle surfaces in a non-uniformway that requires special treatment.4

2c.f. Gardner, W.H. 1968. Nutrient transport to plant roots. Trans. 9th Inter.Soil Sci. Cong. Vol. I: 135-141. Adelaide; also references cited therein.Soil Sci. Soc. Amer. Proc. 1962. 26:222-22?.

4Soil Sci. Soc. Amer. Proc. 1966. 30:17-22.

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During ion uptake by plant roots an additional and complicating factor comesinto play. This is the growth and extension of the plant roots through the soil.This growth continuously brings the root into contact with new regions of thesoil and makes more ions accessible for uptake. In a one dimensional system inwhich there is upward movement towards the plant root zone, the maximum rate ofion uptake is eventually determined by the rate of root growth and the rate ofwater movement. This rate is givon by the equation:

P = C (v * ub) a (8)where u is the rate of root growth and v is the velocity of the soil solution.If b = 1 there is no adsorption, in which case root extension and water movementare equivalent in their effect upon ion availability. For b greater than oneroot growth brings the root tip into new regions of the soil from which ions thenmove into the root by diffusion. Both processes are operating together, but itis the rate of root growth and not diffusion which limits the rate of uptake.

In general, mass transport is the only process by which ions can be movedthrough the soil any great distance, that is, more than a few millimeters. Evenover short distances, mass transport will predominate over diffusion if the twoprocesses continue long enough, because decreasing gradients in the case ofdiffusion inevitably lead to decreasing diffusion fluxes.

Many problems remain to be solved relative to ion transport and uptake insoils. The boundary conditions at the site of uptake in the root are difficult .to specify. Many reactions may occur simultaneously at rates that are partiallydetermined by biological activity. But an adequate understanding and descriptionof important soil processes such as nitrate leaching, volatilisation of ammonia,ion uptake, etc. will only come with an adequate understanding of the basicprinciples of water and ion transport. The equations presented here areundoubtedly oversimplified. Only by careful experimentation based upon an under-standing of the present concepts, can they lead to improvements in our descriptionof these important systems.

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THE EFFECT OP ASPHALT BARRIERS ON THE MOISTURE AND NUTRIENTS RETENTIONIN RICE AND SUGARCANTS FIELDS OF SAND SOILSC.C. Wang, K.Y. Li, C.C. Yang, F.W. Ho and'

J.T. WangTaiwan Sugar Experiment Station, Tainan, Taiwan, China

Techniques including the use of radioisotopes have been developed to spraya thin continuous layer of asphalt berrior on the subsurface of sand soil toevaluate its capability of moisture and nutrients retention. This impervioust-o water barrier prevents the water deep penetration and increases the amountof soil moisture and nutrients held in the plant root zone.

Field experiments all indicated that the yields of spring cane andratooned spring cane were greatly increased on the barriers as compared tothat on the controls. Water consumption for spring cane on the barriersshowed only one half the amount used for the controls. No great difference inwater consumption among barriers on cane fields was observed.

Results of first rice crop in 196? indicated that, when the water wassupplied for 12 hrs a day, one-seventh the amount of water was required on theasphalt paddies as compared to that on the controls under the condition ofequal rate of fertilization. The barrier plots surpassed the controls byincreasing the grain yield from 40 - 225$« Under the condition of 24 hrs.irrigation in the second rice crop of 196?, one twelfth the amount of waterand an increase of 40$ of grain on the barrier plots were observed over thecontrols which 36$ more amount of nitrogen than that of barriers was even used.

Laboratory study showed that the barriers have groatly prevented the deeppercolation of water and nitrogen, but not important for phosphorus andpotassium, in the profile of this sand soil. It was found that the optimumdepth at which to place the barrier in this sand soil is 75 era for sugarcaneand 20-30 cm for rice respectively.

With the purpose of efficient use of water and fertilizers on droughtysand soils this technique could be a valuable approach for improving foodproduction.

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THE EFFECT OF ASPHALT BARRIERS ON THS MOISTURE AND NUTRIENTS RETENTIONIN RICE AND SUGARCANE FIELDS OF SAND SOILS

C.C. Wang, K.Y. Li, C.C. Yang, F.W. Ho and J.T. WangTaiwan Sugar Cane Experiment StationTainan, Taiwan, Republic of China

INTRODUCTION

Plants need water and nutriunts for growth. It has been found that'plantroots commonly uptake 500-1500 g of water to synthesize 1 g of organic matter.In fact, the water magazines of a soil, cither from ground water or from irri-gation water actually is the key limiting factor to the growth of plants anddetermines the soil productivity. Deep sand soils usually produce low yieldingof rice and cane* in Taiwan because of thuir low water and nutrition-holdingcapacities. Therefore, it is suggested that if an impervious barrier could beartificially placed in the subsurface of sand soils their water-holding capacityand productivity should be improved.

