FIRST RESEARCH CO-ORDINATION MEETING OF THE

FAO/IAEA CO-ORDINATED RESEARCH PROGRAMME

ON

THE USE OF ISOTOPE TECHNIQUES IN STUDIES ON THE

MANAGEMENT OF ORGANIC MATTER AND NUTRIENT

TURNOVER FOR INCREASED, SUSTAINABLE AGRICULTURAL

PRODUCTION AND ENVIRONMENTAL PRESERVATION

(D1-40.08)

___________________________________________________________

INTRODUCTION TO THE PROGRAMME

AND

EXPERIMENTAL GUIDELINES

______________________________________________________________

7 - 11 OCTOBER, 1996 VIENNA INTERNATIONAL CENTRE

VIENNA, AUSTRIA

CHRIS VAN KESSEL SCIENTIFIC SECRETARY

CONTENTS Page 1. Introduction 1 2. The Co-ordinated Research Programme 3 3. Objectives of the First Research Co-ordination Meeting 3 4. Programme 4 5. Opening Remarks 8 6. Abstracts of Presentations 11 7. Experimental Co-ordination 17

Experiment A

Main objective 17

Experimental protocol 17

Step 1 Selection 17

Step 2 Measurements 18

Step 3 Labelling with 15N 19

Step 4 Sampling 20

Optional additions 22

Experiment B

Main objective 22

Experimental protocol 23

Treatments 23

Sampling 23

Experiment C

Main objective 24

Experimental protocol 24

General Comment 25

8. Suggested References 26

Annex 1 Sampling instructions 28

Annex 2 List of participants 20

Annex 3 Figures 34

1. Introduction In the developed and developing worlds, there is renewed interest in the application of organic amendments to soil, as a means of improving its quality and thus sustaining its fertility and productiveness. In the developed world, the health of soil is being stressed by over-fertilization. During the past 50 years, inorganic fertilizers have largely replaced organic amendments, and with modern tillage practices the soil's organic matter content has been declining. Large-scale efforts are now underway to reduce tillage and adopt crop-residue practices that will improve soil quality. In less-developed countries, intense and prolonged use of the soils have had similar effects: reduced soil quality causing decline in crop production; again, organic amendments can reverse the deterioration. Locally-available organic residues can be used in conjunction with inorganic fertilizers, and, when harmony is achieved, the efficiency of use of added nutrients and those already present can be enhanced. A Consultants Meeting on the Use of Isotopes in Studies on Soil Organic Matter was convened in Vienna, 4-7 September 1995. The main objectives of this meeting were (i) to review the state-of-the-art on soil organic matter studies, (ii) to discuss how the decomposition of soil organic matter in tropical soils affects nutrient release and soil physical/chemical properties, (iii) to determine the factors that control nutrient losses from decomposing organic matter, and search for management options to increase the use efficiency of the released nutrients by the crop, and (iv) to examine how computer-simulation models can play a role in predicting optimal organic matter levels. The recommendation from the Consultants Meeting was to initiate a Co-ordinated Research Programme (CRP) on increasing crop production through the management of soil organic matter and nutrient input. Based on this recommendation, the Joint FAO/IAEA Division, through the Soil and Water Management & Crop Nutrition Section initiated a CRP on soil organic matter and nutrient cycling with twelve Research Contract Holders and 3 Agreement Holders. The overall objective of this Co-ordinated Research Programme is: To increase or sustain crop production through management of

soil organic matter and nutrient input.

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2. The Co-ordinated Research Programme The CRP on "The Use of Isotope Techniques in Studies on the Management of Organic Matter and Nutrient Turnover for Increased, Sustained Agricultural Production and Environmental Preservation" consists at the present time of 12 contract and 3 agreement holders. Participants were selected from approximately 50 who submitted proposals. The selection of the 12 contract holders was based on the scientific merit of the proposed work, the scientific background of the applicant, and geographical location. Proposals from contract holders are still being submitted (October 1996), but, with the 12 selected contract holders in place, no new proposals can be funded. This CRP will last for 5 years and Research Co-ordination Meetings (RCMs) will be held every 15 to 18 months, for discussion of objectives among Contract and Agreement Holders, and members of FAO/IAEA and other Institutes. RCMs also provide a forum for discussing research results and possible improvements in the research protocols. 3. Objectives of the First Research Co-ordination Meeting The objectives of the RCM were: (i) To provide an opportunity for participants to get acquainted and become familiar with the research programmes of their fellow Contract and Agreement

Holders on soil organic matter and nutrient cycling. (ii) To discuss the merits of the objectives of the CRP. (iii) To establish a protocol for experiments to be conducted by the participants within

the framework of the CRP.

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4. Programme Monday, 7 October 09:15 Official Opening J. D. Dargie Director Joint FAO/IAEA Division C. Hera Head, Soil and Water Management & Crop Production Section 09.45 Remarks by the Scientific Secretary 10.00-10.30 Coffee Break Session I Chairperson: C. Hera 10.30 - 11.00 S.M. Rahman Bangladesh "Organic matter management for increased and sustainable agricultural production in Bangladesh" 11.00 - 11.30 K. Reichardt Brazil "Geostatistical studies applied to Amazonian soils: organic matter related properties in a forest-pasture succession" 11.30 - 12.00 E. Zagal Chile "Decomposition of 15N and 14C-labelled residues in volcanic soils of the Chilean Central Plain" 12.00 - 13.30 Lunch break Session II Chairperson: S.K.A. Danso 13.30 - 14.00 J.Y. Wang P.R. China "Isotope tracer study on the long-term change and balance of soil organic matter in Chinese paddy soils and British arable soils" 14.00 - 14.30 P.T. Cong Viet Nam "The use of isotope techniques in studies on the management of organic matter for sustainable agricultural production in South Vietnam"

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14.30 - 15.00 M.S.A. Safwat Egypt "Studying the effect of organic matter, water management and inoculation on nutrient turnover and biological nitrogen fixation of certain plants using isotope techniques" 15.00 - 15.30 Coffee Break 15.30 - 16.00 R. Abu Bakar Malaysia "Utilization of organic fertilizers and crop residue for sustainable maize production and effects on soil organic matter" 16.00 - 16.30 J.Z. Castellanos Mexico "Soil organic carbon and nitrogen cycling under different crop rotations and tillage practices in an irrigated vertisol in Central Mexico" 16.30 - 17.00 D. Amara SierraLeone "Studies on organic matter turnover and build-up in ultisols and oxisols in Sierra Leone" 17.00 - 17.30 R. Sangakkara Sri Lanka "Management of soil organic matter to enhance soil productivity and sustainability in Sri Lanka" 18.00 Reception Tuesday, 8 October Session III Chairperson: D. Powlson 09.00 - 09.30 S.K.A. Danso Ghana "The contribution of legume/cereal crop residues to soil organic matter and fertility" 09.30 - 10.00 N. Sanginga Nigeria (title not available) 10.00 - 10.30 D. Powlson U.K. "The influence of straw incorporation and soil type on nitrogen losses" 10.30 - 11.00 Coffee Break

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11.00 - 12.00 C. van Kessel IAEA "Use of C isotopes in nutrient cycling studies" 12.00 - 13.30 Lunch Break Session IV Chairperson: F. Zapata 14.00 - 15.00 D. Powlson U.K. "C budgets in agro-ecosystems: a modeling approach" 15.00 - 16.00 C. van Kessel IAEA "Principles of the A value: questions and some answers" 16.00 - 16.30 Coffee Break 16.30 - 17.30 K. Reichardt Brazil "Agronomic research: from small plot to farmer's fields" Wednesday, 9 October Session V Chairperson: K. Reichardt 09.00 - 09.30 I. Mohamed Morocco (title not available) 09.30 - 10.30 Zaharah Abdul Rahman IAEA "Assessing the N contribution from residues: the direct versus the indirect approach" 10.30 - 11.00 Coffee Break 11.30 Departure for Seibersdorf 13.00 - 16.00 Visit to Seibersdorf Laboratories Thursday, 10 October Session VI Chairperson: N. Sanginga 09.00 - 10.30 Discussion on the experimental protocol 10.30 - 11.00 Coffee Break 11.00 - 12.30 Discussion on the experimental protocol and implementation 12.30 - 14.00 Lunch Break

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14.00 - 15.30 Preparation of experimental guidelines 15.30 - 16.00 Coffee Break 16.00 - 17.30 Preparation of experimental guidelines Friday, 11 October Session VII Chairperson: N. Sanginga 09.00 - 09.30 Presentation of experimental guidelines 09.30 - 11.00 Final discussions on experimental guidelines 11.00 - 11.30 Coffee Break Chairperson: Chris van Kessel 11.30 - 12.00 Closing Session 12.00 - 13.30 Lunch 13.30 - 15.30 Individual discussions

