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COMPETITION ANALYSIS, NITROGEN RESPONSE ANDCANOPY COVER ASSESSMENT IN SUGARCANE

INTERCROPPING SYSTEMS

A DISSERTATION SUBMIITED TO THE GRADUATE DIVISION OF THEUNIVERSITY OF HAWAI'IIN PARTIAL FULFILLMENT OF THE

REQUIREMENTS FOR THE DEGREE OF

DOCTOR OF PHILOSOPHY

IN

AGRONOMY AND SOIL SCIENCE

MAY 1995

By

Maqbool Akhtar

Dissertation Committee:

James A. Silva, ChairpersonRichard E. GreenRobert CaldwellCarl I. Evensen

Kent D. Kobayashi

UMI Number: 9532575

OMI Microform 9532575Copyright 1995, by OMI Company. All rights reserved.

This microform edition is protected against unauthorizedcopying under Title 17, United states Code.

UMI300 North Zeeb RoadAnn Arbor, MI 48103

In the name of GOD, Most Gracious, Most Merciful

* (ALLAH) Most Gracious!

* It is HE Who has Taught the QUR'AN.

* He has created man.

* He has taught him speech (And Intelligence).

* The Sun and the Moon Follow courses (exactly) computed.

* And the herbs and trees - Both (alike) bow in adoration.

* And the Firmament has HE Raised high, and HE has set up The

Balance (of justice),

* In order that ye may Not transgress (due) balance.

* So establish weight with justice And fall not short in the balance.

* It is HE Who has Spread out the earth For (His) creatures:

* Therein is fruit And date palms, producing Spathes (enclosing dates):

* Also corn, with (its) Leaves and stalk for fodder, And sweet smelling

plants.

* Then Which of the Favours Of Your LORD Will ye Deny?

(AL-QUR'AN: Surah 55, Verses 1-13).

Dedicated to:

My Wife Zahida, Daughter Aisha and Sons

Ali and Hasnain.

1lI

IV

ACKNOWLEDGEMENTS

I would like to express my deepest regards and gratitute to my advisor,

Dr. James A. Silva, for his invaluable guidance, support, and encouragement

throughout my graduate program which has made it a rewarding experience and

shall be never forgotton. I sincerely thank Drs. Samir A. EI-Swaify, Robert

Caldwell, Carl I. Evensen and Kent D. Kobayashi for their valuable contributions

as members of the dissertation committee. J would like to sincerely thank Dr.

Richard Green, for adjusting his schedule to serve as a committee member in

the final part of this dissertation.

J am grateful to Drs. Robert Osgood (HSPA) and Carl I. Evensen for their

support in this study and Alberta wheat pool for providing wheat seed. I am also

thankful to my friends Dr. M. Nasir Gazdar, Kevin Grace, Muchdar Soedarjo,

Robert Watung, Ghulam Huissain, Hemant Prasad, Jon Kamemoto, San-Gwang

Hwang, green house technicians Stanley and Servillano, and staff at the

Waimanalo research station for their assistance throughout the course of the

experiment.

My deepset regards and thanks to my parents, my wife and other family

members and my dear brother Tanveer Chaudhry who always supported,

encouraged and inspired me in pursuing this degree.

Financial support provided by USAID through Pakistan Participant

Training Program and Government of Pakistan is gratefully acknowledged.

ABSTRACT

The performance of sugarcane as a 1-year crop in intercropping

systems and the amount of canopy cover, crop residue cover and competition

for N between various crops was assessed in this research. The hypotheses

tested in this field study were that sole cane will require lower N than

intercropped cane for maximum productivity; intercropping will reduce the

yield of sugarcane; and intercropping systems will have higher total

productivity and canopy cover than sole sugarcane. Sugarcane variety

H 74-4527 (from HSPA) was planted as a sole crop and in combination with

Sweet corn (Super Sweet 10) and Wheat (Norstar). Leaf area index, primary

stalk population, stalk height, total dry matter, and cane and sugar yields were

significantly higher in sole cane than in intercropped cane. Application of 300

kg N ha" produced the maximum stalk population, stalk height, and cane yield

in all cropping systems at harvest. Sucker stalk yield was similar in all

cropping systems and applied N had a relatively small effect on sucker stalk

population. Total dry matter and sugar yields were maximum at 150 kg N ha-1

in sole cane and at 300 kg N ha" in intercropped cane. Purity of cane juice

was not affected by the intercrops but was decreased by increasing N levels.

Corn ear yield ha" and total dry matter of wheat ha" were similar in sole and

v

VI

intercrop systems and were highest with 300 kg N ha". Intercropping systems

were more efficient than sole sugarcane in utilizing available resources, such

as, soil and nutrients. The land equivalent ratio for the sugarcane-sweet corn

intercropping system was 2.12 and for the sugarcane-wheat intercropping

system was 1.68. The greatest canopy cover was produced early in the crop

by the sugarcane-wheat intercrop and canopy cover developed most slowly in

sole cane. The slide photographic and line intersect methods were

comparable in assessing crop residue cover at higher N levels. The study

indicates that sugarcane can be successfully grown in an intercropping

system in Hawaii, preferably with sweet corn, and can raise farm productivity.

TABLE OF CONTENTS

Acknowledgements ..Abstract .List of Tables ..List of Figures ..Chapter I: Introduction ..Chapter II: Literature Review ..

Rationale For Advantages in Intercropping .Resource Use ..Yield Stability .Diversity .

Natural Enemy Hypothesis " ..Resource Concentration Hypothesis .

Ecological Niche .Measurements of Competition And IntercropAdvantage .

Land Equivalent Ratio (LER) .Relative Crowding Coefficient ..Agressivity .Competitive Ratio .

Intercropping .Nitrogen .Intercropping And Nitrogen ..Soil Erosion And Intercropping ..Crop Residue Cover .

Chapter III: Materials And Methods .Location And Field Plan ..Cropping Patterns .

Sole Crop Plots ..Intercrop Plots .

Sugarcane - Sweet Corn .Sugarcane - Wheat ..

Fertilizer Application .Field Maintenence .Data Collection And Sampling .

Soil Analysis .

ivv

xixiii

16799

10101010

111112131314193034404242434344444545464646

vu

Crop Residue .Weather Data .Tillering .Crop Growth Rate .

Leaf Area Index .Plant Height ..Canopy Width .Estimation of Plant Canopy CoverAnd Crop Residue Cover .

Final Harvest Data .Final Harvest of Sweet Corn .Final Harvest of Wheat ..Final Harvest of Sugarcane ..

Land Equivalent Ratio (LER) ..Statistical Analysis .

Chapter IV: Performance Of Sugarcane In Sole AndIntercropping Systems At Various Nitrogen Levels ..

Introduction .Results .

Plant Height .Leaf Area Index .Early Stalk Population And Number OfMillable Canes At Harvest .

Early Stalk Population ..Stalk Population At Harvest ..

Stalk Height And Girth .Cane Yield .Total Dry Matter .Estimated Tons Of SugarPer Hectare (ETSHa) ..Purity Of The Cane Juice .Nitrogen Concentration Of Primary StalksAnd Tops (Green Leaves) .Total N Uptake by Primary Stalks And Tops .Total N Uptake by Various Cropping Systems .Land Equivalent Ratio .

Discussion ..

viii

47474848494950

50515152535555

5656595966

737379828690

9292

959899

103105

Conclusions .References .

Chapter V: Response Of Sweet Corn To NitrogenAnd Intercropping .

Introduction .Results .

Plant Height .Ears Per Plant And Fresh WeightPer Ear .Fresh Weight Of Ears Per Hectare .Number Of Grains Per Ear .Leaf Area Index ..Dry Matter Production ..Nitrogen Concentration In PlantsAt Final Harvest .

Discussion .Conclusions .References .

Chapter VI: Performance Of Wheat In Sole AndIntercropping Systems At Various Nitrogen Levels .

Introduction .Results .

Plant Height .Canopy Width .Leaf Area Index .Total Biomass I Total Dry Matter .Nitrogen Concentration In Plants AtFinal Harvest .

Discussion .Conclusions .References .

Chapter VII: Canopy Cover Assessment In SugarcaneIntercropping Systems At Various Nitrogen Levels ..

Introduction .Results .

Canopy Cover .Intercropped Sweet Corn And IntercroppedWheat yields .

-------- --- ._--

IX

119121

126126128128

132135137141142

145148154156

159159162162166170173

173177180182

184184186186

193

Effect Of Cover Crops On Cane AndSugar yields .

Discussion .Conclusions .References .

Chapter VIII: Crop Residue Cover Assessment WithSlide Photographic And Line Intersect Methods .

Introduction .Results .Discussion .Conclusions .References ..