This principle has been initiated in Michigan, U.S.A. in 1958 when bentoniteclay and plastic films were placed in a Graying sand near Kalkaska. In 1961,they found that using liquid form asphalt instead of bentonite and plasticfilm as a barrier had its advantage of costs and better joint in the seconddirection.

Tests in Michigan in 1966 (l) showed that irrigated asphalt plot producedaround JQffo more vegetables and at least was saving 39 mra of irrigation waterper crop than that without barrier.

As the increase of food production is an integral part of our economicdevelopment, to improve the productivity of low yielding sand soil has becomea. very important problem to be solved in Taiwan.

This study is to investigate the efficient use of water and fertilizer byspraying an asphalt barrier on the subsurface in sand soils and evaluate itseffect on the water properties as well as the optimum depth in which the barrieris to be placed for rice and sugarcane.

EXPERIMENTAL

Rice and cane field experiments were established in February 196? on Fusanfarm of Cheluchen Sugar Mill, Taiwan Sugar Corporation. The soil derived fromsandstone is fine sand all through the profile down to 160 cm. Paddy plotswere 4m x 4ra in size and that for sugarcane, 25m x 8.75n>. Asphalt barrierswere placed 20cm, 30cm, 40cm and 60cm deep for rice plots and 50cm, 75cm and100cm for cane plots respectively. Sugarcane plots included control and dis-turbed control. All plots were hand-excavated and the barrier was hand-sprayedwith grade 50 asphalt in a thickness of 3mm (15 tons/ha).

Available rainfall and total irrigation water applied to the differentplots during the growing season of rice and cane were recorded. Soil moisturecontents were determined, by oven drying, at tensions created as follows:0.1 atmospheres, water pillar regulated its tension with air compressor;

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0.11-1.0 atmospheres, porous plate in a pressure cookerj 1.0-15.0 atmospheres,ceremic pressure plate. Soil nitrogen was analysed by Kjeldahl method. Themovement of phosphorus and potassium in soil profile was measured with radio-isotope technique. A simple and convenient method for measuring nutrientmovement through an undisturbed soil prcfilu has boon designed and may bedescribed as follows:

One hundred ml in size of stainless steel cores wore used to take verticalundisturbed soil samples fron the pDots down to 100cm deep at an interval of5cm. Soil cores were connected first by tape and then fastened with auto-bicycleinner tube to form an undisturbed soil column. Soil mixed with liquid form ofradioisotopes was dried and then placed at the top of this column. Pour thousandthree hundred and twenty milliliters of distilled water which is equivalent to2200mm of total water required for one spring cane crop in this farm was used toleach down automatically through the column. At the top of the radioisotopicsoil layer a constant-head water was always kept in order to make a relativeuniform infiltration. The bottom of the column was supported with filter paperand 360 mesh screen to facilitate its drainage. The radioactivity of filtrationof the column was checked periodically. Soil cores then were untired and driedfor radioactivity determination after the leaching was completed.

RESULTS AND DISCUSSION

The influence of asphalt barrier on crop yieldssa. Rice:

The influence of asphalt barrier on rice yield is shown in Table 2. Alldata indicated that asphalt barriers can be used to improve the rico productionon sand soil. In tho first crop of 1967, rice yield on the barrier plots washighly superior to that on the controls with statistical significance at the 1$level for treatments. But in the second crop of 1967, no statistical significantincrease in rice yield was observed on the barriers as compared to that on thecontrols. This is apparently due to a large amount of water, up to 10837mmwhich was supplied to the controls 24 hours a day to keep those plots floodedduring the whole growing season. Under these favourable water supply conditions,it appears that there was no advantage for the asphalt barrier as far as riceyield was concerned. In the first crop of 1968, the rice on the barrier plotsshowed about 2.5 times as large a yield as the rice on the controls. It was alsohighly significant at the 1$ level for treatments. In the second crop of 1968,the growth of rice on controls was seriously affected by drought at tho time oftwo weeks after transplanting due to the attack of typhoon which damaged theirrigation facilities. The rico on controls was finally killed on October 1968and the yields on barrier plots showed much lower as compared to the previousthree crops. It is obvious that no rice production would be obtained on sandsoil when water supply in the first two weeks after transplanting is limited.