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5. Opening Remarks by Mr. J.D. Dargie, Director of the Joint FAO/IAEA Division. On behalf of the Directors General of the Food and Agricultural Organization of the United Nations and the International Atomic Energy Agency, I would like to welcome you to the first Research Co-ordination Meeting on the use of isotope techniques in studies on the management of organic matter and nutrient turnover for increased, sustainable agricultural production and environmental preservation. As a general comment, the research carried out by a CRP should follow an holistic approach, be problem-driven not technique-driven, and should encompass strategic, applied, and adaptive components. Furthermore, the results gathered should reflect an international perspective in order to achieve maximum, world-wide 'spill-over'. Therefore, the main objective of a CRP must be clearly defined, and followed by sub-objectives that can be met. As such, more-modest sub-objectives are preferable to a series of ambiguous objectives that have a low likelihood of fulfillment. In developed countries, food is being produced by an ever-decreasing number of farmers. New technologies are constantly being devised and adopted, better seed varieties introduced, and new management practices promoted. The computer is becoming an essential tool for farmers, and it is apparent that its use will increase dramatically in the future. However, these improvements in food production in the developed world are not without negative repercussions. High production goes hand in hand with high input of nutrients and other resources, and increased inputs of fertilizers and pesticides have led to intense pressures on the quality of the soil, the environment, and hence on society as a whole. As a reaction to this, numerous efforts are under way to reduce inputs and reach a new balance that can be sustained. The role of organic amendments as nutrient sources is receiving more attention as considerations of the long-term health of the soil becomes part of the decision-making process on how to manage the land. A rather different situation prevails in many less-developed countries where per-capita food production has been on a steady decline, and increases in population are not in synchrony with concurrent increases in food production. Soils in many of those countries have low inherent fertility, are old and highly weathered, and have lost their capacity to retain and exchange nutrients. And the situation is often exacerbated by pest problems and severe weather conditions. Soil productivity, however, can be enhanced with fertilizers and by addition of organic materials, and although the use of fertilizers alone can enhance crop yields, it is likely that a combination of inorganic and organic amendments will be needed to achieve sustainable food production. A wide variety of farming systems exist in tropical countries, each with its own characteristics and adaptations to the local environment. Many of these cropping systems, developed over centuries, were rather efficient in nutrient use, and were able to sustain food production. When a piece of land lost productivity, it was put to rest - left in fallow - until it had recovered and could be planted again. Some of the nutrients removed from the field were returned, for example as manure, and with the inclusion of the fallow period the output of nutrients was close to the input. Such systems were sustainable as long as the fallow period was sufficiently long to ensure adequate input of nutrients. However, increases in population are forcing shorter periods of fallow, hence the soil does not fully recuperate and cannot achieve prior yield potential. With the cycle of sustainability disrupted, new avenues have to be found, not only to regain sustainability to produce food, but also to increase production in order to feed the ever-increasing population. Management options must include both organic and inorganic additions to improve the fertility status of the soil. Furthermore, integrated system-approaches should be adopted to increase the use efficiency of the available nutrients, thereby reducing unwanted losses. A key aspect of the achievement of long-term sustainability is the improvement of nutrient-use efficiency, which should not be considered in terms of a particular crop but rather in terms of

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the cropping system as a whole. The sustainability of a cropping system is determined largely by its losses: if it receives 100 kg N ha-1, can it retain that N within its borders or will a significant fraction be lost through leaching, run-off, or gaseous conversion? To increase the yield of a cropping system, nutrients are often added. For a soil to be able to capture, store and recycle those nutrients, the presence of soil organic matter is of paramount importance. Soil organic matter is a prerequisite of life on earth. It serves as a temporary storage place of energy and nutrients. When the stored energy is used by soil micro-organisms, released nutrients become available for plant growth. Without organic matter and the microorganisms that feed on it, the flow of nutrients between the atmosphere and pedosphere would come to a halt, and life on earth would cease. And soil organic matter has other roles to play. It enhances the stability of the soil, increases aeration and capacity to hold water, and improves structure, which minimizes erosion and ameliorates the environment for plant-root development. Therefore, an improvement in the quality of a soil is often related to an increase in organic matter content obtained through addition of organic residues and management practices that control the rate of decomposition. On decomposing, the organic amendment releases nutrients, and, ideally, that release should be synchronized with the nutrient demand of the crop. Such synchronization between supply and demand improves the efficiency of use of the available nutrients. There has been a tremendous increase in the use of stable and radioactive isotopes in residue-management and nutrient-cycling studies. Our knowledge of nutrient cycling and soil organic matter dynamics in agro-ecosystems would be greatly limited without the use of isotopes. They allow the researcher not only to determine the flow of a nutrient in a cropping system, but also its fate. Detailed understanding of the processes that control nutrient flow between the various sources and sinks, and sinks that become sources again, can be obtained only with tracers such as 14C, 13C, 15N and 32P. Organic matter studies, however, should not solely be focussed on the capacity of organic amendments to release nutrients to the crop. Other questions should be asked: - Does the addition of organic residues lead only to an increase in the yield of the targeted

crop or does it improve the performance of the entire crop rotation? - How do organic amendments contribute, directly and indirectly, to increases in yield, and

how should those contributions be measured? - Does increase in release of nutrients from organic amendments also add to increase in

nutrient loss, and, if so, what management practices can be adopted reduce such loss? - Should nutrient-use efficiency from an organic amendment be based on recovery by the

crop to which it is applied, or rather should we evaluate the effectiveness of the system as a whole to retain nutrients?

- Where should field research be carried out: under controlled conditions on experimental stations or on fields that realistically reflect the conditions with which the local farmer is confronted?

- And as a final question, should this programme on soil organic matter look only at nutrient cycling, or is it possible for some of you to become a part of a larger research team that will investigate the various components of a cropping system of which soil organic matter is just one?

To answer some of these, and to predict changes in nutrient availability with a new management practice or with a new organic amendment, simulation models will be essential. Finally, I hope that you will enjoy this first RCM on soil organic matter. Time permitting, I also hope that you will be able to see something of beautiful Vienna, in particular those of you who are here for the first time. Once again, I welcome you to the Vienna International Center and hope you have a pleasant and fruitful meeting.

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Mr. C. Hera, Head of the Soil and Water Management & Crop Production Section explained that the CRP on soil organic matter was proposed some years before and that initial work was carried out by M. P. Salema and S.K.A. Danso. A Consultants� Meeting was held a year ago and the report from that meeting was distributed to all participants. Mr. C. van Kessel, Scientific Secretary, stressed that FAO/IAEA is not a granting agency but rather acts as a facilitator for researchers in different countries with common interests. Funding from the Agency should therefore be used as seed money by the participants as leverage for additional funding from granting agencies.

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6. Abstracts of Presentations UTILIZATION OF ORGANIC FERTILIZERS AND CROP RESIDUE FOR SUSTAINABLE MAIZE PRODUCTION AND EFFECTS ON SOIL ORGANIC MATTER. A.B. Rosenani, A.R. Zaharah, S.D. Zauyah Department of Soil Science, Faculty of Agriculture, Universiti Pertanian Malaysia, 43400 Serdang, Selangor, MALAYSIA Malaysian highly weathered acid soils are low in soil organic matter and cation exchange capacity (CEC). Thus, in recent years, organic materials, as a source of nutrients and soil amendments (in combination with chemical fertilizers), have been recommended together with crop residue incorporation. Palm oil mill effluent (POME) is one of the major waste products of the palm-oil industry, and is a threat to the environment. However, due to its high nutrient content, POME can be used an organic fertilizer, and is now recommended for use in field crop cultivation, such as maize and groundnut. Another important organic fertilizer in Malaysia is poultry waste (chicken dung), commonly used by vegetable farmers. As it is easily and abundantly available, it is also recommended for other crops, including maize. Several studies had been conducted to show the beneficial effects of POME and chicken dung on crops. But these studies merely give yield performance data and effects on soil parameters to indicate improvement in soil fertility. There is poor understanding of the organic matter turnover in our highly weathered acid soils. In order to manage organic matter application to crops more efficiently, we need to know more about the dynamics of the soil organic matter in these soils by quantifying some of the related soil and plant parameters. Therefore, this proposed project using isotope techniques is important. The project protocol involves the following treatments (i) POME + gliricidia + 50% recommended (rec.) N rate, (ii) POME - gliricidia + 50% rec. N rate, (iii) Chicken dung and paddy straw mixture + 50% rec N rate, (iv) Chicken dung + 50% rec. N rate and (v) 100% rec. rate chemical N fertilizer. Each treatment (replicated 4 times) will consists of subplots, with or without crop residue incorporation, and microplots for 15N-labelling. Maize will be planted in rotation with groundnut. All treatment plots will be limed and receive recommended rates of P and K fertilizers. ISOTOPE TRACER STUDY ON THE LONG-TERM CHANGE AND BALANCE OF SOIL ORGANIC MATTER IN CHINESE PADDY SOILS AND BRITISH ARABLE SOILS Jia Yu Wang, Institute of Soils and Fertilizers, Zhejiang Academy of Agricultural Sciences, Hangzhou 310021, P.R. CHINA The general target of this research is to understand the mechanisms that govern the differences in soil organic matter (OM) dynamics among the different climatic and soil conditions. To monitor long-term changes of soil OM under different climatic conditions and soil types as well as cropping systems, isotope tracers and long-term experimentation will be utilized. Ultimately, new recommendations for soil OM management will assist in attaining sustainable soil fertility and crop production.