Chapter IX: Summary .Appendix 3.1 Nutrient Status Of The Soil Before PlantingExperiment .Appendix 4.1 Analysis of variance: Sugarcane PlantHeight .Appendix 4.2 Analysis of variance: Sugarcane Leaf AreaIndex .Appendix 4.3 Analysis of variance: Sugarcane stalkpopulation .Appendix 4.4 Analysis of variance: Sugarcane FinalHarvest Data .Appendix 4.5 Analysis of variance: Sugarcane FinalHarvest Data ,.Appendix 5.1 Analysis of Variance: Sweet Corn data ..Appendix 5.2 Analysis of Variance: Sweet Corn data .Appendix 6.1 Analysis of Variance: Wheat data .Appendix 6.2 Analysis of Variance: Wheat Data ..Appendix 7.1 Analysis of Variance: Canopy Cover ..Appendix 8.1 Analysis of Variance: Crop Residue CoverAssessment .

References .

x

193194197198

199199201206208209210

214

215

217

218

219

220221222223224225

226

227

LIST OF TABLES

Table Page4.1 Mean cane plant height (cm) at various nitrogen

levels, during the crop growth period in sale andintercropping systems.................................................. 61

4.2 Mean LAI of sugarcane at various nitrogen levelsin sale and intercropping systems................... 67

4.3 Mean stalk population (103 ha") during differentgrowth stages in sugarcane at various nitrogenlevels and cropping systems........................................ 74

4.4 Average primary & sucker stalk population, height,cane yield, and total biomass (DM) (primary &sucker stalks, tops and dry leaves) of cane at finalharvest......................................................................... 83

4.5 N concentration of sugarcane primary stalks & tops,Total N uptake by sugarcane, Total N uptake byvarious cropping systems, Purity of juice andestimated tons of sugar ha" (ETSHa) at final harvest. 93

4.6 Partial LERs and LERs for various cropping systems. 104

5.1 Average plant height (cm) at various nitrogenlevels in sole and intercropped sweet corn 129

5.2 Mean number of ears per plant, fresh weightper ear (g), and number of grains per ear at variousnitrogen levels in sole and intercropped sweet corn....133

5.3 Mean fresh weight of ears (Mg ha"), dry matter(Tonnes ha") and leaf area index (LAI) at variousnitrogen levels in sole and intercropped sweet cornat final harvest. 138

Xl

Table Page5.4 Mean nitrogen concentration (%) in stems, leaves,

husks and the whole plant at various nitrogen levelsin sole and intercropped sweet corn at final harvest....146

6.1 Mean plant height (cm) at various nitrogen levelsin sole and intercropped wheat. 163

6.2 Mean canopy width (cm) in sole and intercroppedwheat. 167

6.3 Mean leaf area index (LAI), dry matter (T. ha01)and nitrogen concentration (%) in sole andintercropped wheat at various N levels at finalharvest. 171

7.1 Average canopy cover (%) at various growthstages and nitrogen levels in three sugarcanecropping systems 187

8.1 Average crop residue cover (%) assessed by thephotographic and the line intersect methods incorn in sugarcane and wheat in sugarcane...... 203

XlI

LIST OF ILLUSTRATIONS

Figure Page4.1. Relationship between plant height and DAP at

several applied nitrogen levels in sole sugarcane... ... 62

4.2. Relationship between plant height and DAP atseveral applied nitrogen levels in sugarcaneintercropped with sweet corn....................................... 63

4.3. Relationship between plant height and DAP atseveral applied nitrogen levels in sugarcaneintercropped with wheat............................................... 64

4.4. Sugarcane leaf area index vs applied nitrogenat 94 and 130 DAP 70

4.5. Sugarcane leaf area index vs applied nitrogenat 155 and 193 DAP 71

4.6. Sugarcane leaf area index vs applied nitrogenat 228 and 341 DAP..................................................... 72

4.7. Sugarcane stalk population vs applied nitrogenat 98 DAP 75

4.8. Sugarcane stalk population vs applied nitrogenat 129 DAP 77

4.9. Sugarcane stalk population vs applied nitrogenat 185 DAP 78

4.10. Sugarcane stalk population vs age of the cropat 0 and 75 kg N ha-1••..•..............••....•.•.........•..•.....•....• 80

4.11. Sugarcane stalk population vs age of the cropat 150 and 300 kg N ha-1. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 81

--------~-~- ~-

Xlll

Figure Page4.12. Relationship between stalk population at harvest

and applied N. 84

4.13. Relationship between stalk height at harvest andapplied nitrogen (1 year-old cane) 85

4.14. Relationship between stalk girth at harvest andapplied nitrogen (1 year-old cane) 87

4.15. Cane yield (primary &sucker stalks) vs applied N ....... 89

4.16. Relationship between total dry matter and appliednitrogen in sugarcane................................................. 91

4.17. Estimated tons of sugar per hectare vs applied N....... 94

4.18. Purity of cane juice as affected by applied nitrogen..... 96

4.19. Nitrogen concentration in primary stalks andprimary tops of sugarcane vs applied nitrogen............ 97

4.20. Total N uptake by sugarcane at various appliedN levels....................... 100

4.21. Total N uptake by three cropping systems atvarious applied N levels.............................. 102

5.1. Relationship between plant height and DAP at severalapplied nitrogen levels in sole crop sweet corn 130

5.2. Relationship between plant height and DAP atseveral applied nitrogen levels in intercroppedsweet corn 131

5.3. Effect of applied nitrogen on number of ears perplant in sole and intercropped sweet corn 1311

xiv

Figure Page5.4. Effect of applied nitrogen on fresh weight per ear

in sale and intercropped sweet corn 136

5.5. Effect of applied nitrogen on the fresh weight ofears per hectare (tons) in sale and intercroppedsweet corn 139

5.6. Effect of applied nitrogen on the number of grainsper ear in sale and intercropped sweet corn 140

5.7. Effect of applied nitrogen on leaf area index (LAI) insale and intercropped sweet corn at final harvest........143

5.8. Relationship between dry matter yield and appliednitrogen in sale and intercropped sweet corn 144

5.9. N concentration of various plant parts in sale andintercropped sweet corn vs applied N 147

6.1. Plant height vs age of the crop at various nitrogenlevels in sale wheat 164

6.2. Plant height vs age of the crop at various nitrogenlevels in intercropped wheat....................................... 165

6.3. Sale wheat canopy width vs age of the crop atvarious nitrogen levels 168

6.4. Intercropped wheat canopy width vs age of thecrop at various nitrogen levels 169

6.5. Effect of applied nitrogen on LAI in sale andintercropped wheat at final harvest.. 172

6.6. Effect of applied nitrogen on total dry matter (OM)in sole and intercropped wheat.. 174

xv

-- _._._._._- --------- ---_. _.

Figure Page6.7. Effect of applied nitrogen on the N concentration

of sole and intercropped wheat plants at finalharvest. 176

7.1. Relationship between canopy cover and age ofsole sugarcane at applied nitrogen levels 188

7.2. Relationship between canopy cover and age ofsugarcane intercropped with corn at appliednitrogen levels 189

7.3. Relationship between canopy cover and age ofsugarcane intercropped with wheat at appliednitrogen levels 190

8.1. Comparison of crop residue cover assessmentwith the photographic and the line intersectionmethods in sweet corn planted with sugarcane 204

8.2. Comparison of crop residue cover assessmentwith the photographic and the line intersectionmethods in wheat planted with sugarcane 205

XVI

1

CHAPTER I

INTRODUCTION

Sugarcane (Saccharum officinarum L.) is grown in tropical and sub-

tropical regions of the world in a range of climates from hot dry environments

near sea level to cool, moist environments at about 609 meters elevation. It is

the major source of sucrose for the world. Sugar is referred to as a

concentrated food source and is thought to be pure energy. It is used as a

sweetener in many products. Alcohol as a beverage and ethanol as a fuel are

byproducts of sugarcane. Sugar produced from sugarcane is the major

source of income for many countries (Silva, 1989). In 1991, a record 16.02

million tonnes of natural, caloric sweeteners, virtually all cane and beet sugar

and com syrup, were consumed in the United States. On a per capita basis,

consumption was estimated at 63.56 kilograms of caloric sweeteners for each

American (Hawaiian Sugar Planters Association, 1992).

Sugarcane is grown as a monoculture in Hawaii and some of the fields

have been under continuous cultivation for the last 150 years. Hawaii is one

of the few sugar producing areas of the world where the crop age averages

24 months at the time of harvest. The Hawaii yield of sugar is among the

highest in the world, about 23.97 tonnes per hectare (10.7 US tons an acre) in

1991 (Hawaiian Sugar Planters Association, 1992). There are many factors

2

that affect the productivity and profitability of this crop. These factors include

the use of artificial sweeteners, increases in the cost of production, increases

in land prices and uncertain weather conditions. Also there is no single

alternative crop available in Hawaii and in many other countries to replace

sugarcane.

Among the nutrtents, nitrogen is the most important nutrient in

sugarcane production. Sugarcane requires high amounts of nitrogen for its

growth, development and for various physiological functions or processes in

the plant (Clements, 1980; and Jawal & Singh 1974). Nitrogen is the most

frequently deficient nutrient in crop production, therefore, most non-legume

cropping systems require N input. Plants normally contain 1 to 5 % N by

weight. Nitrogen is essential for the formation of proteins in plants and is also

ali integral part of chlorophyll, which is the primary absorber of light energy

needed for photosynthesis. An adequate supply of N is associated with high

photosynthetic activity, vigorous vegetative growth, and a dark green color.