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Table 1 Th* effect of asphalt barriers at various depths on cane yields and water consumption in 19*?/<J8, 1968/69and 1967/1969 crop y«ars

Treatment

ControlEisturb lOOcsa J.-.-?pBarrier 50cra d^pBarrier 75cm cm-?pBarrier lOOoia .j-?rtp

L.S.E. 0.01Availa^. A &jnfa;is i

[967/68 spring cano

icld, t/ha

54.3 .43.983.3

^04.397.1

0.13

water con-sumption, mm

21001950900900

1000

57?cam

1968/69 spring o«nc>ratooned

yi«"ld , t/ha

42.138.949.458.855.3

1.25

wator con-sumption, urn

4234193944*-?398

ll.7i.2nn

1967/1969 24 *onthspring cane

yield, t/ha

70.6•3J.9

103.2.114.7214.4

water con-sumption, mm

252323n9

12941 361139?

1743.2mm

T»ble 2 The effect of asphalt b^•t^i•.*7•3 at various .1-<pth« .in Ho«» ?.n<*. l^tw^ yields and f c i t f i r .-vnaurption in» 1968 r

Treatment

ControlBarri'-r 20cn dcspCarrier 30cts deep?»rri*r 40^m deepBarrier .^Osm dnepBarrier 40c-a ds«p

t.S.D. 0.01

I?o7 rl«* nrcp1st crop

t/hn

0.44*5'4.95.05.64.7

0.43,

w.cor.,mrc2539369359338 .36535«

Available R^infallt 523nn:

?n<^ crop

t^ha3.44.84.64.84.84.8

W.CT..mn10837

625807855840868

240nn {

1968 ric-" cr-*>p1st cropy.t/hn2.35.45.35.55.4%<

0.53

mm14153383144013673*?

2n'i crop

t/h*— .

2.42.02.1

1.92.1

mn45310911511210 \101

460nm

Vtta*. «r.p; 1967/68i y.

l'..518.019.018.418.0^9.4

"•*'?•— . *———• ——

1968/30^?y.t/hn2->.027.832.028.134.<:

31.1

O.S9

w.con.

12!81

••:>•'•13111711?

* Ho d*ta available

b. SugarcaneThe effect of asphalt barrier on spring cane yield is shown in Table 1. In

spring cane of 1967/68, treatment plots surpassed the controls by increasing theyield over 53$ on the 50cm barrier; 92$ on the 75cm barrier and 79$ on the 100cmbarrier respectively. The treatments and controls were statistically signifi-cantly different at 1$ level. In ratooned spring cane of 1968/69, cane yield ofbarriers also showed statistical significance at 1$ level for treatments ascompared to that on the controls. Seventy five cm barriers and disturbed plotsstill performed the highest and lowest yieldings respectively, in this crop year.In 24-month spring cane of 1967/69, 75cm barrier also had the highest yieldingorer the controls. 3y comparing the total yields of spring cane plus ratoonedspring cane with that of 24-month spring cane, we found that the latter had only75$ of the total yields of the former. It seems that it is not preferable togrow 24-month spring cane in Tainan, Taiwan, as far as cane yield was concerned.

The reason that l^cm barrier showed higher cane yield than that on the otherplots will be discussed later. The significant lower yield on the disturbedcontrols as compared to that on the controls could be due to the increase ofcoarser porosity percentage of the soil by disturbing the solum, thus the deepleaohing of soluble nutrients and rapid percolation of water of the profile wereboth increased.

The lower cane yielding on the 50cm barrier as compared to that on the deeperbarriers is apparent due to: 1. the shallower effective soil volume for rootdeveloping. Usually, an 80cm deep solum was found to be the least depth for thebetter growth of sugarcane (3); 2. the lower air porosity of the profile. Aswe calculated, at the depth of 20-4Ccm on the 50cm barrier its air porosity onlyhad 10-0$ by volume (4) when an appreciable quantity of water at low tensionremained above the barrier. It was also found that the critical value of airporosity of the soil was 12-15$ for sugarcane.