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THE INFLUENCE OF STRAW INCORPORATION AND SOIL TYPE ON NITROGEN LOSSES. P.R. Poulton, I. Craciun, D.S. Powlson and D.S. Jenkinson IACR-Rothamsted Harpenden, Herts., UK. The incorporation into soil of cereal straw having a wide C-to-N ratio (typically about 80) can cause immobilization of inorganic N as the soil microbial biomass proliferates. In the past this has been regarded as a potential problem as immobilization would decrease the amount of N available for the subsequent crop. However, many arable soils in north-west Europe contain an excess of nitrate in the autumn which contributes to nitrate leaching during winter. Straw incorporation is now seen as a means of decreasing the amount of nitrate at risk to leaching. An experiment was conducted at 3 sites, having clay contents of 14, 26 and 39%. The soil nitrate pool was labelled by application, in September, of either 2.5 kg N ha-1 as K15NO3 at 81 atom % excess or 50 kg N ha-1 as K15NO3 at 4.6 atom % excess. The treatments were applied to areas where wheat straw had either been burned or was immediately ploughed in. The next wheat crop was sown shortly afterwards. Visual assessments were made of the extent of soil movement and the position of the plot (each 2 x 2 m in triplicate) were moved accordingly. This was later checked by analyzing each wheat row individually for 15N. Soil and crop samples were taken from the central area of each plot in the following April or May. Where the very small quantity of 15N had been applied (2.5 kg N ha-1) the proportion retained in soil, through immobilization or uptake into plant roots, was greater than for the larger application (50 kg N ha-1) in the sandy and silty soils. This trend was less clear in the clay soil. For the small application it ranged from about 20% in the sandy soil to 60% in the clay soil. The corresponding values for the larger application were 5-15% in the sandy soil to 35-60% in the clay soil. Incorporation of straw generally increased retention of 15N in soil. In the sandy soil retention increased from 4% to 16% for the larger 15N application; the corresponding values for the silty and clay soils were 14% to 41% and 34% to 61%, respectively. In the silt and clay soils the increased retention of 15N in soil was reflected by decreased uptake in the crop. This was not so in the sandy soil, perhaps because of turnover of organic N is faster in a sandy soil due to less clay protection of microbial metabolites. In two soils the incorporation of straw decreased the total loss of 15N from the crop/soil system, but the difference was probably significant only in the sandy soil: a decrease of 82% to 72%. The overall impact of straw incorporation on nitrate leaching would appear to be small. In the long term, continued incorporation of straw will lead to an increased quantity of N (and C) in some soil pools and possibly increased mineralization of N. STUDYING THE EFFECT OF ORGANIC MATTER, WATER MANAGEMENT AND INOCULATION ON NUTRIENT TURNOVER AND BIOLOGICAL NITROGEN FIXATION OF CERTAIN PLANTS USING ISOTOPE TECHNIQUES. M.S.A. Safwat, T.M.M. Moharram, M.A.O. El-Hohandes and M.A.M.Badawi Dept. of Agricultural Microbiology, Minia University, Minia, EGYPT. Pots and field experiments will be conducted to study the effect of organic matter (e.g. plant residues, compost and animal manure), water management (e.g. surface and sprinkler irrigation) and

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inoculation on nutrient turnover, micronutrients, biological nitrogen fixation and the synchronization of nutrient release and plant nutrient demand of various crops. Field experiments will be carried out on the newly reclaimed sandy soils at Shosha. SOIL ORGANIC CARBON AND NITROGEN CYCLING UNDER DIFFERENT CROP ROTATIONS AND TILLAGE PRACTICES IN AN IRRIGATED VERTISOL IN CENTRAL MEXICO. J.Z. Castellanos and R.F. Follett Campo Experimental Bajio-INIFAP Celaya, Guanajuato, MEXICO. Vertisols are one of the most widely distributed soils in the world. In Mexico, they occupy an important area of irrigated and rainfed agriculture and are mainly in the center of the country, producing one fourth of the wheat and one fifth of the corn and sorghum. Unfortunately, for at least 50 years crop residues have been burned and these soils are deeply and frequently plowed. Long-term records indicate that the levels of soil organic carbon (C) have been reduced to 60 or 70 % of original values due to these practices. Loss of soil organic matter in these soils has decreased their N-supplying capacity to only about 20 to 40 kg N/ha per crop. Thus, these soils have severely decreased capacity for mineralizing N for crop production, to support an active microbial biomass for nutrient retention and cycling, to retain applied pesticides, and they also have lower water-holding capacity than do soils with higher soil organic matter levels. An important additional problem is the leaching of nitrates from the fertilizer N that is applied to overcome the N deficiency of these soils. Such leaching into groundwater decreases the quality of well water that is used for drinking. The current practice is to produce two crops per year under irrigated conditions and to burn the residue of both crops to facilitate ploughing. An effective alternative for these soils is proper management of the crop residues, with conservation tillage, including no till. Return of crop-residue C and the judicious use of N-fertilizer should begin rebuilding the soil organic matter and the fertility of these important Mexican soils, but very few studies have been conducted to assess the effects of conservation tillage on soil organic matter. No studies have been conducted using 15N/14N or 13C/12C isotope ratio technology to measure the effects of conservation tillage on N-cycling dynamics, fertilizer N-use efficiency, and crop-residue C sequestration into vertisols; such information will be of direct relevance to Mexico and to other similar areas. THE USE OF ISOTOPE TECHNIQUES IN STUDIES ON THE MANAGEMENT OF ORGANIC MATTER FOR SUSTAINABLE AGRICULTURAL PRODUCTION IN SOUTH VIETNAM Phan Thi Cong, Department of Soils and Fertilizers Institute of Agricultural Science of South Vietnam Ho Chi Minh City, VIETNAM Due to intensive and prolonged weathering most of the soils in Vietnam are poor in nutrients. Declines in soil organic matter content after deforestation cause severe reductions in the mineralization of nutrients for crops and in the nutrient sorption capacity of the soils. Moreover, they threaten weakly-structured soils, such as Acrisols. Decreases in SOM, therefore threaten the

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sustainability of upland agro-ecosystems The objectives of this study are: i) to increase the quantity of nutrients available to crops with judicious mixtures of inorganic and organic sources, ii) to assess the effectiveness of organic residue and inorganic fertilizers on the building of soil organic matter and the release of plant nutrients through isotopic labelling, iii) to investigate whether soil organic fractions can be used as early and sensitive indicators of the sustainability of the upland agro-ecosystem and iv) to improve process-level understanding of carbon and nutrient flows by the use of isotopic techniques and computer models, so that management recommendations can be extrapolated to a wide range of environments. In order to reach these objectives, the following activities will be implemented: 1) install micro-plots with 15N, and double-labelled (15N-14C) plant material into existing field experiments for monitoring C dynamics; 2) investigate the decomposition and transformation of different organic sources into soil organic matter; 3) study the chrono- and topo-sequence with clear-cut C3-C4 transitions using 13C; and 4) investigate transformations of P in soils with low P availability (Haplic Acrisol and Rhodic Ferralsol) using 32P-labelled fertilizer and plant-residue material. DECOMPOSITION OF 15N AND 14C LABELLED RESIDUES IN VOLCANIC SOILS OF THE CHILEAN CENTRAL PLAIN. Erick Zagal and Ivan Vidal Universidad de Concepcion, Faculty of Agronomy, Department of Soils, P. 0. Box 537, Nicasio Rodrigues, INIA, Chillan, CHILE. Jan Persson and Gerd Johansson, Department of Soil Sciences, Swedish University of Agricultural Sciences, Uppsala, SWEDEN. The main agricultural region in Chile lies in the central plain. Major crops are produced here, e.g. wheat, maize, beans, potatoes, sugar beets. The soil types of the region are of alluvial and volcanic origin. Volcanic-ash derived soils (Andepts or Andosols) dominate the latter. Studies on organic matter show that the allophane content in ash-volcanic derived soils causes a major decrease in the degradation of added carbonaceous materials as compared to non allophanic soils; the reasons are unclear. A project is proposed with the general aim of studying decomposition of 15N- and 14C- labelled residues in irrigated volcanic soils with different crop rotations and levels of fertilization. Specific aims are: i) to determine rate of decomposition of labelled material with different quality (i.e. maize stems and roots); ii) to evaluate possible nutrient limitations (N, P) in the process of decomposition; iii) to quantify gross mineralization-immobilization rates. The approach will be a field experiment complemented with laboratory incubations. The field experiment is located in an irrigated valley. The climate is Mediterranean. The experiment (microplots) will be installed within the larger scale plots of an established experiment, which is an agronomic study of rotations with two levels of fertilization in irrigated soils of volcanic origin. The experiment has a split-plot design with four replicates (blocks), with rotation treatment as the main plot and level of fertilization as the subplot. The levels of fertilization are: high and medium. Four treatments (rotations) with and without livestock are considered: i) Sugar beet-Wheat-Red clover-Red clover with livestock; ii) Sugar beet-Wheat-Common Bean-Barley without livestock; iii) Maize-Wheat-Red clover-Red clover with livestock; iv) Maize-Wheat-Common Bean-Barley (annual crops) without livestock. Maize plants are labelled in rotations iii) and iv) during spring season 1996 (first week of November). Winter wheat plants are labelled during autumn 1997 (April/May). After harvest, labelled material is applied to microplots different from those used for labelling. 15N-labelled