On the other hand, an excess of N delays maturity of crops (Tisdale et al.,

1993).

Land for agricultural purposes is limited in Hawaii and throughout the

world. The area of agricultural land is continuously declining due to several

factors such as urbanization, establishment of industries, heavy soil losses

due to soil erosion, increased acreage of saline soil and alkaline soil, water

logging and other environmental disasters. The use of multiple cropping

systems is one way to increase the efficiency of use of the declining acreage

of agricultural land.

At present, providing food for the increasing human population is a

critical challenge to the current world of agriculture. Traditionally, increased

food production has come from the cultivation and addition of new land to the

existing cultivated area. But in many areas of the world all the land that can

be economically cultivated is already in use. Future food demands of a

rapidly increasing world population must be fulfilled through more efficient

crop production practices on the existing acreage.

Nations and civilizations of the world flourished and declined with the

abundance or shortage of resources (EI-Swaify et al., 1982). Soil and water

are among the most important of these resources. Among these, water is the

resource that may cause heavy soil loss if it is not properly managed. Soil

loss due to water is considered one of the world's most serious problems in

agricultural production. This problem is even of greater importance on steep

lands where soil losses are very high. Soil erosion not only results in heavy

soil losses but also affects the fertility of the soil by removing the top layer of

productive soil.

Since the beginning of settled agriculture, soil erosion has destroyed

430 million hectares of productive land ( Lal, 1988). Multiple cropping is one

3

4

of the many practices that can reduce soil erosion which is considered highly

productive and conserves soil on small farms (Willey, 1979). It includes

sequential cropping that limits the bare fallow time between crops, or

intercropping that limits the spatial extent of bare soil within a field. Farmers

can practice the multiple cropping system by using single, double, triple, or

relay cropping and intercropping.

Various concepts and advantages of intercropping still need more

attention by researchers. Comprehensive studies are required to understand

in depth the agronomic and physiological interactions between the component

species to determine the potential for improving the utilization and

conservation of natural resources. With changing management practices,

evolution of short duration cultivars, increased cost of cultivation, degradation

of land and water resources, and increasing demands for food in the future,

there is a need to learn how to use available resources efficiently.

The present study was carried out to test the following hypotheses:

i). Productivity of sole sugarcane will be maximum at a lower N level than that

of intercropped cane.

ii). The intercropping system will have higher productivity than the sole

cropping system.

iii). Intercropping will reduce the productivity of sugarcane.

iv). Intercropping will increase canopy cover.

The objectives of the current study were:

i). To determine the response of sugarcane to intercropping with corn and

wheat.

ii). To evaluate the effect of N on sugarcane-corn and sugarcane-wheat

intercropping systems.

iii). To determine the productivity of various cropping systems.

iv). To measure canopy cover in sugarcane sole and intercropping systems.

This research should provide useful information to sugarcane growers

on N fertilization and intercropping of sugarcane.

5

6

CHAPTER II

LITERATURE REVIEW

Sugarcane is one of the major cash crops in many countries of the

world. It is a long duration crop and is quite labor intensive, particularly in

developing countries. Sugarcane is regarded as the most efficient of all

storers of the sun's energy (Ledon and Gonzales, 1950). If the maximum

yield potential of this plant is to be approached, the weather, water, biotic and

soil factors must be optimum. All factors apart from weather are within the

control of man (Chaudhry, 1983). Fertilizer rates used in sugarcane growing

areas of the world vary with N rates ranging from 0 in Florida muck soils to

600 kg ha-1 in soils with high rainfall in Hawaii (Silva, 1989). Soils used for

sugarcane production generally do not supply sufficient N, except for muck

soils. Therefore, N is always applied to sugarcane to obtain maximum yield.

Application of P and K varies with respect to their availability in different soil

types. Cost of fertilizers also affects their application (Silva, 1989).

Recently there have been many changes in different cultural practices

used in sugarcane production, particularly the system used for irrigation. In

Hawaii the growers have shifted from furrow irrigation to drip irrigation, which

has increased the efficiency of irrigation. Studies conducted on intercropping

in different parts of the world have demonstrated higher crop yields and

7

greater efficiency of resource utilization with intercrops than sole crops.

Intercropping studies have also lead to an understanding of the agronomic

and physiological interactions between companion crops that determine

whether the particular crop should be grown in combination or as a pure

stand.

Rationale For Advantages In Intercropping

Multiple cropping is considered more efficient than single cropping with

respect to the use of natural resources such as land, solar energy and farm

inputs. It also minimizes the risk of total crop failure (Willey, 1979; Altieri and

Liebman, 1986; Caldwell and Hansen, 1993). The traditional input of

chemical fertilizers in developing countries is negligible compared to that in

developed countries like the USA. Most of the research in the past has

emphasized cereal/legume intercropping systems and nitrogen economy.

Sugarcane is one of the major crops in many parts of the world that can be

intercropped with legumes or even with cereals. Intercropping has the

potential to increase food and protein production with lower use of costly

inputs. In this situation the research, however, must be directed towards

increasing the efficiency of utilizing the limited resources available.

Farmers in most parts of the world have very small land holdings and

their survival depends on these lands. In such cases growing sugarcane as a

8

monocrop is more risky or may not be profitable. Sugarcane is a long

duration crop. It is planted in wide rows and has slow initial growth and

minimum lateral leaf spread at the early stages of the crop. During this

period, inter-row spaces remain unutilized and weeds grow and compete with

the sugarcane for nutrients, light, and moisture (Yadave, 1982). Whereas,

sugarcane can be grown along with other companion crops of short duration

and with early maturity that can utilize the inter-row space ( Yadave and

Srivastava, 1978).

In many parts of the world, crops like maize (Zea mays L.) and wheat

(Triticum aestivum L.) are staple food crops. These crops are used for food,

fodder for animals and for various industrial purposes. These crops can be

successfully grown with sugarcane as companion crops. This system can

ensure higher returns to the farmers and also provide a source of greater food

production than sole cropping systems.

Many authors after extensive reviews have concluded that the

advantages in intercropping over sole crop systems are typically due to (a)

better utilization of available resources (Andrews and Kassam, 1976; Willey

1979), (b) better weed control due to more competitive plant communities and

species in space and time than sole crops (Listsinger and Moody, 1975; Rao

and Shetty 1977), and (c) better disease and pest control as a result of

species diversity (Baker and Norman, 1975; Finlay, 1974; Raheja, 1977).

Intercropping will have an advantage over sole cropping in the following

situations (Willey, 1979).

1). When intercropping gives full yield of the main crop and some yield of the

second crop. 2). When the combined yield of intercrops exceeds the higher

sole crop yield. 3). When a combined intercrop yield exceeds combined sole

crop yield. The advantage occurs due to spatial and temporal differences in

resource use (complementary effect).

Resource Use

Intercropping can have higher resource use efficiency (RUE) than sole

cropping. The concept of Resource Use efficiency (RUE) was proposed by

Trenbath (1986) to illustrate and quantify the mechanisms that result in this

advantage.

RUE =capture efficiency • conversion efficiency.

= ((RJRo) * (Rat Rj )) * ((B/Ra }*H) Where: ROl Rj , Ra are quantities of

resources potentially available, intercepted and absorbed, respectively, per

unit area integrated over the growing season. B is the whole plant biomass

and H is the harvest index.

Yield Stability

Intercropping predominates in small farms with subsistence agriculture

because it can give greater yield stability than sole cropping. The reason

usually given is that if one crop fails the other can utilize the resources and

9

10

gives the farmer some yield. Investigations on the stability aspects of

intercropping systems have indicated that the advantage of intercropping is

greater under resource limiting conditions (Rao and Willey, 1980).

Diversity

Crop mixtures may result in reduced insect pest attack, restricted

disease and pathogen spread and increased abundance of insect predators.

Altieri and Liebman (1986) explained such behavior with the following

concepts:

Natural enemy hypothesis. Natural predators are more abundant in

the diverse plant population so they reduce the insect population and losses

due to insects in the intercropping system are less.

Resource concentration hypothesis. The herbivore population is

influenced by spatial dispersion of their food plants. Singla and Duhra (1988)

have reported that autumn planted sugarcane intercropped with mustard and

wheat had lower infestation of borer than the sale sugarcane.

Ecological Niche

The yield advantage, especially in traditional intercropping , is an

outcome of the efficient use of resources resulting from different niches and

the distribution of growth factors in space and time. The idea is based on the

fundamental ecological principle that two species can not occupy the same

niche and if they do so, one of them will be excluded from the system.

11

Measurement Of Competition And Intercrop Advantage

Land Equivalent Ratio (LER)

LER has been used extensively for the evaluation of the advantage in

productivity of intercrops in relation to comparable sole crops (Faris et et.,

1982). The concept of land equivalent ratio (LER) is used to determine

whether or not a certain intercrop combination is more productive in relation

to its comparable sole crops (Faris et et., 1982).