Theoretically, cane yield on the 100cm barrier should be the highest amongthe shallower barriers because of its deeper solum and better aeration. Thereason that this was not the case could be due to the fact that the water supplywas not sufficient on the ICCom barriers as shown in the water consumption columnin Table 1. The unfavourable relation between air and moisture in the profilewill also be the reason which will be discussed later.c. Lettuce

Data shown in Table 2 present the effect of asphalt barrier on the yields oftwo lettuce crops. In the second crop of 1968-1969, irrigation water was notgreatly saved but a marked increase in yield was obtained due to the presence ofthe barriers. Statistical analysis showed significance at the 1$ level for treat-ments. Lettuce on the 60cm barrier was superior to that on the shallower barriers,but no great difference in yield was observed among the barrier treatments.The influence of asphalt barrier on the water consumption for rice and sugarcane.

As shown in Table 1 and 2, water consumption for rice and cane was greatlydue to the presence of the barriers. For the first rice crop of 1967,

water consumption on the barriers averaged 368mm as compared to that of 2588mmon the controls. In the second rice crop of 1967, we irrigated the controls 24hours a day for keeping the paddies in a flooded condition and a tremendoussaving of 10,000mm of irrigation water had been found on the barrier plots.

- 187 -

In general, 75-85$ of irrigation water could be saved on the barrier paddies ascompared to those without barrier.

The discrepancy in water consumption for each rice crop was attributed tothe fluctuation of water supply during the growing season.

The dramatic effect of asphalt barrier on the water saving for rice did notoccur on the cane field But it still bore a one-half saving of the amount ofwater for spring cane on th© barrier p .ots whenever the available rainfall wasdeficient. In the ratooned spring ce^c of 1968/69, however, there was almostno difference in water consumption between treatments and controls because thatyear had its advantages in available rainfall.The influence of asphalt barrier on the increasing of water retention capacityof sand soil.

Pig. 1 is the soil moisture tension curve for the subsoil of 20-52cm of thesand soil studied. In order to illustrate the water retention characteristicsof cane barriers, soil moisture contents at various depths were determinedperiodically by oven-dry method. Fig,2 shows the changes in soil moistureduring a short period of growing season after an excessive irrigation on Nov.l6.It was found that soil water at 25cm depth on the controls had dropped to thepoint starting to irrigate at the ninth day and gone down to the wilting pointat the thirty-third day after this flood irrigation. While on the 75cm barrierplots, they, even did not require water until 40 days after that irrigation. Italso means that ono time rf sufficient irrigation on the barrier plots will beavailable for more than 6 weeks as compared to that of 2 weeks without barrierin the dry winter season. Asplu.lt barrier had greatly increased the watesvholdingcapai ity of deep sand soil.The influence of asphalt barrier on the nutrients retention of sand soil.

In addition to the water saving, the effoct of barrier on the nutrientsretention was also evaluated. In paddy field, soil nitrogen is subject to leachovt more easily in deep sand soil than in the finer soils. Soil total nitrogenof the experimental plots after 3 rice crops was analysed and is shown in Pig. 3,The distribution of total ritrogon :".n the profile on the barrier plots wasalways falling in the „•• te of O..C51-0,066$ with only a very small variation.However, the total nitrogen ii the profile 01' the controls decreased witii theincrease of depth and showed three times much more at the topsoil than that atthe ICCcm deep subsoil. Data in Pig. 3 indicated that when the asphalt barrierwas placed in sand soil, the soluble nitrogen would be prevented from leachingin the profile. As the accumulation of soil nitrogen did not occur on the surfaceof the barriers according to the res\ilt of the analysis, we would like to con-sider til at. the present ratw of fertiliser, Ns^Ckt^C = 120 kg/ha, for rice.wasnrt in excess.

Pig, 4 presents the result of the movement of phosphorus and rubidium (insteadof potassium) in the deep sand eoil by using radioisotopic technique, A simplemethod which has been described previously was used to make this determination.Two thousand and two hundred mm of constant-head distilled water which equalsthe maximum quantity of water required for one spring cane crop was leached downthrough the undisturbed isotopic soil column. It was found that the distance ofdownward movement of :-?-32 and Rb-66 only showed 26cm and 18cm from, .the top of thecolumn .respectively.

- 188 -

Potassium is supposed to be leached out easily from the sand soil. But itwas noticed that when a soil has a pH value greater than 6.5 and a high percen-tage of base saturation, potassium mobility is often very low. As'the potassiumfixation capacity would not be high on the relatively aged sand soil studied,the low rate of Hb-86 mobility in this study might be relevant to this explanation.It seems that the presence of barrier at the depth of 50cm or deeper for immobileor relatively immobile nutrients retention on this sand will not be important asfar as phosphorus and potassium (in terms of rubidium) were concerned.Optimum depth and the duration of the asphalt barrier.