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maize residues are applied during the autumn of 1997 before winter wheat. 15N- labelled wheat residues are applied during autumn of 1998 before clover. Doubly-labelled (14C-15N) wheat residues are added in 1-2 kg plastic tubes within the microplots. Samples of plants, soil and remaining residues will be collected at 3 weeks, 3, 6 and 12 months, and for the duration of the experiment. Collected materials will be analyzed for total N, 15N, total C, and 14 C. Determinations of soil biomass and inorganic nitrogen will be made. ORGANIC MATTER MANAGEMENT FOR INCREASED AND SUSTAINABLE AGRICULTURAL PRODUCTION IN BANGLADESH. S. M. Rahman, M. I. Khalil, M.E. Haque and M.A. Wohab Mia Bangladesh Institute of Nuclear Agriculture, Mymensingh-2200, BANGLADESH. Agronomic experiments (non-isotopic) were conducted in a grey floodplain soil (Haplaquepts) in Bangladesh for several years to study tillage and manuring effects on crop yields, soil-physical properties and water relations in a sustainable land-management system. The objectives included studies on the effects of application of organic manures (crop residues and decomposed farm yard manure, FYM) incorporated into the soil alone or in combination with chemical fertilizers under different tillage practices, on increasing soil organic matter (SOM), nutrient status, and crop yield. The neutron probe was used to study the water relations at various stages. Results indicated no significant effect on the wheat yield due to the tillage practice. Highest yield was recorded in plots receiving the locally recommended dose of NPKSZn fertilizers, followed by treatments receiving FYM or rice straw each at 6 t ha-1 along with half of the recommended doses of chemical fertilizers. FYM and/or rice straw applied singly or in combination did not produce a comparable wheat yield. Residual effects- of manuring were not observed in summer mung bean, but rice yield were increased considerably without any application of manuring and/or chemical fertilizers except urea, indicating a substantial contribution of nutrients from prior manuring and tillage practices. SOM was always higher in the 0-1.0 cm depth and considerably lower at 20-30 cm. It would be premature to discuss changes in SOM at the end of only a three-year study. However it has been reported that tropical soils when continuously cultivated, lose SOM dramatically. The water-holding capacity of our soil showed no significant change, but ranged between 45 and 55 per cent in different treatment plots and remained largely unchanged over the three-year period. GEOSTATISTICAL STUDIES APPLIED TO AMAZONIAN SOILS: ORGANIC MATTER RELATED PROPERTIES IN A FOREST-PASTURE SUCCESSION O.O.S. Bacchi, M. Bernoux, C.C. Cerri, D. Dourado, B. Feigl, and K. Reichardt. Center for Nuclear Energy in Agriculture Piracicaba, BRAZIL. The study consists of a landscape-scale study, using geostatistical methodologies to analyze and characterize the spatial variability of soil parameters related to soil organic matter, in a forest-pasture succession, in the State of Rondonia, Brazil. The great majority of soil nutrient storage estimates in a global or regional scale is based on the extrapolation of averages considering soil classes or categories and vegetation types. There is much uncertainty in these estimates. The use of

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Geographic Information Systems (GIS) is improving estimates, but there is still need to consider the spatial variability within each soil unit. Geostatistical characterization of several physico-chemical properties of the soil, which is the scope of this project, will certainly improve results. Through this information it is intended to better understand the dynamics of organic matter in Amazonian forest-pasture systems, in order to enhance soil productivity and assure sustainability. This first report presents a general overview of the carbon cycle and details for sugar-cane and pasture systems. Sampling locations, scales and schemes are shown in relation to geostatistical analyses that will be made in future. Preliminary results are presented in the form of semi-variograms, for some of the measured soil properties, e.g. pH, soil bulk density, 13C, soil moisture, total carbon, exchangeable cations. STUDIES ON ORGANIC MATTER TURNOVER AND BUILD-UP IN ULTISOLS AND OXISOLS IN SIERRA LEONE. Denis Amara Institute of Agricultural Research, Department of Soil Science PNM 540, Freetown, SIERRA LEONE. The majority of the upland soils in Sierra Leone are ultisols or oxisols that are generally low in fertility as a consequence of intensive weathering and leaching of nutrients by heavy rainfall. The soil fertility problem is exacerbated by the shortening of the bush-fallow period and the increasing demand on agricultural land. Despite this, very few farmers use fertilizers to replenish soil fertility, and even the large amounts of crop residues obtained at the end of the cropping season are not properly managed as a source of nutrients and soil organic matter. Since crop residues and prunings of multipurpose trees are potential sources of nutrients and organic matter in our cropping systems, the following experiments have been designed to provide an understanding of how best they may provide nutrients and build up soil organic matter: (i) Improve residue management in a crop rotation, (ii) determine the N uptake from organic (crop residues) and inorganic sources and (iii) determine the decomposition of 15N- and 14C- labelled crop residues and prunings of multipurpose trees. It is anticipated that results obtained from this research will provide guidance in the management of crop residues and prunings of multipurpose trees to maintain the physical, chemical, and biological properties of soils in the upland agro-ecosystems of Sierra Leone. MANAGEMENT OF SOIL ORGANIC MATTER TO ENHANCE SOIL PRODUCTIVITY AND SUSTAINABILITY IN SRI LANKA Ravi Sangakkara Faculty of Agriculture, University of Peradeniya, SRI LANKA. The agricultural production systems of Sri Lanka consist of two well-defined components. One is the plantation sector established during the colonial era, and the other is the smallholder subsistence sector producing food crops. While the traditional systems of Sri Lankan agriculture was based on organic manures and amendments, the advent of the green revolution and the availability of chemical fertilizers at low prices enhanced the use of agro-chemicals at the expense of adding organic matter. This has led to the depletion of soil organic matter, especially under moist tropical humid conditions, resulting in low productivity of the current chemical-based agricultural sectors, along with low soil fertility and the lack of sustainability of the farming

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systems. Furthermore, farmers using organic matter apply different rates haphazardly, leading to the inefficient use of the added material. 7. Experimental Co-ordination As part of the CRP, designed experiments will be carried out by each Contract Holder, to serve as a common thread fostering a co-ordinated effort. In order to achieve such a linkage, the experiments should meet the following conditions: (i) They can be carried out by every participant. (ii) They are a mixture of basic and applied research. (iii) The objective(s) are realistic, focussed and can be met within the means and

resources available to each Contract Holder. (iv) They should be designed with a holistic approach within the framework of a

cropping system, rather than focussed on one of its individual components. (v) Data and results produced by each Contract Holder will have value for every

participant. With these conditions in mind, a series of experiments was proposed. After full discussion, each participant agreed to carry out the following experiments: Experiment A Main objective To assess whether an adapted residue-management system enhances the

potential to retain the added nutrients within the crop:soil system with concomitant increases in yields.