In numerical terms LER can be defined as the sum of the fraction of

intercrop yield to that of the sole crop under similar environmental conditions

and management levels.

LER =(Intercrop yield a/sole crop yield a)+ (intercrop yield b/sole crop yield b)

Example: In Sugarcane - Maize intercropping LER will be as follows.

LER = (Intercrop yield of S.cane/Sole crop yield of S.cane) + (Intercrop yield

of Maize/Sole crop yield of Maize)

LER can be: > 1 (intercropping has greater total yields and has an

advantage & is preferable over sole crops)

= 1 (no advantage of intercropping)

< 1 (intercropping has lower total yields than sole crops, sole

cropping is preferable)

LER signifies the amount of land area under sole crops required to

produce the same yields as that produced by one hectare of an intercrop

12

combination. In some cases LER may not be an effective measure of

evaluating intercropping as one crop may generate more profit as a sole crop.

However, economic analysis in such cases may be the better approach to

provide recommendations to farmers.

Relative Crowding Coefficient (Kab) Of A Component

The relative crowding coefficient (Kab) was introduced by de Wit

(1960). The coefficient signifies whether or not the components have

produced more than expected.

Relative crowding coefficient (Kab)= (mixture yield, x proportion of b with a) I

(pure stand yield, - mixture yielda) x proportion of a with b or

Kab=Yab X Zba I (Yaa- Yab) XZab where:Kab =Relative crowding coefficient of crop a intercropped with crop b,

Yab =Yield per unit area of crop a intercropped with crop b (expressed over

the area occupied by both crops),

Yaa = Yield per unit area of sole crop a,

Zba = The proportion of b with a (intercropped area), and

Zab =The proportion of a with b (intercropped area).

The value of Kab can either be:

> 1 (intercrop component a produced more than expected)

=1 (intercrop component a produced equal to expected) and

< 1 (intercrop component a produced less than expected).

13

Aggressivity

The aggressivity index, proposed by McGilchrist (1965), suggests

which intercrop component is dominant and more competitive over the other

one. In mathematical terms this index is expressed as:

Aab= (YatfYaa x Zab) • (YbJYbbX Zba) where Aab (aggressivity of a on b) = 0

signifies that components are equally aggressive and competitive.

Aab=(Actual yield of a when intercropped/Expected yield of a whenintercropped) - (actual yield of b when intercropped / Expected yield of b when

intercropped).

The positive value components will be aggressive and dominant over the

negative value components.

Competitive Ratio (CR)

The competitive ratio (CR) was proposed by Willey and Rao in 1980.

CR is the ratio of two partial LER's adjusted for their proportions in the

mixture.

CRa = ((YatfYaa)/(YbaNbb)) x (ZbiZab) where CRa is the competitive ratio of a

component.

CRa = (LERiLERb) x ZbiZab. This index determines the competitiveness of

one species over the other. CR has been proposed for the evaluation of the

competitive balance between components and the change in competitive

balance in intercrop combinations subject to treatment effects.

14

Intercropping

Intercropping has been a common practice in many parts of the world

even before western agricultural scientists pointed out its technical

advantages over sole cropping. Sole cropping is the main agricultural

practice in almost all agriculturally mechanized countries. Crops like

sugarcane are also grown as a sole crop in these countries. Recent

advances in agricultural research has proved that there is potential of growing

a short duration intercrop in sugarcane without affecting the productivity of the

cane (Mathur, 1980; Rathi and Singh, 1979; Verma et a/., 1981). This idea

has been supported further by many researchers to fulfill the increasing

requirements of food for the increasing world population.

In regions where manual labor is readily and excessively available,

intercropping is a common practice. Sugarcane being a long duration crop is

usually grown in an intercropping system in those areas. Small grains,

legumes, pulses and many other crops provide a nice combination with

sugarcane as intercrops (Mathur, 1980; Rathi and Singh, 1979; Verma et et.,

1981). Kandasami et al., (1977) have observed that intercropping wheat with

sugarcane did not affect the germination and yield of cane. They also found

that there was no significant difference in the sucrose content of cane in

different cropping systems. Growing sugarcane with wheat proved to be more

economical than sole sugarcane or wheat.

15

Reddy (1980) in an experiment where sugarcane was intercropped with

blackgram, cowpeas and wheat, reports that higher intercrop densities

affected the tillering , millable cane and the final yield of sugarcane.

However, lower intercrop densities had no significant effect on the yield and

sugar content of intercropped cane. Juice quality was also not affected by the

intercrops. The intercropping systems proved to be more economical than the

sole crop systems.

Intercropping cane with other crops has also shown that applied

irrigation water is consumed more efficiently by the intercrops than sole crops.

Joshi et al., (1980) conducted a two year experiment with different irrigation

treatments and different sugarcane intercropping systems. Garlic, wheat and

peas were used as intercrops. The results revealed that the effect of depths

of irrigation on cane yield was non significant. In the first year garlic and

wheat depressed cane yield whereas peas as an intercrop in both years and

garlic in the second year had no effect on cane production.

Another study undertaken by Pillay (1980) in Mauritius shows that

intercropped rice had no significant effect on sugar yields. The wide row

spacing (227 cm) proved to be suitable for the rice crop. In the state of Bihar

in India as well as in many areas of Pakistan, sugarcane is planted in two

seasons, that is, spring and autumn. A three-year field trial conducted by

Tiwari et al., (1983), in Bihar, indicates that the highest yield of cane was

16

obtained when cane was planted alone. The second highest yield was

obtained in the cane-mung intercropping system. Although depression in

cane yield due to intercropping was common, still the highest returns were

obtained from the intercropped cane.

In the semi-arid areas of northeastern Brazil, intercropping is the

predominant farming system. Experiments in Brazil have shown that a

sorghum-pulse (cowpeas or common beans) intercropping system yielded

more grain than the monocrop system and produced a land equivalent ratio

(LER) greater than 1.00, even though rainfall was limited. The two crops in

the intercrop system were responsive to fertilizer application. These results

have been reported by Faris ef a/., (1983).

Autumn planted sugarcane with a suitable companion crop is an

economically feasible cropping system for better crop production and juice

quality. Potato, wheat, mustard, coriander and tobacco can be raised

successfully in sugarcane without any disadvantage to the cane crop (Mathur,

1980; Rathi and Singh, 1979; Verma, et a/., 1981). Intercropping also

provides a diverse environment where the chances of disease incidence are

lower than in pure stands. Singh et a/., (1983) observed that wilt incidence of

sugarcane was lower when sugarcane was grown with coriander, rye and

wheat, than in pure stand.

17

Intercropping in sugarcane is a very common practice in the Sind

province and parts of Punjab in Pakistan. Solangi and Udhejo (1985)

conducted a two year experiment on intercropping maize, mung, sunflower,

soybeans, clovers, lentils, garlic and onion with sugarcane. Intercropping

reduced cane yield, growth and tillering. However, intercropping maize and

onions proved economical and gave higher net returns than the other

intercropping systems. Agarwal and Shukla (1987) included four legumes

(cowpea, urd, mung and sunhemp) in a sugarcane intercropping study. A

drop in pH was observed during the tillering phase of sugarcane. Soil organic

carbon increased significantly. The maximum number of tillers was produced

when sugarcane was planted with cowpeas.

Kapur et a/., (1988) evaluated the performance of varietal mixtures of

sugarcane and reported an increase in the yield of cane and sugar up to 25 %

in mixtures than in pure stands. The number of millable canes, sucrose

contents and cane yield in mixtures was more stable than in pure varieties.

Opportunities exist for intercropping different crops in sugarcane and

medicinal plants are promising intercrops for sugarcane. Sharma et al.,

(1989) in a sugarcane intercropping study, planted mint as a double row

intercrop. Although this system affected cane yield, intercropping mint in

sugarcane gave the highest net return. Intercropping of a single row of mint

in sugarcane did not affect sugarcane yield.

18

Rao and Singh (1990), in a productivity and risk evaluation study in

different intercropping systems, found that the productivity of most of the

intercropping systems was closely related to the diversity of the crops

involved. Intercropping systems showed a larger and consistent advantage

over the respective sale crop systems. In the economic terms intercrops were

more profitable than sole crops.

Potato has been grown in Mauritius on a small scale for over a century.

The bulk of the potato (77 % of the total) is produced on sugarcane land. On

the basis of the total edible energy production, intercropping of potato is

estimated to be more productive than sale cane by 22 %. The Land

Equivalent Ratio of the system is estimated to be more than 1.17, on average.

Sugarcane growers derive as much as 63 % more net returns from

intercropping sugarcane with potato than sale sugarcane (Govinden, 1990).

In Bangladesh sugarcane is grown mostly under rainfed conditions,

planted as a winter or a spring crop with a duration of one year. Imam et al.,

(1990), from a series of thirteen experiments, observed that cane yield was

enhanced when intercropped with potato and benefit was related to the use of

residual P and K and to a lesser extent N. In all experiments returns from

cane intercropped with potato were greater than from sale cane and were

further increased by the use of mulch. Nankar (1990), in different

experiments, concluded that intercropping potato with sugarcane did not

19

adversely affect the sugarcane yields. Yield of intercropped potato

responded to the higher plant densities. Net returns from intercropping were

higher than that of sale sugarcane.