After more than two years of study, the optimum depth of the barrier for riceand sugarcane may be discussed as follows:a. For rice:

Since rice is a shallow rooting crop, all measurements indicated that yieldsand water consumption for rice among paddy barriers were not significantly different.Prom the economic point of view, barriers at 20-30cm depth would be preferableto the growth of rice as the barrier is considered by hand spraying.b. For sugarcane:

In or'der to evaluate the optimum depth of barrier for sugarcane, studies inthe field and laboratory had been made simultaneously. Soil moisture contents atvarious tensions were determined and calculated by the methods mentioned above andshown in Table 3 and Fig. 5.

As indicated in Table 3 and Fig. 5, the control only can retain the amount ofwater at the field, capacity through the profile. It was provided with too much airbut less available moisture of only 62mm in depth.

On the 50cm barrier, available moisture increased to the amount of 168mm,2.7'times as much as compared to the control due to the barrier effect. But itsair porosity, on the contrary dropped to 44mm which only can give the upper 15cmlayer of the profile having air percentage greater than 15$ under the condition ofmaximum water-holding capacity. The poor areation occurred in the shallow 15-90cmlayer and is unfavourable to the root developing of sugarcane.

/•

Table 3. Availabfe moisture and air porosity of the sand soil studied at variousdepths of barriers

Depth Available moistureof retained in the.

barriers profile50cm deep

75cm deep100cm deepcontrol*

mm16819621562

index270316346100

Uhsat. gravitationalmoisture in the profile

(air porositv)mm44121

. 208360

index123458100

Depth of upper layerwith air porosityareater than 1 &

15 cm4065100

* Depth of the control was assumed as 100cm deep for calculation.

- 189 -

On the 100cm barrier, both available moisture and air porosity had beenincreased over the control and the shallower barriers. But the high content ofsuch low tension water at 100cm depth was too hard to raise up to the root zonefor young cane. Therefore, when the available moisture in the lower layer hasdropped to the point required to irrigate the water content of the upper 25cmlayer probably has reached its wilting point and the growth of cane must beaffected. On the other hand, it costs one-third more money to place the barrierat 100cm depth than at a depth of 75cm, with only a 9$ return of available moisture.

On the 75cm barrier, a total of 196mm available moisture was conserved inthe profile. It was 3.2'times as much the amount as the control and 17$ morethan that on the 50cm barrier. Within the 75cm deep profile, upper 40cm layer hadprovided with the air percentage greater than 15$ even under the conditions ofmaximum water-holding capacity. In conclusion, the 75cm barrier had provided thebest air and water relations with depth to allow the normal growth of sugarcane.

In addition to the laboratory study, the result of the field experiment alsoindicated that the 75cm barrier plots produced the highest cane yields in twocrop years as presented in Table 1.

The duration of the barrier is still under evaluation up to the date of 'report. No serious defect of barriers has been observed. In Michigan, U.S.A.(2), they estimated the duration of asphalt barrier with 15 years.Economic evaluation of asphalt barrier.

The most important thing people are interested in in this experiment mustbe how long this investment takes until it pays back. The cost for installingthe barrier by hand was too high to be considered for oxter*-, on. An asphalt appli-cator developed by the International Harvest Co. has been demonstrated.in March,1969 in the States. They estimated that if tht; barrier can be installed by anapplicator, the total cost should be around U.S.$ 620.00/ha in the United States.

According to this study, the 75cm barrier averaged 60$ increase in yieldingover the control for spring cane and does not consider the advantage of watersaving, an additional 30 tons/ha (a very conservative estimate) of cane, or 3.6tens of sugar should be produced per year and cost U.S.$ 216.00 (on the basis ofa sugar price of U.S.$ 60.00/ton). Therefore, as the barrier can be installed bymachine the reasonable time for getting money back by growing sugarcane will be3 years.

As for rice, if equal amounts of water were used on the barrier and the control,it seems that no production will be obtained on the latter. According to thedata of the second rice crop of 1967 $ at least a 40$ increase in yielding wouldbe maintained on the barrier over the control in spite of the tremondous saving ofirrigation water. The local price for rice is U.S.ft 115/ton. Thus, as a veryconservative estimate, 2.8 tons/ha (two crops) more rice will be produced everyyear on the barrier as compared to the control, and cost U.S.8 322.00 per year.It appears that this investment can be paid for within two years when the barrieris placed by applicator. ....