The main question to be addressed is whether the application of organic residues will lead to an increase in nutrient-use efficiency by the crop, with reduction in nutrient loss from the cropping system. If the organic amendments lead to greater nutrient retention and uptake, the cropping system will become more sustainable and crop productivity will be maintained. The efficiency of nutrient use will not be appraised solely on its recovery by the first crop, but rather will be based on the total amounts of nutrient recovered in the crops plus the various soil pools after several years. Experimental protocol All Contract Holders have or will have field studies under way to determine the role of organic amendments on soil quality and crop production. Some have already established rotation studies that include organic amendments; others will initiate similar studies. The contract holders were selected from 12 countries, representing three continents. Therefore, 12 different cropping systems will be tested, with control treatments reflecting current farmers' practice: absence of residue due either to burning or removal. In the adapted farming practice, the application of residue or other amendment with some other organic material will become part of the cropping system. Also possible is inclusion of a new management practice consisting of partial-removal/partial reapplication of crop residue; this treatment has relevance in countries in which crop residues have an important use, for example for feeding livestock.

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Step 1 Selection If the contract holder is already involved in a study of many different rotations, he/she will select two for this study: a) the control rotation and, b) one of the more promising rotations that uses organic amendments to improve

yield. Because of time and funding limitations, no more than two rotations can be chosen. If a crop-rotation study does not exist or cannot be used, a new one will be initiated. Experiment A, superimposed on an existing rotation experiment or newly initiated, will consist of four treatments: Treatment 1: will determine the flow and fate of 15N-labelled fertilizer when residues are

added. Treatment 2: will determine the flow and fate of 15N-labelled residue when residues are

added. Treatment 3: will be used to generate unlabelled residues. Treatment 4: will be used to determine the flow and fate of 15N-labelled fertilizer when

no residue is added. An example of a possible crop rotation study is included (Figs. 1 to 12): a wheat-bean rotation with two growing seasons per year. The control treatment (T4) consists of the removal of the residues. For the improved rotation (T1 and T2), the residues are left on the field. The experimental layout is presented in Fig. 1. It has a randomized complete block design, replicated four times. Individual plot size is 8 x 20 m (160 m2) with a 15N microplot of 4 x 4 m. The dimensions for the individual plots, however, are somewhat flexible and may depend on the size of the individual plots used in an already-existing crop-rotation study. The four corners of the 15N microplot will be marked such that they can always be precisely located, even after 5 years. Because the plot size is rather large, there should be no need to put a frame or barrier around the 15N microplot. Step 2 Measurements to be taken at the initiation of the experiment Soil moisture at field capacity Soil texture pH CEC (cation exchange capacity) EC (electrical conductivity to test for salinity) Available N Available K and Organic and inorganic P The method to be used to measure available P should be that most suitable for the soil. All the other methods are well explained in Methods of Soil Analysis, published by the Agronomy Society of America, USA. All efforts should be made to record precipitation and temperature for the duration of the experiment, because crop growth and mineralization of residues are affected by soil moisture and soil temperature. If soil temperature cannot be recorded, air temperature alone is an acceptable alternative. Gravimetric soil moisture content should be determined at the beginning and at physiological maturity of the crop for every growing season over five years. See Methods of Soil Analysis for details on how to measure gravimetric soil moisture content, or contact Klaus

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Reichardt for details. Fertilization of the field: for Contract Holders residing in countries where farmers use fertilizers, the plots should be fertilized according to standard farming practices for the crop rotation being evaluated. Step 3 Labelling the soil with 15N The purpose of adding the label is to follow the fate of N in the cropping system. Only one crop should be labelled with 15N. It is unimportant which crop receives 15N-fertilizer as the objective is to get the 15N into the system. However, the crop that receives labelled fertilizers should also be able to produce a sufficient quantity of highly labelled residue that can be followed for a number of years. In the example provided, the wheat was used to obtain highly 15N-labelled residue, whereas the bean never receives labelled 15N-fertilizer. Contract Holders who have an existing crop-rotation study will initiate Experiment A with the crop selected to receive labelled fertilizer. NOTE: EXPERIMENT A WILL BE REPEATED THE FOLLOWING YEAR Once the soil is labelled with 15N fertilizer at the initiation of Experiment A, the fate of the label be determined for up to five years in every crop as well as in the various soil fractions. Because the 15N-label will be traced for several years, the fertilizer will be applied in the first year at 60 kg/N/ha-1 with an enrichment of 10 atom % 15N. For comparison purposes, all participants should use ammonium sulfate as it is the least expensive form of 15N and volatilization losses from it usually are low; such losses can be high with urea. The cropping systems will differ with each Contract Holder. However, all participants should use the same strategy and sampling scheme for the 5-year period (See Figs. 1 to 12). Two crops will be grown each year. The individual plot size in this example is 8 x 12 m: the 15N microplot measures 4 x 4 m. During the 5-year period, a total of 10 crops are grown: five of wheat and five of bean. Here, the decision was made to label the wheat residue. In Figs. 3 to 12, the main activities of the 5-year wheat-bean rotation study are described. Each participant should follow this example, adapting it to his/her own experiment. In Year 1, the labelled 15N fertilizer is applied in T1 and T4 to wheat in Growing Season 1 (Fig. 2, at seeding). The 15N label should be applied as homogeneously as possible. This can be accomplished by dividing the 15N microplot, 4 x 4 m, into 16 1-m2 sections (Fig. 2). All the 15N required for the entire experiment (for all 15N microplots of the two treatments that receive 15N, i.e., T1 and T4, ) will be dissolved in water. The total number of 15N microplots is: 2 treatments x 4 replicates = 8. Each microplot is divided into 16 sub-microplots; total number of sub-microplots is 8 x 16 = 128. To allow for some losses during the application, make a 15N stock solution of 13 L, sufficient to label 130 sub-microplots. Every 15N subplot will receive 100 mL of the stock solution (keep some for an enrichment- analysis check, see Annex 1). Put 100 mL of the stock solution in a watering can, add 7 L of water and apply to the sub-microplot. To make sure that you apply the solution evenly across the entire sub-microplot, place 20 or more small containers on an area equal to that of the microplot, and apply ordinary water from the watering can to determine how uniformly you can distribute the solution across 1 m2. All of the containers must receive similar amounts of water; do not practice on an actual 15N microplot as it may cause waterlogging. When should the labelled fertilizer be applied? To maximize the N-use efficiency by the crop and to minimize N losses, it will not all be applied at time of seeding, but instead split into four applications: 1) 25 % of the total amount, i.e., 15 kg 15N ha-1, applied at time of seeding, 2) 25% of the total amount, i.e., 15 kg 15N ha-1, applied 2 weeks after seeding,

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3) 25 % of the total amount, i.e., 15 kg 15N ha-1, applied 4 weeks after seeding, 4) 25 % of the total amount, i.e., 15 kg15N/ha-1, applied 6 weeks after seeding. To calculate the amount of 15N-ammonium sulfate required per application of 15N, sufficient for 130 sub-microplots: - Total area to be labelled: 130 x 1 m2 = 130 m2. - Rate is 15 kg N ha-1 which is equivalent to 1.5 g N m-2. - Amount of N needed: 1.5 x 130 = 195 g N per application. - Percent N in ammonium sulfate is 21%. - Amount of ammonium sulfate needed is: 195 x 1/0.21 = 928.6 g per application. Only the 15N microplots will receive N in split applications. The main yield plot can be fertilized as it is commonly done by local farmers. When applying the labelled fertilizer after the crop has already emerged, unavoidably some of the 15N-labelled solution will moisten the leaves. After applying the 15N labelled solution, the 15N on the leaves must be washed off with ordinary water. Plants can absorb N through the leaves, but for comparison purposes all the 15N label that will be accumulated by the crop should have passed through the soil. Although not discussed at the meeting, a soil sample (0 - 15 cm) should be taken from the T1 and T4 plots directly after the label is applied for the FIRST TIME (time of seeding) in order to determine whether 100 % of the applied label can be recovered. To calculate the recovery, the bulk density of the soil must be known. In some cases, farmers may use more than 60 kg N ha-1 to fertilize their crops. If, for example, farmers routinely apply 100 kg/N/ha-1, unlabelled 14N ammonium sulfate should be added to the solution. The unlabelled fertilizer N can be applied at time of seeding and does not have to be split among the four applications. In other cases, farmers may not use fertilizer at all. In that instance, only the 15N microplot will receive the labelled fertilizer, not the yield plot. Although the 15N microplot will likely show an N response, yield determinations for the experiment will not be based on the yield of the 15N microplots. Yields will be taken from the unfertilized part of the plot (Fig. 2) that is set aside for such determinations. Immediately following the harvest of the wheat crop, the 15N-labelled wheat residue from the T1 microplot (the entire 4 x 4 m) will be moved to the new 15N microplot in T2 (Fig. 3, At harvest). The 15N-labelled wheat residue must be homogenized before it is re-applied and a sub-sample saved for the determination of total N and atom%15N (See Annex 1). For subsequent growing seasons during the study, 15N-labelled residues should always be removed at once after harvest, not immediately prior to seeding the following crop (Figs. 3 - 12). As soon as the 15N-labelled residues have been removed from T1 and T4, unlabelled residues from T3 should be moved to the 15N-microplots in T1 and T4 (Figs. 3 - 12). To avoid any effect on the yield and residue quality of subsequent crops in T3 due to the removal of the residue from an area twice the size of 4 x 4 m (32 m2), the remaining residue in T3 should be spread evenly across the entire area of T3 plot (160 m2). Step 4 Sampling the 15N-microplot for soil and plant samples. Soil samples: Because of heterogeneity, all four center sub-microplots within the large 15N microplot (Fig. 2) should be sampled. The outside sub-microplots cannot be sampled for 15N analysis because