Sawhney et et., (1991) carried out a two-year intercropping study in

sugarcane. Mung was planted as an intercrop in the spring planted

sugarcane. Planting geometry was one of the treatments. Intercropping of

two rows of mungbeans in sugarcane rows 90 cm apart gave the highest

intercrop yield. Intercropping did not affect the growth and productivity of the

sugarcane crop. LER (Land Equivalent Ratio) values of 1.58 in 1987 and

1.88 in 1988 were observed. In another study in India, companion cropping of

sugarcane with carrots and turnips also demonstrated that companion

cropping produced higher total yields than sole crops (Mehra et al., 1992).

Net returns were higher in the companion crops than the sale crop systems.

Nitrogen

Nitrogen is regarded as the most influential plant nutrient in the

regulation of sugarcane growth and production (Clements, 1980). Nitrate and

ammonium are the major sources of nitrogen taken up by plants. Most of the

ammonium is incorporated into organic compounds in the roots, whereas

nitrate is mobile in the xylem and can also be stored in the vacuoles of roots,

shoots, and storage organs (Marschner, 1986). Most soil nitrogen occurs in

20

organic forms in the soil solids. A small amount of organic nitrogen is found

in the soil solution, but plants are not known to take up any significant part of

it, and must depend upon the inorganic forms that are released when

microorganisms decompose organic compounds (Black, 1993).

Depending on the plant species, development stage, and organ, the

nitrogen content required for optimal growth varies between 2 and 5% of the

plant dry weight. When the N supply is suboptimal, growth is retarded;

nitrogen is mobilized in mature leaves and retranslocated to areas of new

growth. Typical nitrogen deficiency symptoms, such as enhanced

senescence of older leaves, can be seen. An increase in the nitrogen supply

not only delays leaf senescence and stimulates growth but also changes plant

morphology in a typical manner, particularly if nitrogen availability is high in

the rooting medium during early growth. Shoot elongation is enhanced and

root elongation is inhibited, a shift which is unfavorable for nutrient acquisition

and water uptake in later stages. The length, width and area of the leaf

blades increase, but the thickness decreases. In addition, the leaves become

increasingly droopy, an effect that interferes with light interception

(Marschner, 1986).

Sugarcane is more responsive to nitrogen application than many other

annual crops. Promising varieties of sugarcane differ considerably in their

nitrogen requirements (Zende, 1973). The same variety grown in different

21

environments and soil responded to nitrogen differently at various applied N

rates. Humbert (1963) stressed the importance of optimizing nitrogen levels,

since inadequate N rates result in lower yields, while excessive rates result in

the deterioration of the quality of juice. Studies also show that N uptake is

regulated by plant nitrogen requirements during the growth of sugarcane

(Jaswal and Singh, 1974).

Barnal (1977) recommended an application of 120 to 240 kg N ha" in

different soils of Mexico. He also observed that application of N affected the

sucrose accumulation in different soils. Chui and Samuel (1977) observed

significant increases in cane and sugar yields with 90 kg N ha". Sucrose

percentage in cane was not significantly depressed in this case. In Peru, the

majority of sugarcane is cultivated in the arid coastal valleys, where the

industry has developed. However, sugarcane is also cultivated on a small

scale in some valleys of the sierra and forest. Saldarriaga ef aI., (1977) in a

study indicated that sugarcane responded significantly to increasing nitrogen

levels. The maximum cane and recoverable sugar yields were achieved with

the application of 423 and 378 kg N ha", respectively, in cane harvested at 21

months of age.

Lal and Lal (1978) reported that N application to sugarcane improved

millable cane population but did not affect percent commercial cane sugar.

Application of 325 kg N ha' increased cane yield significantly but did not

22

affect juice quality. A study of nitrogen and irrigation response of two cane

varieties was conducted at the Sugarcane research institute, Faisalabad,

Pakistan. The study revealed that zero nitrogen reduced tillering while

increasing nitrogen levels improved tillering. The larger N application

ensured better growth and increased yield by improving cane height (Fasihi

and Malik, 1980).

Ratooning of sugarcane is a universal practice for economic reasons.

One ratoon following the plant crop is common practice in the Philippines.

Gotera et al., (1980) observed that nitrogen applied to the ratoon crop is the

major factor in increasing the tonnage of cane. The availability of adequate

moisture is one of the important factors in improving nitrogen uptake and cane

productivity. A sugarcane variety by N study in plant and ratoon cane, was

carried out in India (Yadave 1983). Increasing N application increased cane

yield in the ratoon as well as in the plant cane. Application of 100 kg N ha"

gave the maximum response at 225 kg residual N ha-1• Application of N to the

ratoon crop directly or indirectly decreased the sugar content in juice.

Stalk height and number of tillers are important characteristics

contributing to the final cane yield. Inman-Bamber (1984) in a cultivar and N

study found that application of N increased cane yield while the sucrose

contents decreased with applied N. Application of nitrogen markedly

increased stalk height and number of tillers before closure of the canopy.

23

However, the number of tillers declined after closure because some of them

died due to lack of light and competition with the strong stalks. Stalk height

increased significantly during the first six months of growth. Inman-Bamber

also found that the effect of N on stalk height was reduced at harvest. About

60 % of the stalks flowered in those plots where no nitrogen was applied.

Each increment of 50 kg N ha" reduced flowering and in plots, receiving 150

kg N ha", only 10 % of the stalks flowered.

Parasad et et., (1985) concluded that 117 kg N ha", 71 kg P20S ha"

and 11 kg K20 ha" was an economical fertilizer application for sugarcane in

calcareous soils of Bihar, India. The effect of N on the yield of autumn cane

and sugar of new cane cultivars was studied in Taiwan during 1985-86. It

was found that cane yield and sugar yield decreased with the overuse of

nitrogen (Taiwan Sugar Research Institute, 1985-86). Singh and Ali (1986)

observed that plant height and number of millable canes increased

significantly with the application of nitrogen. Increasing doses of nitrogen up

to 180 kg ha" generally increased the height, number of tillers and millable

canes.

Santo and Meinzer (1986) used N rates up to 1086 kg ha" and

concluded that application of 265 kg N ha" gave maximum yield in sugarcane.

Sharma et al., (1987) reported that nitrogen application produced higher

numbers of stalks and yield. Ali et al., (1987) compared the effect of foliar

24

and soil application of nitrogen to sugarcane and found that irrespective of the

mode of application, increasing nitrogen application increased cane yield.

Abayomi (1987) recorded a significant effect of nitrogen on the fresh and dry

weight of shoots. The lowest weights were obtained at 0 nitrogen while the

highest weights were recorded at 160 kg N ha". The number of millable

stalks at harvest showed a similar response. However, the highest number of

millable stalks was recorded at 120 kg N ha",

Panwar et al., (1987) and Dhiphale et el., (1988) reported maximum

ratoon cane yield at 225 kg N ha". Iruthayaraj and Rangasamy (1988)

regarded the application of 275 kg N ha", 62.5 kg phosphorous, and 225 kg

Potash ha" as the fertilizer combination that gave higher cane yield. Anders

(1988) reported that application of 364 kg N ha" produced maximum dry

matter. Nitrogen in stalks also increased with increasing rates of applied

nitrogen. Sugar quality and plant stalk population were not affected by N

levels and irrigation.

Srivastava and Dixit (1988) found that application of 150 kg N ha"

increased the sucrose contents of juice compared to the control. Durai et al.,

(1989) investigated the effect of different levels of N and time of application

on plant and ratoon cane and found that application of 325 kg N ha' in three

doses produced maximum millable cane in the plant crop. While application

of 275 kg N ha' in three doses produced higher cane yields in the ratoon

25

crop. The study further showed that the quality of juice was not affected by N

application. Jeyabal et aI., (1989) recommended the application of 250 kg N

ha" to obtain maximum cane yield. Sugarcane being a long duration crop

requires higher amounts of nutrients and water for maximum productivity.

Siag et al., (1989) found significant differences in cane yield of both plant and

ratoon cane due to irrigation and nitrogen levels. Application of 200 kg N ha"

produced maximum cane yield but the quality of cane juice deteriorated when

nitrogen levels exceeded 150 kg ha",

In another study in Taiwan, fifteen field trials on nitrogen fertilization

were conducted at seven locations. The study revealed that the effect of N

fertilizer on sugar yield varied with the amount of N applied, planting time of

cane, and location. No significant increase in sugar yield was observed with

additional nitrogen when the rate of N exceeded 200 kg ha". N application of

300 kg ha" resulted in a reduction of sugar content (Taiwan Sugar research

Institute, 1990-1991). Yadav ef al., (1990) observed that N application

produced significantly taller and thicker stalks in plant and ratoon cane

resulting in higher cane yields. Application of N to previously unfertilized

sugarcane ratoon plots produced a yield increase of 27.6 T ha". The direct

effect of N application in the ratoon crop was 184 kg of cane per kg applied

nitrogen.