Of course, the cost of the applicator must be taken into consideration.

- 190 -

ACKNOWLEDGEMENTS

The authors wish to express their sincere appreciation to Dr. R.L. Cook andDr. A.E. Erickson of Michigan State University, U.S.A.; Mr. L.C. Hsi of JCEE,Bepublic of China; Dr. K.C. Liu and their colleagues of Taiwan Sugar ExperimentStation for their technical and financial assistance in preparing this experiment.

REFERENCE

1. ERICKSON, A.E., HANS1N, C.M. and SMUCKER, A.J.M. The Influence of SubsurfaceAsphalt Barriers on the Water Properties and the Productivity of Sand Soils.Trans.Int.Gong.Soil Sci. £ 1 (1968).

2. ERICKSON, A.E., HAWSES, C.M., SMUCKER, A.J.M., LI, K.Y., HSI, L.C., WANG, T.S.and COOK, R.L.

Subsurface Asphalt Barrier for the Improvement of Sugarcane Production andthe Conservation of Water on Sand Soil. Proc. ISSCT j3 (1968).

3. SHIH, S.C., LEE, L.S., PERNO, L.S. and UWG, T.An Investigation on Root System of Sugarcane. Rept. TSES, I2s$2-49 (1954).

4. YANG, C.C.The Theory and Practice on the Use of Asphalt Barrier to Improve the Water-Holding Capacity of Sand Soil. (Unpublished).

- 191 -

Field capacity

Fig. 1

i c r- '.K> ')6Moisture content, by volume

Soil moisture curve for 20-52 cm deep horizon

-'•8

5k,

35

»O

\ at y> cm deep

!^ !-

W P* * '"•"

barrier, 75 enbarrier,100 en

50 en

disturb 100 encontrol

Soil

Moi

sture

:>!> -

1.5

1O

( Date of excessive irrigation: 11/16 )

at ?5 en deep

,,i :/•.*. i.V « './U

barrier, 75 enbarrier, 100 onbarrier, 50 ondisturb, 100 encontrol

i V • >Pijr. 2 Effect of asphalt barriers on the soil moisture

retention of sand soil on sugarcane field- 191 b -

Fig* 3 Variation of total nitrogen contents of theasphalt paddies as a function of depth dueto the presence of barriers

_0._Qf />/: 0.0 rj O.Gfr 0.03 0.02 $ N

Ku50

60

70

80

90

control

barrier,60cm d«up

—.*-.._ barrier.

—-*—*—.barri.or,^0cm deep,(Urea)

—*—•—barrier130cm cloep

barrier ,2Ocin deep

- 191c -

o<3<Mj-

f-lT*O

h<H

b.3

10

30-

50-1

activit Les ojf P_32 and Rb-86 in a leachedundisturbed soil colunu ( cprn/g dry wt. )_logo___1590

P-32 Rb-86

Distribution curves of P-32 and Rb-86 in an undisturbed soilcolumn aftur loaoiiin^ with 2200nm of distilled water

Ft ;.5 '•>«••-*• «•-•control

.a... .porosity %ft . '•'••> ..>'i',..?P._. 1C' 0w r. .—•!'•;. •...•« . • .,• -"."V":••• 5«•:{«'« :-.:v«.'- /v.'.•.:•;;/«

10:• '=:• : ! . • • ! • ' • : • • ' . a'!•••:• ;x'•-.:!,'... .. '••' ••• .*<,:•{: "' ' -vi.*•}*. ' '• •* * ** I

* *;. * * * . . . * • • . • • » »20 :; • ; ... . .. • -'ii

30 .'.