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of border effects that may cause additional dilution of the 15N. In this study, the border of the 15N microplot is set at 1 m, which is wider than often used but made necessary by the long-term duration of the experiment. The size of the sample taken from the sub-plot should be small and not cause great disturbance of the soil. Small soil cores are recommended: 1 to 1.5 cm in diameter with two samples taken per sub-microplot (2 x 4 = 8 samples) located in the center of the larger 15N-microplot. The eight samples will be mixed and homogenized and only one soil or plant sample will be analyzed for total N and atom %15N (see Annex 1). This should always be the practice when sampling for recovery of 15N in the soil or in plant residue and seed. Similarly, when sampling the soil for different fractions, a small soil sample should be taken from each of the 9 sub-microplots (located in the center of the larger 15N microplot (Fig. 2) with the 9 soil samples mixed before carrying out the separation. The soil samples are collected four times: a) Immediately after the application of the labelled fertilizer (T1 and T4, beginning of

growing season, Year 1) or labelled residue (T2, end of growing season 1, year 1). Only the total soil N pool will be analyzed for 15N.

b) At the end of the first growing season of the first year for T1 and T4, and at the end of the second growing season of the first year for T2. The soil will be sampled by three depths, and the total soil analyzed at each depth for atom % 15N, and also the five soil organic matter fractions (see below) analyzed at each depth for atom % 15N.

c) At the end of the first growing season of the third year for T1 and T4, and at the end of the second growing season of the third year for T2, again sampling the soil by three depths, analyzing total soil per depth for atom % 15N and analyzing the five soil organic matter fractions at each depth for atom % 15 N.

d) At the end of the first growing season of the fifth year for T1 and T4, and at the end of the second growing season of the fifth year for T2, again sampling the soil by three depths, analyzing total soil per depth for atom % 15N, and analyzing the five soil organic matter fractions of each depth for atom % 15N.

Fractionating the soil organic matter: The soil sample taken from the 15N microplots in T1 and T4 (first, third and fifth years described above under 2, 3, and 4 on when to sample the soil for 15N) should be taken from three depths: (0-15, 15-30, and 30-50 cm). In addition, in Year 5, soil samples should be collected also from the 50 - 75 cm and 75- to 90 cm depths. At that stage of the study, some of the 15N might have leached below the 50 cm but still lie within reach of roots. The N that is within reach of roots is considered to be within the cropping system, therefore, sampling must be done to a depth where roots are sparse. Determine bulk density for all three depths and separate the soil organic matter of each depth into five fractions: fraction 1: soil organic matter floats in water fraction 2: soil organic matter remains in suspension fraction 3: soil organic matter associated with the sand fraction fraction 4: soil organic matter associated with the silt fraction fraction 5: soil organic matter associated with the clay fraction. A detailed description of how to separate soil organic matter into these various fractions is provided in the TSBF book, a copy of which will be sent to you. Why is it necessary to analyze the different fractions of the soil organic matter for 15N? The main purpose is to determine how the different fractions reflect the relative usage of inorganic (T1) versus organic N (T2). Does the use of organic N lead to an increase in 15N in one of the more stable soil organic matter fractions? If so, will this lead to a longer memory effect in regard to the

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N-supply power of the soil when an inorganic or organic form of N is used? Furthermore, every time an 15N budget of the entire cropping system is compiled, possible differences in the total recovery of 15N between inorganic versus organic N can be traced back to the different soil organic matter pools, each with its own turn-over rate. Information on the changes in the size of 15N pool over time will provide basic information that can be used for modeling purposes as further discussed in Experiment 3. As stated earlier, every time a crop is grown on the 15N microplots (T1, T2, and T4), the labelled residue is removed and replaced with unlabelled residue obtained from T3. Only for the T1 and T2 treatments is the labelled residue substituted by unlabelled residue. As there is no residue in T4 (control plot), labelled as well as unlabelled residues are removed (Figs. 3 - 12). Plant samples: In the example of the wheat-bean crop rotation, plant samples are collected 10 times: 5 times for wheat and five times for bean. Total seed and residue yield will be determined 10 times. A subsample of the seed and the residue of every harvest period will be collected from the 15N microplot for total N and 15N isotopic determination. Like sampling the soil for 15N, at least 2 plants per sub-microplot (8 in total) will be collected, separated into residue and grain, mixed and a subsample of both grain and straw finely ground for isotopic analysis (see Annex 1). After several growing seasons, it is unlikely that the crop will show a 15N enrichment above background. However, plant samples still need to be processed for percent N in order to calculate total N accumulation in the crop. When soil and plant samples are sent to Vienna for analysis, all samples will be analyzed for %N, %C, atom %15N and atom %13C (see Annex 1). Optional additions There are numerous other experiments that may be included in Experiment A, but which will not become part of the series of experiments to be carried out by every contract holder. Some examples for such optional experiments are: a) Determine the availability of P (rock phosphate) as affected by organic amendments

using isotope-dilution techniques. b) Follow the size of the microbial biomass as affected by organic additions and its

strength as a temporal sink for 15N. c) Estimate N2 fixation by legumes when present in the cropping system. d) Follow changes in root diseases (fungi, root rot) as induced by the addition of

organic residues. e) Determine changes in physical/chemical properties of the soil: water-holding

capacity, aggregate size, depth of root penetration, infiltration rate. f) Determine soil erosion losses using 137Cs. Experiment B. Main objective To synchronize the release of nutrients from organic amendments with

nutrient uptake by the crop. Often, there is poor recovery by the crop of nutrients mineralized from organic residues. One explanation is that the time of release from the organic residue does not coincide with the period of high nutrient demand and uptake by the crop. Nutrients, particularly N, that accumulate

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in an available form in the soil, are prone to heavy losses and therefore avenues must be sought to synchronize the release of nutrients from the organic amendments with their uptake by the crop. Experimental protocol If it is found that the release of nutrients from organic amendments does not occur during the period of maximum nutrient uptake, changes in management practices can be proposed to improve the synchrony and hence the efficiency of the cropping system to use available nutrients. This experiment will be carried out in the second part of the CRP. In Year 1, Growing Season 1 of Experiment A, residues will be generated that are highly labelled with 15N. Half of the labelled residue is to be used in Experiment A in Year 1, Growing Season 2; residue from T1 that will be used in T2. The labelled residue generated in T4 in Year 1, Growing Season 1 of Experiment A will be used for synchronization studies. The 15N-labelled residue from T4 obtained from the 15N microplot in Year 1, Growing Season 1 is collected from the entire 4 by 4 m plot, homogenized, and a subsample analyzed for N content and atom%15N (see Annex 1). The rate of decomposition and the release of N from the residue will be determined in an incubation study conducted under field conditions in small 15N microplots contained within cylinders. Diameter of the cylinder will be 20 cm, with a length of 50 cm. The quantity of the 15N-labelled residue added will be similar to the quantity of residue harvested. If the total amount of residue harvested in Year 1, Growing Season 1 were 5 tonnes ha-1, the amount to add to the cylinder, diameter 20 cm (i.e. with a radius [r] of 10 cm, 0.1m) would be calculated as follows: The rate of application is 5 tonnes ha-1 = 5,000 kg ha-1 which is equivalent to 500 g m2 The cylinder has a surface area (πr2) of: 3.14 x 0.1 x 0.1 m2 = 0.0314 m2 For 500 g m-2, the residue application will be 500 x 0.0314 = 15.7 g per cylinder Treatments The following sequence can be used, with exact times for application of residue dependent on climate, soil type, residue quality, and cropping system. Furthermore, the residue-application schedule will be adjusted by each researcher based on the results obtained from Experiment A. - Apply residue when the crop that produced the labelled residue is harvested. - Apply residue 2 weeks before the next crop is seeded. - Apply residue at time of sowing the crop. - Apply residue 2 weeks after sowing and the seedlings have emerged. No plants will be grown in the cylinders (and the microplots will be kept free of weeds). The soil in the cylinders will be sampled destructively (see below) for mineral N. To have some confidence in the data set, at least five samplings will necessary. With four replicates and four residue-application dates (above) the total number of cylinders needed will be: 4 residue application dates x 4 replicates x 5 samplings = 80 cylinders. Sampling The soil will be sampled destructively for mineral N content and its atom %15N determined. Soil mineral N will be determined by soil depth: 0 - 15 cm, 15 - 30 cm, and 30 - 50