26

In the sugarcane industry press mud is a major by-product and may be

derived from the sulphitation or carbonation processes used to remove

impurities from cane juice. Sulphitation mud or filter cake is well known for its

use in the reclamation of alkaline soils (Kanwar and Chawla, 1963). In an

experiment Yaduvanshi and Yadav (1990) observed that application of 150 kg

N ha" increased cane biomass by 24.6 % and application of 30 T ha-1 press

mud by 38.1 % over the control. Whereas, the combination of the two

increased cane biomass up to 38.1 % over the control. Sulphitation press

mud enhanced the availability of Nand P to the crop and reduced soil pH.

The extent of tillering and their survival to millable stalks is a varietal

character but is also influenced by other factors such as fertilizer application

and moisture management (Raheja and Singh, 1952). The number of millable

canes produced per unit area is one of the important characters that

determines the yield of sugarcane (James, 1971).

Lal (1991) observed that application of 225 kg N ha" produced more

tillers than the control. The yield of sugarcane was significantly influenced by

higher moisture regimes and increasing rate of nitrogen. In another study, Lal

(1991) observed that LAI and dry matter production of sugarcane were

significantly higher with the proper moisture regimes and higher nitrogen

levels. Chalapathi (1991), in a study on the effect of fertilizer on sugarcane

yield, found that the application of 250-75-75 NPK kg ha" produced higher

27

cane yields and the increase in nitrogen level from 250 to 300 kg N ha-1 had

no positive effect on cane yield. Kumaraswamy and Rajasekaran (1992)

conducted a study on the response of sugarcane to nitrogen and potassium

and reported that the crop responded significantly to N application up to 280

kg ha". The maximum economic yield of the ratoon crop was obtained with

210 kg N ha". Commercial cane sugar (CCS) was not affected by the higher

nitrogen levels. The N concentration of the leaf blade and stalks increased

with increasing application of nitrogen.

Crops may suffer from damage due to lodging at various times from

anthesis until harvesting. Cultivar, sowing date, nitrogen fertilization and

plant growth regulators are crop management factors involved in determining

lodging. White (1991) studied the response of winter barley cultivars to

nitrogen and a plant growth regulator in relation to lodging. Nitrogen

application increased plant height but did not affect dry weight. The growth

regulator treatment however reduced plant height and did not decrease dry

weight significantly.

Maskina et al., (1993) studied the residual effects of N on no-till corn

production and N uptake of 0, 50, 100, and 150 % of the amount of crop

residues produced by the previous crop during the previous five years. The

effects were evaluated with and without tillage, N fertilizer (60 kg ha"), and

hairy vetch. The results revealed that growth and N uptake by corn generally

28

increased as previous residue rate increased. The higher crop residues

produced more organic C, and total nitrogen, particularly in the upper 30 cm

layer of soil.

Stecker et et., (1993) conducted a study at three different sites during

1989-90 to evaluate the effect of different sources of nitrogen and rates of

application (67,135, and 202 kg N ha") in a corn following corn and corn

following soybean pattern. Nitrogen sources and rates affected the yield at

each site. Grain yield for ammonium nitrate was highest among the other

sources, averaged across the sites and years. Grain yield response to

applied nitrogen were greater with continuous corn than corn following

soybean.

In another study, Stecker et al., (1993) evaluated the effect of different

application methods of N on the productivity of no-till corn. Knife, dribble and

broadcast methods at 67, 135 and 202 kg N ha-1 were studied. Nitrogen

losses were minimum with the knife injection method compared to the others

and corn responded well to the available nitrogen. Yields were 4 to 20 %

higher with this method compared to the other application methods. Grain

yield in the dribbled and broadcast method was similar.

Varshney et al., (1993) conducted a study to determine the effects of

tillage and nitrogen management on the residual nitrate nitrogen using corn

as the target crop. N was applied as a single dose of 175 kg ha" or three

29

doses totalling 125 kg N ha-1 for continuous corn production. No till and three

N applications reduced the residual nitrate N in the soil profile. Corn yields

were, however, not affected by the N management methods or by tillage as

corn responded to N in all cases. Quantification of plant root branching,

particularly under water stress, is important for evaluating the contribution of

plant roots to water and nutrient uptake and subsequently to plant growth.

Eghball et et., (1993) carried out an experiment to study the roots fractal

dimensions as altered by N stress, using different corn genotypes. The

results of the experiment indicate that root abundance was lowest for zero N.

The amount of roots in the section below the crown was 45 % of the total

roots. Nitrogen stress changed the morphology of the corn root system and

caused less root branching.

Corn plants grown under higher nitrogen fertility have a higher protein

concentration. Zhang et al., (1993) conducted a field study at four locations

to evaluate the effect of N fertilizer source, application rate and application

time on the yield and quality of corn. They found that grain yield of corn

increased with increasing N fertilizer rates and was generally not significantly

affected by the number of the N applications. Neither corn yield nor corn

quality were affected by the different N sources. Sanders ef el., (1993)

evaluated the effect of different previous crops, planting densities and N

application on the uptake of N by different vegetable crop sequences. The

30

results indicated that higher plant densities resulted in higher per hectare N

uptake whereas N uptake by individual plants at low densities was higher than

by plants at higher densities. Metzger (1993) in an experiment evaluating

different fertilizer combinations, observed that higher amounts of Nand K

resulted in delayed maturity of corn, excessive husk growth, and multiple ear

production.

Intercropping And Nitrogen

Results from many intercropping studies have shown the advantage of

intercropping over sole cropping in terms of its efficiency of using and

conserving natural resources and producing higher net returns. In most

cases legumes have been used as the intercrop with non-legumes. Ahmed

and Gunasena (1979) used 0, 60 and 120 kg N ha" and reported that yields

of cowpeas intercropped with maize were depressed by larger N applications.

On the contrary, Karla and Gangwar (1980), in India, found that both 80 and

120 kg N ha-1 gave larger cowpea seed yield than 40 kg N ha". Legumes can

contribute an apparent associative benefit of N excretion to the companion

non-legume crop (Eaglesham et al., 1981).

Yadave (1981) studied the residual effects of N from a maize-

pigeonpea intercrop on the subsequent sugarcane crop. Nodulation of the

pigeonpea increased N content of the soil but did not contribute to maize

31

yield. However, sugarcane yield increased by 43 % when grown in the same

field after the maize-pigeonpea intercrops. Yadave (1982) also concluded

that sugarcane intercropping with legumes is more profitable than a sole

sugarcane crop because it gives higher net profits and higher LER. Gangwar

and Karla (1982) carried out a study on the response of maize to

intercropping and nitrogen in the rainy season. The results of the experiment

showed that the average increase of total grain production by intercropping

ranged from 29.5 to 92.5 % over a pure stand of maize. Intercropping gave

higher net returns and application of 80-120 kg N ha" increased the total

production by 29.0 to 37.5 % over that from 40 kg N ha", Application of 80 kg

N ha-1 proved to be more economical in this study.

Planting soybean before sugarcane or phaseolus beans in sugarcane

increased soil N without harming sugarcane yield and produced additional

yield of the companion sugarcane crop. This increase in soil N resulted from

the ability of legumes to fix atmospheric nitrogen and thus benefitting the

companion crop (Ruschel and Vos,1982).

Bains et a/., (1984), in an intercropping study of sugarcane and

sugarbeet, found that the yields of the intercrops were higher than those of

sole crops. The lower N level of 60 kg ha·1 was found to be comparable to the

higher N levels of 90 and 120 kg ha" in beet root yields. The juice quality of

beet roots, as reflected by percent pol, decreased with increasing levels of

32

nitrogen. Net returns and LER were higher in a sugarcane-sugarbeet

intercrop, with an N rate of 120 to 150 kg ha" and maximum net return was

37 % more than that of sugarcane sole crop (Singh and Singh, 1985). Singh

and Rathi (1985) conducted a study on the nitrogen needs of potato and

mustard intercrops in autumn planted sugarcane. The results revealed that

the tuber yield was higher in the intercropped potato than the sole crop

potatoes. The nitrogen requirements of the intercrop was 18 % lower than

that of the sole crop. Intercropping of potato and mustard with sugarcane

proved to be more beneficial than planting sole cane after potatoes and

mustard. The profitability of intercropped cane was 48.58 % higher than that

of sole cane.

Agarwal et a/" (1986) reported that intercropping sugarcane with

cowpeas and moong reduced the yield of sugarcane in general but applying

nitrogen to intercropped sugarcane improved cane yield. Intercropping

pulses in sugarcane increased organic C, total N, and available P contents of

the soil (Yadave et al., 1987). An increase in N rates, increased cane

production and total N uptake by intercropped sugarcane. Kapur and Kanwar

(1987) conducted a nitrogen application by timing study in a sugarcane and

sugarbeet intercropping system and found that intercropping sugarbeet with

cane decreased the yield of sugarcane from 10.16 to 34.6 % from sole cane.

The significant yield increase in sale cane over intercropped cane was

33

attributed to the higher tiller production that resulted in more millable cane.