*oi':"-":!ii:':"\? •• . , . . --•'W. •-..:•:•• ;"v:.:^--. iihr'-.-..)'-; .. •: :•' ••'.'-...„'

w.|:.r

100 o%

."v-.~i r-*--''":''-' '•*^« _ * ' * * • • **,••••

»•/. '!•/-•• " -.T v."..;.' v • .-.:« * :. •• •>• . ; .» . . .• .. •. •

•r rclti* i^n* :>f s>aiidbarrier,jOcro

t » i r porosity jti . f%.JOJ)|

and without Oorri't«r«bar.ri*'xv/5<3n

.air ??o10 JO __ JO C

".*•»? .. .It.. ..I. .

r-Mi^V :;:v:-5>'-ijr.' ji;1'.;':';> •.*••'•"••;'.:!i/;Hv ••' • •• .'• '••'.'*x.'' " " i !'• . :•::«-. '> rr-x •. • •:

&2%zz&&>••?''>*•-tezZ^^

air p.>rosilygravi la ti onul »*ator4avilaoio nuibturehygroscopic water

barrier, lOCciuporosity f&

?3Oist.urc,^oy volume noi3turof%by

RECOMMENDATIONS

The Group noted that its terms of reference were the use of isotopes andradiation in soils, fertilizer and water studies. In considering its recommen-dations the Group particularly recalled two of the Food and Agriculture Organi-zation's current priority areas, namely, high yielding varieties and increasingprotein production.

Further, considering the importance of ric-e as the major crop of the Region,special note was taken of the recommendations of the llth Session of the Inter-national Rice Commission Working Party on Soils, Water and Fertility Practicesand their endorsement "by the Ccmmissior. at itc 11/6C meeting in Tokyo.

The Group recommends that:RICE1. The existing results for P and K fertiliser placement and timing, attainedwith labelled fertilizers, should be confirmed an far ar necessary for the newhigh yielding varieties. In this context a limited number of studies usingisotope techniques to study and compare the root distribution of the new varietiesare also desirable.2. Further work is required on the time of top dressing of nitrogen fertilizer,asing N-15» and the determination of the particular place in the plant where thefertilizer is utilized. (IRC Working Party Recommendation 5).3. Further work be initiated in comparing the efficiency of different naturalphosphate sources. Recognizing that an initial screening can be carried out inpot experiments by a modified 'A-value' technique, it is suggested that the JointFAO/IAEA Division might assemble a collection of natural phosphate sourcesifordistribution to Member States who wish to carry out auch.-^omparative isotope testson their own soil types (IPO Working Party Recommendation 4),4. That N-15 studies be made of the effect of mid--term drainage (Nakabashi) andintermittent irrigation on the efficiency of N-fertilizer utilization^ For thoselaboratories with the necessary facilities and personnel, associated studies onN-conversion, N-fixation and loss, and nitrogen fixing nicro-organisms aredesirable.OTHER CROPS5. The Group, although noting that rice is the moat "significant crop in theregion, recommended that increased interest and effort must be devoted to otherimportant economic crops, such as legumes, sugar cane, oil seed and fibre crops.Optimum fertilizer and water management practices for these crops are based on veryuncertain guidelines. It was further noted, that with the increased emphasis beingdevoted to better land utilization through the use of earlier maturing cropsgrown in sequence, that fertilizer management practices for each successive croprequire attention.

192 -

SOIL CHEMISTRY AMP RELATED STUDIES6. The Group strongly recommends that individual institutes within the regioncontinue to expand research using isotopes and radiation in soil-plant nutritionstudies, and noted the following subject matter areas; kinetic studies ofnutrient movement in soils; turnover of organic matter; the nitrogen cycle inpaddy and upland soils; and micro nutrient investigations.

WATER ' . '. '7. The Group recognized that water has a profound influence on all physical,biological and chemical reactions influencing the soil-plant system and notedthat the Agency has a real and central role to play in water efficiency andmanagement studies using isotopes and radiation techniques in the region.Within this general context, and having noted the serious shortage of trainedpersonnel the following in order of priority, were recommended.8. That the water management practices and associated soil moisture budget,together with accurate measurements of the environment be recorded for currentand future experiments where labelled fertilizers are used.9. The neutron moisture meter (depth probe) has proven to be a very usefultool for routine measurements of soil-moisture profiles and its extended use inirrigation and soil moisture studies should be encouraged.10. In order to draw attention to the potential significant applications ofisotope and radiation techniques in soil water movement and efficiency studies,exchange of information and training of scientists should be encouraged in theregion.ORQANIZATIOtt11. Recalling the success of the co-ordinated approach as adopted in the Six-Year Rice Fertilization Study with Isotopically Labelled Fertilizers, the Grouprecommends that wherever possible this approach be continued. It was felt thatwhen a number of laboratories in different countries work on the same topic,more authoritative results are achieved. It is recognized, however, that thisapproach is not always possible when very specialized equipment and expertiseis required.FUNDING12. Recalling the continual need for funds to carry out work on the subjectswhich have been recommended, and recognizing the limited financial capacity ofthe IAEA research contract programme, the Group requests the Joint FAO/IAEADivision ±o continue efforts to obtain support for work in the Region concernedwith the use of isotope and radiation in soils, water and fertilizer studies.