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cm. Because soil moisture content has to be known in order to calculate the amount of available N per g of soil, a subsample of the soil will be used to determine soil moisture content. Soil extraction will be done with 2 M KCl on 50-g aliquots of homogenized soil in a 1:4 ratio of soil:extractant. Details are reported in Methods in Soil Analysis. Before the determination of the atom %15N content in the solution can be done, a steam distillation or a diffusion has to be carried out. This is necessary to separate the available N (all converted to ammonium) from the KCl, and to concentrate the N in the solution. Details regarding the preparation of the mineral N samples for mass spectrometer analysis will be discussed in full at the next RCM as not all Contract Holders have access to a steam distillation unit or have experience with the diffusion process. Data will be obtained as follows: - Changes in soil mineral N content following the addition of organic amendments. - Atom % 15N excess values of the mineral N pool over time. The N-mineralization data must be viewed in terms of the rate of N uptake by the test crop (N accumulation in kg ha-1 week-1), to determine whether the period of highest demand for N coincides with the period of maximum mineralization of N. The rate of N uptake is determined by harvesting the crop several times throughout the growing season and measuring total yield and total N. Experiment C (TENTATIVE) Main objective To measure to the release of C and N from doubly 15N-13C labelled crop

residues and assess their movement through the various soil pools. There is a number of models available to explore the effect of management practice on changes in C storage in the soil, and how it affects nutrient cycling. The better models are: RothC, CANDY, DNDC, CENTURY, DAISY, SOMM, ITE Forestry/Hurley Pasture Model, Verberne Model, and the NCSOIL. Most of these were validated using data sets from long-term experiments conducted in temperate conditions. It remains to be determined how well they would predict changes in C content in tropical agro-ecosystems. By using 13C-15N doubly-labelled maize residue in different soils and agro-ecological zones, the effects of soil characteristics and climate on the rate of decomposition of C and the availability of N can be determined. With the information generated in Experiment A on N dynamics and agronomic aspects of residue yield and quality, simulation models can be validated using data generated from the twelve sites. With validation, the models can be used to predict long-term impact of crop-residue management practices. Experimental protocol The main objectives of this experiment are to measure the decomposition of a doubly 13C-15N labelled crop residue in different soils and climates and assess movement of released C and N through the various soil pools. Doubly-labelled crop residues will be generated at Seibersdorf for use b all of the Contract Holders. Data generated can be used in models that can predict future changes in soil organic matter content and soil quality as affected by the addition of organic amendments, soil type and climate. The doubly-labelled material will be grown in a greenhouse or large growth chambers with atmosphere enriched with 13C-CO2. The 13C content of the residue should be elevated from 1.1 % to above 3 atom %13C. The test crop is corn, a C4 plant, grown hydroponically in a 15N-enriched solution (5 atom %15N). Above and below ground corn residues will be used for the incubation studies.

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To increase the atom %13C from 1.1 to 3.1 % in a corn plant with a dry weight of 300 g, the amount of 13C required can be calculated as follows: Assume a plant dry weight of 300 g, containing 50% C, which corresponds to 150 g C,

therefore the excess amount of 13C needed is 3.1 x 150 - 1.1 x 150 = 3.15 g 13C per plant. As some 13CO2 will be lost from the incubation chamber and the recovery of the 13CO2 by the plant will not be 100 %, assume a 13CO2 use efficiency of 75 %. Therefore, the total amount required will be 4.2 g of 13C per plant.

As the contract holders will not become involved in the preparation of the doubly labelled material, no further details will be provided here. The doubly-labelled residue will be applied at 10 tonnes ha-1 or 1000 g m-2. Microplots will be in the form of cylinders: 20 cm in diameter and 50 cm long. Over a period of 4 years, the fate of 13C and 15N will be determined 11 times: 4 times in Year 1 (at time 0, and at 3, 6, and 9 months), 3 times in Year 2 (12 and 18 months), Twice in Year 3 (24 and 30 months), Twice in Year 4 (38 and 48 months). No plants will be grown in the cylinders. The cores will be sampled destructively and separated into three depths: 0-15, 15-30, and 30-50 cm. Each soil depth will be analyzed for total 13C and 15N content. Five soil fractions will be obtained as described earlier, and each fraction will be analyzed for 13C and 15N enrichment. A small, preliminary double-labelling experiment will be conducted by the staff at the Soils Unit in Seibersdorf. Once those results are known, 13C and 15N doubly-labelled corn residue will be generated and distributed to Contract Holders. As this experiment will not be conducted during the first two years of the CRP, a detailed description of the experiment is not warranted here, but will be provided at the next RCM. General Comment The Experiments described under A and B can be used, following modifications and adaptations to suit local conditions, by Contract Holders as a basis to apply for additional funding from local, national or overseas granting agencies. As stated earlier, the support received from FAO/IAEA can be used as seed money. The possibility of success in generating additional funding will improve when there is evidence that another agency, i.e., FAO/IAEA, has approved the proposal for partial funding.

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8. Suggested references Books: 1. Tropical soil biology and fertility: a Handbook of Methods. 1993. Second Edition. Eds.

J.M. Anderson and J.S.I. Ingram. CAB International. Wallingford, Oxon OX10 8DE, UK. 2. Methods in soil analysis: physical and mineralogical methods. 1986. Ed. A. Klute.

Agronomy Society of America (ASA) and Soil Science Society of America (SSSA). ISBN 0-89118-811-8.

3. Methods in soil analysis: chemical and microbiological properties. 1982. Eds. A.L. Page et al. ASA and SSSA. ISBN 00-89118-072-9.

4. Methods in soil analysis: microbial and biochemical properties. 1994. ASA and SSSA. Eds. R.W. Weaver et al. ISBN 0-89118-810-X.

5. Evaluation of soil organic matter models. Using existing long-term datasets. 1996. Eds. D.S. Powlson, P. Smith and J.U. Smith. Springer Verlag.

6. Soil microbiology and biochemistry. 1989. E.A. Paul and F.E. Clark. Academic Press 7. Microbial production and consumption of greenhouse gases: methane, nitrogen oxide and

halomethanes. 1991. J.E. Rogers, and W.B. Whitman. American Society of Microbiology. 8. Stable isotopes in ecological research. 1989. P.W. Rundel, J.R. Ehleringer, and K.A. Nagy.

Springer-Verlag. 9. Cycles of soil. Carbon, nitrogen, phosphorus, sulfur, micronutrients. 1986. F.J. Stevenson.

Wiley and Sons. 10. Humus chemistry. 1982. F.J. Stevenson. Wiley and Sons. 11. Dynamics of soil organic matter in tropical ecosystems. 1989. D.C. Coleman, J.M. Oades,

and G. Uehara. Un. of Hawaii Press. 12. Carbon isotope techniques. 1991. D.C. Coleman and B. Fry. Academic Press. 13. Soil organic matter dynamics and sustainability of tropical agriculture. 1993. K. Mulongoy

and R. Merckx. Wiley and Son. 14. Stable isotopes in ecology and environmental science. 1994. K. Lajtha and R.H. Michener.

Blackwell Scientific Publications. 15. Plant physiological ecology. Field methods and instrumentation. R.W. Pearcy, J.

Ehleringer, H.A. Mooney, and P.W. Rundel. Chapman and Hall. 16. Biogeochemistry. An analysis of global change. 1991. W.H. Schlesinger. Academic Press. 17. Soil biology and soil quality. 1994. Advances in soil science. J.L. Hatfield and B.A.

Stewart. Lewis Publishers. 18. Mass spectrometry of soils. 1996. Eds. T.W. Boutton and S. Yamasaki. M. Dekker. Articles: 1. Tiessen, H., and J.W.B. Stewart. 1983. Particle size fractions and their use in studies of soil

organic matter. II. Cultivation effects on organic matter composition in soil. Soil Sci. Soc. Am. J. 47:509-514..

2. Balesdent, J., A. Mariotti, and B. Guillet. 1987. Natural 13C abundance as a tracer for soil organic matter dynamics studies. Soil Biol. Biochem. 19:25-30.

3. Balesdent, J., G.H. Wagner, and A. Marioti. 1988. Soil organic matter turnover in long-term field experiments as revealed by carbon-13 natural abundance. Soil Sci. Soc. Am. J. 52: 118-124.