The treatment had no significant effect on the sucrose content of juice. The

sucrose content of intercropped cane was higher than that of sole sugarcane.

The observed results are similar to the findings of Kumar ef al., (1980).

Verma and Yadave (1988 a) observed that the response of sugarcane

to N with different companion crops is different. According to their

observations a potato-sugarcane intercrop required less N than a wheat,

coriander or mustard-sugarcane intercrop. Similar results have been reported

by Verma ef al., (1985). Sugarcane intercropped with wheat produced an

additional 4.8 T ha" of wheat yield along with the sugarcane yield that was

same as in the sole crop. LER was also higher in intercrops than in the sole

crop with a nitrogen dose of 200 kg ha" compared with 150 kg ha" (Verma

and Yadave, 1988 b).

Kapur and Kanwar (1989) carried out a study on the nitrogen

requirements of different sugarcane intercropping systems. Sugarcane was

grown with wheat or raya (Brassica family oil seed crop) or sugarbeet.

Different nitrogen levels were used as the main plot treatment. Cane yields

as well as commercial cane sugar yield increased significantly up to 260 kg N

ha". The increase in number of tillers with N application, resulted in a higher

number of millable canes, that resulted in higher cane yields. N levels above

260 kg ha' caused lodging of the cane and ultimately resulted in lower cane

34

yields. Juice quality was not affected by N application or by the intercrops.

Intercrops also did not affect the number of millable canes, number of tillers,

and plant height. Kanwar et a/., (1987) reported similar observations in their

study. In a rice-pigeonpea intercrop, N uptake by rice grain and straw

increased progressively with increasing levels of Nand inspite of the higher

cost of cultivation in intercropping, it gave higher gross and net returns than

sole crop rice (Mahapatra et al., 1990).

Soil Erosion And Intercropping

Soil erosion is a function of factors such as climate, topography,

vegetation, soil characteristics, soil use, and human activity (Hudson, 1971).

Based on data from EI-Swaify and Dangler (1982), soil/osses in Asia are the

highest (166 T km2 year") followed by those in South America (63 T km2

year"). River borne sediments, caused by erosion, carried to the ocean

increased from 10 billion tonnes per year, before the introduction of intensive

agriculture, grazing and other activities, to between 25 and 50 billion tonnes

per year thereafter. High rainfall and sloping lands in these areas are major

contributors to soil losses (Lal, 1990).

Many tropical areas receive more than 2500 mm rainfall per year with

substantial rainfall every month (EI-Swaify et al., 1982). Soil losses are

35

usually high (EI-Sawify et et., 1982) from water erosion under the following

conditions:

1. High intensity and long duration of rainfall.

2. High rates of overland flow from adjacent upland.

3. Poorly structured soil with low infiltration rate.

-4. Slope with high or moderate steepness.

5. Long slopes.

6. Tillage and planting in rows directed with, rather than across,

the prevailing slope.

7. Absence or sparse vegetative cover, with insufficient protective

organic residue.

Unprotected soil will lack physical binding by plant stems and roots.

The infiltration rate and faunal and biological activity will be lower in such

soils. Bare soil is likely to have low organic matter content resulting in poor

soil structure and water holding capacity (Stocking, 1988).

Land use is another important factor contributing to either soil loss or

soil conservation. Farmers who try to achieve high productivity by improving

crop health also produce better crop cover, root development and vegetative

growth. This provides more crop residue which gives better coverage to the

soil leading to more infiltration and available water with less runoff and

improved stream flow (Shaxon et al., 1989).

36

The continuously increasing population of the world and shrinkage of

land resources clearly indicate that the impact of soil erosion on productivity

should be given foremost importance particularly in developing countries (EI-

Swaify ef al., 1982). According to Shaxson ef al., (1989), the following steps

are appropriate for practicing soil conservation on steep lands.

1. Manage rainfall, then runoff.

2. Improve soil cover.

3. Improve soil structure and rooting conditions.

4. Catch the rain water where it falls.

5. Increase soil moisture; and

6. Increase organic activity in soil.

Appropriate cropping systems (crop combinations and rotations) or

agroforestry systems that involve growing annuals in association with

perennials during the initial stages of tree crop establishment, and planting

appropriate pasture species will help to achieve the first three steps (Lal,

1990).

Maintaining adequate soil cover is considered to be the best means of

minimizing or preventing soil erosion (EI-Swaify ef al., 1982). For example, at

Dehra Dun, in North India, soil losses of 42 T ha" under 1250 mm rainfall on

bare fallow were reduced to 1 T ha" by natural grass cover (Patnaik, 1975).

Cover crops, besides protecting soil against erosion, also smother weeds that

37

may be incorporated into the soil as green manure. The efficiency of cover

crops is related to characteristics such as density of foliage, root growth

characteristics, water retention, depletion and penetration and soil fertility (EI-

Swaify et a/., 1982). In a study conducted by Georges (1977) soil erosion on

hilly lands of Trinidad in sugarcane fields was measured. A comparison of

soil loss was made in cane planted fields and bare fields. The results indicate

that there was considerable reduction of erosion under the cover of plant

cane than from bare soil. Georges (1977) concluded that a substantial

reduction in soil loss could be achieved by early planting of sugarcane that

will provide early cover to the soil.

The use of legumes as ground covers reduced runoff and soil loss from

maize (EI-Swaify et al., 1988). Similar beneficial effects were also gained

from legume intercropping with cassava. Besides providing protection against

runoff and erosion, legume intercrops also resulted in yield gains in

succeeding crops due to nutritional contributions from their residues and also

added income in the case of groundnut.

Many interactive processes between a plant and the soil affect

erosion. Some of these processes are:

-Physical binding of soil by plant stems and roots.

-Electrochemical and nutrient bonding between soil and roots.

-Detention of runoff by stalks and organic litter.

38

-Improved infiltration along root channels.

-Greater incorporation of organic matter into the soil, resulting in better

structural and water holding qualities.

-Increased faunal and biological activity, leading to better soil structure

(Stocking, 1988).

The Universal Soil Loss Equation (USLE) is now the most widely used

model for predicting sheet (interrill) and rill erosion (Wischmeier and Smith,

1978). The plant C factor is an important part of the universal soil loss

equation (USLE) and can be used to predict soil losses.

Based on data from over 25 years of research, from which the rainfall

parameter was modified and the soil susceptibility to erosion (erodibility

factor) quantified, the universal soil loss equation ( USLE ) for predicting

sheet and rill erosion was proposed (Wischmeier and Smith 1961, 1965 ).

USLE has the following form:

A =R K L S C P (Where A is soil loss)

It identifies six important parameters as most influential in rill and

interriil soil erosion caused by water. These parameters are rainfall erosivity

(R), soil erodibility (K), cropping management (C), erosion control practice (P)

and two topographic factors - slope length (L) and steepness of slope (S).

Other factors being constant, rainfall erosion from vegetated soil is

determined by crop type, planting density, canopy characteristics, growth

39

habits and quality of stand. A healthy canopy cover serves as a rainfall

interceptor and dissipates the kinetic energy of the raindrops, increases

infiltration, reduces runoff, and binds soil by root action.

Factors such as K, have a/ready been defined by several researchers

with rainfall simulator data (Dangler et al., 1976, EI-Swaify et al., 1982,

Dangler and EI-Swaify, 1976). Rainfall erosivity or the rainfall erosion index

involves the total kinetic energy (E) of the test storm times its maximum 30

minute intensity. The USLE topographic factor (LS) is calculated from the

length and slope of the landscape profile. Rainfall erosivity EI30 is calculated

for different rainfall storms for each month.

EI30 =KE of the storm x 130KE =916 + 331 10910 I, where I is rainfall intensity per hour.

Soil loss ratio (SLR) can be calculated by assuming 1 with bare soil

and 0 with 100 % canopy cover. The soil loss ratio is estimated from the

percent cover. The plant C factor is calculated as follows:

Incremental C value =EI x SLR

Where EI is soil erosivity (R) and SLR is soil loss ratio.

Annual average C value =Sum of incremental C 1# of years

Incremental C is calculated for different crop growth stages in sole

crops starting from bare fallow. Crop growth stages are as follows:

Growth stage

F

sa

Description

fallow, rough due to primary tillage

from end of fallow to secondary tillage, seed bed

40

condition + end of sowing and 10 % cover

1 10 % to 50 % canopy

2 50 % to 75 % canopy

3 maturity to 100 % canopy

4 after harvest, stubble, residue, until primary tillage.

With the calculation of earlier stated parameters, soil loss in qualitative

terms can be determined by the use of USLE.

Crop Residue Cover

Conservation cropping systems also include the management of

surface residue to control soil losses due to wind and water erosion (Morison

ef al., 1993). Correct and valid measurements of the percentage of soil

surface covered by crop residues are very important in soil management in

order to reduce soil losses by erosion. Crop residues used to be quantified in

terms of their dry weight until the soil conservationists learned and realized

that soil cover by crop residues provides better correlation with erosion

control rather than the dry weight of the residues (Gilley ef al., 1986).