- 193 -

LIST OF PARTICIPANTS

NAMEABDULLAH, Nazir

ANANTAKUL, Jarusari

BAJARD, Ch. J.L.BARRADA, Y.

BOONNITTEE, A.

CHOLIKUL, Wisit

CRAWPOHD, R.

DASANANDA, Sala

DATTA, N.P.

DEWIS, J.W.

PREDRIKSSON, L.

GARDNER, W.R.

KHAN, A.B.

LAMPOWPONG, Somboon

INSTITUTIONBadan Tenaga Atom Nasional Djl.

Palatehan1/26 Block K.V. Kebajura BaruDjakarta, IndonesiaSoil Conservation DivisionDepartment of Land DevelopmentMinistry of National DevelopmentThailandFAO, Bangkok, ThailandJoint FAO/IAEA DivisionKSrntnerring 11A-1010 Vienna, AustriaFaculty of Science and ArtKasetsart UniversityThailandTechnical Division, Rice DepartmentMinistry of AgricultureThailandRegional Development OfficeAmerican EmbassyBangkok, ThailandDirector General, Rice DepartmentMinistry of AgricultureBangkok, ThailandI.A.R.I.New Delhi-12, IndiaFAOBangkok, ThailandUnited Nations21, Curzon RoadNew Delhi, IndiaSoils DepartmentUniversity of WisconsinMadison, Wisconsin 53706, U.S.A.Atomic Energy CentrePrincipal Scientific OfficerP.O. Box 164Ramna, Dacca-12, PakistanTechnical DivisionRice DepartmentMinistry of AgricultureBangkok, Thailand

- 194 -

LEGO, J.O.

MISTRY, J.B.

MtTKERJEE, H.N.

NAKOENTHAP, Art

NILUBOL, M.L. Anong

NISHIGAKI, AkiraNISHIQAKI, Susumu

PAMORNCHAN, Boonsom

PATTERSONPUH, Y.S.RATISUNTHORN, Paderm

RICE, 0.

SANITWONOSE, Patoom

SHIEH, Yuh-Jang

SHIM, Sang Chil

SUWANAWONG, Sombhot

Plant Industry StationBeltsville, Md. 20?05, U.S.A.Biology DivisionBhabha Atomic Research CentreTrombay, Bombay-74, IndiaPADBangkok, ThailandAtomic Energy LaboratoryKasetsart UniversityThailandOffice of the Atomic Energy for PeaceMinistry of National DevelopmentBangkhen, ThailandJapanSoil Fertility DivisionDepartment of Soils and FertilizersNational Institute of Agricultural

SciencesNishigahara, Kitaku, Tokyo, JapanSoil Conservation DivisionDepartment of Land DevelopmentMinistry of National DevelopmentThailandUSOM, Bangkok, ThailandFAO, Bangkok, ThailandFaculty of Science and ArtKasetsart UniversityThailand642, Petchburi Road,U.S. Operations MissionsAID RepresentativeBangkok, ThailandTechnical Division, Rice DepartmentMinistry of AgricultureBangkok, ThailandInstitute of BotanyAcademia SinicaNankang, Taipei, Taiwan, Rep. of China46-305, Whagok-Dong, Yungdongpo-KuSeoul, KoreaTechnical Division, Rice DepartmentMinistry of AgricultureBangkok, Thailand

- 195 -

TAOBASHI, J.

THENABADU, M.W.

VAIT'T VOUDT, B.D,

VOSE, P.B.

WANT, Chwan-chau

YINaCHON, Yubol

SCIENTIFIC SECRETARY

Rennie, D.A*

FAO, Bangkok, ThailandDivision of Agricultural 8hemistryCentral Agricultural Researcn InstituteGannoruwa, Peradeniya, CeylonFAO, Bangkok, Thailand94, Bluehouse LaneOxted, U.K.Taiwan Sugar Experiment StationTainan, Taiwan, Rep. of ChinaSoil Fertility SectionAgricultural Chemistry DivisionDepartment of AgricultureThailand

Joint FAO/IAEA DivisionInternational Atomic Energy AgencyVienna, Austria

- 196 -