4. Jenkinson, D.S., and J.H. Rayer. 1977. The turnover of soil organic matter in some of the Rothamsted classical experiments. Soil Sci. 123:298-305.

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5. Christensen, B.T. 1992. Physical fractionation of soil and organic matter in primary particle size and density separates. Pages 1-90. in B.A. Stewart (ed). Advances in Soil Science, Vol. 20, Springer Verlag, Inc. New York.

6. Bonde, T.A., B.T. Christensen, and C.C. Cerri. 1992. Dynamics of soil organic matter as reflected by natural 13C abundance in particle size fractions of forested and cultivated oxisols. Soil Biol. Biochem. 24:275-277.

7. Vitorello, V.A. , C.C. Cerri, F. Andreux, C. Feller, and R.L. Victoria. 1989. Organic matter and natural carbon-13 distribution in forested and cultivated oxisols. Soil Sci. Soc. Am. J. 53:773-778.

8. Jarvis, S.C., E.A. Stockdale, M.A. Shepherd, and D.S. Powlson. 1996. Nitrogen mineralization in temperate agricultural soils: processes and measurement. In: Advances of Agronomy. pp 187-235. Academic Press.

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Annex 1 INSTRUCTIONS FOR PREPARATION AND

IDENTIFICATION OF SAMPLES SENT TO THE IAEA LABORATORY FOR 14N/l5N RATIO/TOTAL NITROGEN ANALYSES

I. PLANT SAMPLES 1. The samples have to be oven-dried and finely ground (particle size <0.5mm), approximate amount: l g. 2. The coding of the samples has clearly to indicate: a) the treatment number, b) the replicate number, and c) the origin of plant. e.g.,:2 R1 leaves (Treatment 2, Replicate 1) or 3 R2 stem (Treatment 3, Replicate 2) 3. A list of treatments has to be attached to the samples, indicating e.g.: - the crop species, - the rate of 15N fertilizer application, - the approx. 15N-enrichment of fertilizers, - the time of application, - the time of harvest(s), etc. 4. The 15N-labelled fertilizer(s) used for this specific experiment has(ve) to be send together with the plant samples. In case of solid (homogeneous) fertilizer you must indicate: a) the chemical form, e.g. ammonium sulfate, urea, etc. b) the approximate atom % 15N enrichment. A minimum of 100 mg material is needed. For fertilizer standards in form of solutions, we also need to know the

nitrogen concentration, e.g.: 10 mg N/2 mL or 20 g urea/200 mL. The concentration should not be less than 5 mg N mL-1. A minimum of 1 mL is required. 5. Save an adequate amount of each sample in your laboratory for future analyses if needed. II. SOIL SAMPLES Oven-dried and finely ground soil sample are accepted for analyses provided that they contain at least 0.05% N. Coding instructions are similar as for plant samples. III. EXTRACTS In exceptional cases only, we may accept extracts, provided that they meet the following requirements: a) NO BORIC ACID

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b) The N concentration has to be known and should be of at least 5 mgN/mL

approximate volume: 1 mL.

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Annex 2 LIST OF PARTICIPANTS

Contract Holders Mr. S.M. Rahman (BGD-8895) Bangladesh Institute of Nuclear Agriculture P.O. Box No. 4 Mymensingh-2200 Bangladesh Fax: +880 91 53804 Phone: +880 91 54401 (ofc); 880 91 55178 (res.) +880 91 54047 (ofc) Mr. Klaus Reichardt (BRA-9031) Soil Physics/Soil Chemistry/Agriculture Centro de Energia Nuclear na Agricultura CENA/USP Av. Centenario 303, Cx. Postal 96 13400-970 Piracicaba, SP Brazil Fax:+5519-429 4610 Email: KREICHAR@CARPA.CIAGRI.USP.BR Phone: +5519 429 4600 Mr. Erick Zagal (CHI-9032) Facultad de Agronomía Departamento de Suelos Universidad de Concepción Vicente Méndez 595, Casilla 537 Chillán Chile Fax: +5642-227517 or 221507 Phone: +5642-216333 Email: ezagal@palomo.chillán.udec.cl Mr. Jia Yu Wang (CPR-8896) Soils and Fertilizers Institute Zhejiang Academy of Agricultural Sciences Hangzhou 310021 People's Republic of China Fax: +86571 6094504 Phone: +86571 6040343 ext 2155 (ofc) +86571 6094548 (res)

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Mr. Seth K.A. Danso (GHA-9034) Department of Soil Science University of Ghana Legon-Accra Ghana, West Africa Fax: +23321 500392 Phone: +23321 301190 E-mail: Danso@ug.gn.apc.org Mr. Mohamed S. A. Safwat (EGY-9033) Dept. of Agric. Microbiology Faculty of Agriculture Minia University Minia Egypt Fax: +202 348 7759; +202 349 2472 Email: Entag@Intouch.Com Phone: +2086 322333 ofc; 202 3368624, +202 3519310 res. Ms. Rosenani Abu Bakar (MAL-8897) Universiti Pertanian Malaysia Department of Soil Science 43400 Serdang Selangor Malaysia Fax: +603 9434419 Phone: +603 9486101 ext. 2656/2688 Email: Zauyah@agri.upm.edu.my Mr. Ismaili Mohamed (MOR-9036) Faculte des Sciences Departement des Biologie Universite Moulay Ismail B.P. 4010 Beni M'Hamed Meknes Morocco Fax: c/o UNDP, Rabat +2127701566 or 212 5 536809 Tel.: +212 5 539011 Mr. Javier Z. Castellanos (MEX-9035) Centro de Investigacion Regional del Centro (INIFA) Campo Experimental Bajio Km. 6.5 Carret. Celaya-San Miguel Allende Apdo. 112, Celaya, GTO, 38000

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Mexico Fax: +52 461 15431 Phone: +52 461 16163 Email: casteja@mindvox.ciateq.mx Mr. Denis Amara (SIL-9037) Institute of Agricultural Research Department of Soil Science P.M.B. 540, Freetown Sierra Leone, West Africa Fax: +c/o UNDP 232 22 223250 Telex: c/o UNDP 3299 Phone: c/o UNDP 2255311 225346/2253 E-mail: juliad@Sl.baobab.com Mr. Ravi Sangakkara (SRL-9038) Department of Crop Science Faculty of Agriculture University of Peradeniya Peradeniya Sri Lanka Fax: +94 8232517 or +94 888041 Phone: +94 888375, 888657 [8224496 (res)] Telex: 23046 UPDN CE Email: SANGA@AGRI.PDN.AC.LK Mrs. Phan Thi Cong (VIE-9040) (in lieu of Mr. Nghia Nguyen Dang) Soil and Fertilizer Department Institute of Agricultural Science of South Viet Nam 121 Nguyen Binh Khiem 1 District, Ho Chi Minh City Viet Nam Fax: +848 8297650 Phone: +848 8242108; 8291746 Email: iaskul@cesti.teltic.com.vn

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Agreement Holders Mr. David S. Powlson (UK-9039) Head of Soils Science Department IACR-Rothamsted Harpenden, Hertfordshire AL5 2JQ United Kingdom Fax: +441 582 760981 Phone: +441 582 763133 Email: David.Powlson@bbsrc.ac.uk Mr. N. Sanginga (BEL-9030) (in lieu of R. Merckx, Belgium) International Institute for Tropical Agriculture c/o L.W. Lambourn & Co Carolyn House, 26 Dingwall Road Croydon CR9 3EE United Kingdom Fax: 441 81 6818583 Telex: IITA, Ibadan NG31417+TRO Email: n.sanginga@cgnet.com Scientific Secretary of the Meeting Mr. C. van Kessel Soil and Water Management & Crop Nutrition Section From the Joint FAO/IAEA Division: Mr. J.D. Dargie, Director Mr. C. Hera, Head, Soil and Water Management & Crop Nutrition Section Mr. F. Zapata, First Officer, Soil and Water Management & Crop Nutrition Section Mr. P. Moutonnet, First Officer, Soil and Water Management & Crop Nutrition Section Mr. Allan R. Eaglesham, Visiting Scientist, Soil and Water Management & Crop Nutrition Section Mr. G. Hardarson, Acting Section Head, Soil Science Unit, FAO/IAEA Agriculture and Biotechnology Laboratory, Seibersdorf. Ms. Angela Sessitsch, Soil Science Unit, Seibersdorf Ms. Martina Aigner, Soil Science Unit, Seibersdorf Mr. José Luis Arrillaga, Soil Science Unit, Seibersdorf Mr. Leo Mayr, Soil Science Unit, Seibersdorf Dr. Zaharah Abd. Rahman, Visiting Scientist, Soil Science Unit, Seibersdorf

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Annex 3

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