41

Crop residue cover is determined by different methods. These

methods include the line-transect method (Sloneker and Moldenhaur, 1977),

the dot screen method (Morrison et a/., 1989), a meter stick method (Hartwing

and Laflen, 1978), the slide photographic technique and projection of

photographs on dot screens, video image analysis (Meyer et al., 1988) and

residue meters (McMurtrey et al., 1993).

As stated earlier, multiple cropping is considered highly productive and

also helps reduce soil erosion on small farms. It includes sequential cropping

that limits the bare fallow time between crops, or inter-row cropping that limits

the spatial extent of bare soil within a field. Use of multiple cropping systems

can increase farm productivity and income.

42

CHAPTER III

MATERIALS AND METHODS

Location and Field Plan

The experiment was conducted on the University of Hawaii's

Agricultural Research Station at Waimanalo, Oahu, on a Wailua, gravely clay

variant (Vertic Haplustoll, very-fine, kaolinitic, isohyperthemic). Annual

rainfall at the site ranges from 657 to 1270 millimeters and falls mainly

between November and April (Ikawa et a/., 1985). The experimental plan

included four (4) nitrogen levels (0,75, 150 and 300 kg ha"), five (5) cropping

systems (two intercrop and three sale crop systems) and four (4) replicates.

Sugarcane was the main crop that was planted with two other crops, sweet

corn and wheat. There were also sale crop plots for each crop. A split plot

design was used with cropping pattern as the main plot and N levels as the

sub-plots.

Sweet corn was planted before the installation of the experiment to

deplete nitrogen from the field and was harvested at the soft dough stage of

the grain. The land was plowed with a mold board plow and was disked. The

experiment was installed on May 11, 1993. Irrigation water was applied

through a sprinkler irrigation system initially and later through a drip irrigation

system starting on September 09, 1993 up to the final harvest of sugarcane.

43

Cropping Patterns

i) Sugarcane sale crop.

ii) Sweet Corn sale crop.

iii) Wheat sale crop.

iv) Sugarcane - Sweet Corn intercropping system.

vi) Sugarcane - Wheat intercropping system.

The plot layout is described below:

Sole Crop Plots

Sugarcane (Saccharum officinarum L.) cultivar 74-4527 (from the

Hawaiian Sugar Planters Association) was planted in a single row pattern.

Sugarcane seed pieces, eighteen (18) inches long with 2 to 3 nodes, were

used for planting. The seed pieces were placed end to end in the rows. Row

spacing was 1.5 m between rows. Each treatment plot consisted of four

sugarcane rows with the middle two rows used for data collection. The main

plot, including border rows, was 23 x 6 m. This main plot was divided into

four sub-plots for N treatments. The first and the last sub-plots in the main

plots measured 5.5 x 6 m whereas the central sub-plots were 6 x 6 m each.

Larger border areas were kept between the middle plots to prevent the N

moving from one plot to another and this resulted in larger plots in the middle

than on the ends of main plots.

44

Sweet corn (Zea mays) variety Super Sweet #10 was planted at a row

spacing of 0.75 m between rows. Plant to plant spacing was 22.5 cm. Four

rows of corn were planted. The two middle rows were used for data collection

and the two outer rows were used as border rows. The main plot for corn was

23 x 2.68 m and was divided into four sub-plots for N treatments. The two

sub-plots on each end of the main plot were 5.5 x 2.68 m and those in the

middle were 6 x 2.68 m.

In the case of wheat (Triticum aestivum L.), variety Norstar (from

Alberta Canada) was used. Eleven (11) rows were planted at a row spacing

of 0.20 m between rows. Five (5) middle rows were used for data collection

while three rows were used as borders on each side of the plot. The main

plot size was 23 x 2.2 m. The main plot was divided into four sub-plots for N

levels. Individual plots on either end of the main plot were 5.5 x 2.20 m and

plots in the center were 6 x 2.20 m.

Intercrop Plots

Sugarcane - Sweet Corn. In the sugarcane-sweet corn intercropping

pattern, two (2) maize rows were planted between the sugarcane rows at a

row spacing of 0.50 m. Sugarcane was planted as described for the sale

crop. The main plot size was 23 x 6 m while the sub-plot size, for the four N

treatments, was similar to that of the sale sugarcane plot (5.5 x 6.0 m at both

ends of main plot and 6.0 x 6.0 m in the middle of the main plot). Sugarcane

45

harvest rows were the same as in the sale crop. Sweet corn harvest rows

were the two (2) rows between the sugarcane harvest rows.

Sugarcane - Wheat. Five rows of wheat were planted between the

sugarcane rows at a row spacing of 0.20 m. The sugarcane planting pattern

was similar to that of the sale crop. The main plot was 23 x 6 m while the size

of individual sub-plots was similar to those of the sugarcane sale crop system

(5.5 x 6.0 m at both ends of main plot and 6.0 x 6.0 m in the middle of the

main plot). Sugarcane harvest rows were similar to those of the sale crop plot

while wheat harvest rows were the five (5) rows in between the sugarcane

harvest rows.

Fertilizer Application

Nitrogen was applied at the rate of 0, 75, 150 and 300 kg/ha in three

equal doses by broadcast application at planting and by banding on either

side of the rows in later applications. The second dose was applied at 42

days after planting (DAP). The third dose was applied at 56 DAP to all sweet

corn, at 81 days after planting to all wheat and 151 DAP to all sugarcane.

Phosphorus was applied at the rate of 30 kg ha' as TSP (Triple super

phosphate) by the broadcast method at planting and was incorporated into

the soil. Zinc was applied at the rate of 15 kg ha" as Zinc Sulphate and

46

Copper at the rate of 10 kg ha" as Copper Sulphate at the time of planting

and was incorporated into the soil.

Field Maintenance

Land preparation and Irrigation were kept uniform for all treatments.

Weeds were controlled by the application of herbicides. A mixture of Atrazine

and Lasso, at the rate of 3.4 kg. a.i. (active ingredient) each per hectare, was

sprayed as a pre-emergence herbicide to control weeds in sugarcane and

sweet corn. Weedar 64 was applied to the wheat crop at 28 days after

planting. The second application of herbicides (Atrazine and Ametryn at the

rate of 3.4 kg. a.i. hectare" each) to sugarcane was given at 98 days after

planting.

Data Collection and Sampling

Soil Analysis

Fifteen (15) soil samples to a depth of 45 cm were collected from the

experimental site prior to the planting of sweet corn for N depletion. These

fifteen soil samples were composited to give five (5) samples for analysis.

The soil samples were analyzed for nutrients to determine the amounts of

phosphorous, potassium and other micronutrients to be applied before

planting (Appendix 3.1).

--------- .--- ----

47

Crop Residue

Data on initial crop residue, before the installation of the experiment,

were collected with the following procedure:

Just before plowing, 10 sampling areas of 1 m2 each were randomly

selected in the experimental area. The above ground residue was collected

from each sampling area and fresh weight of the sample was recorded in the

field. Average fresh weight of the samples was determined. A sub-sample of

200 grams was taken from each sample and oven dried at 70° C until a

constant dry weight was obtained. Average moisture content (M.e.) of each

sub-sample was determined with the following formula:

M.C = (Fresh weight - Dry weight) / Fresh weight

The amount of residue was expressed in kg na', on the dry weight basis by

the following equation:

Crop Residue (kg ha") =(average fresh weight m2)(1-average M.e.)(10,OOO)

(IBSNAT, 1990)

Weather Data

Average daily rainfall, maximum, minimum and average daily

temperature and solar radiation were recorded daily. These data were

recorded from the weather station already installed at the Waimanalo

Experimental Farm. Rainfall was recorded with an automatic tipping bucket

while air temperature was recorded with thermocouple sensors. Solar

48

radiation was recorded with a Licor sensor having a silicon cell pyranometer.

The data were stored on a data logger (Licor 1000) in the field. The data

logger, used for storage of the data, was changed weekly to avoid the loss of

data, and the recorded data were transferred to the computer regularly.

Tillering

The number of tillers or stalks was counted, periodically, for each

treatment from a specified sampling area in sugarcane. These data were

recorded at 98,129, and 187 days after planting. Data on the number of

primary and sucker stalks were also recorded at the time of the final harvest.

Crop Growth Rate

After the crops germinated, sample plots were marked off in each

treatment plot for collection of data on various growth parameters. Care was

taken to ensure that the number of developing plants in each sample plot was

comparable to the plant population in the remaining part of the treatment plot.

Data collected were leaf area index, plant height, free canopy height, canopy

width, percent canopy cover, ground cover with the dry falling leaves and

other crop residue, total fresh and dry weight at final harvest, grain yield in

sweet corn, total biomass, total cane yield, fresh and dry weight of sugarcane,

height and girth of the stalks and sugar content of the sugarcane.

49

Leaf Area Index. Leaf area index (LAI) is the total leaf area of a plant

subtended per unit of land area occupied by the plant (Chang 1968). LAI is

used as an indicator of plant growth and development for evaluating

assimilation and transpiration rates in plant physiological studies. It provides

indices of plant growth with time and is customarily used as an input for cr