GRAIN AND FORAGE LEGUME YIELDS, WITH OR WITHOUT INTERCROPPING

TABLE OF CONTENTS

ACKNOWLEDGEMENT ...........................................3

ABSTRACT ..................................................4

LIST OF TABLES ............................................11

LIST OF APPENDIX TABLES ...................................13

LIST OF FIGURES ...........................................14

LIST OF APPENDIX FIGURES ..................................16

CHAPTER I. INTRODUCTION ...................................17

CHAPTER II. REVIEW OF LITERATURE ..........................19

Terminology ..........................................19

Competition and Yield Advantages

in Intercropping ...................................20

Nitrogen Transfer from Legume to

Non-legume .........................................27

Green Leaf Manuring ..................................35

The Use of ¹⁵N-Labeled Fertilizers ................... 40

Evaluation of Intercropping

Experiments ........................................43

CHAPTER III. GRAIN LEGUMES WITH OR WITHOUT

INTERCROPPING WITH CORN (Zea mays L.) ................47

INTRODUCTION .........................................47

MATERIALS AND METHODS ................................49

Removal of Available N from Soil .....................49

Fertilization ........................................50

Planting of the Experiment ...........................50

Weed and Insect Control ..............................51

Harvesting ...........................................51

Plant Height_, Number of Pods, per

Plant and LAI ......................................54

Nitrogen Fixation ....................................54

Dry Matter Yield .....................................54

Nitrogen Content .....................................54

Nitrogen Recovery ....................................55

Evaluation ...........................................55

RESULTS AND DISCUSSION ................................56

Performance of Corn in Intercropping ..................56

Performance of Grain Legume in

Intercropping .......................................62

Total Performance in Intercropping ....................66

Corn Following Grain Legumes ..........................70

Environmental Effects .................................77

Nitrogen Yield and Transfer ...........................79

N Recovery from Urea .................................86

Soil Nitrogen .........................................90

Effects on Nitrogen Fixation ..........................90

SUMMARY AND CONCLUSIONS .................................95

CHAPTER IV. FORAGE LEGUMES WITH OR WITHOUT INTERCROPPING

WITH CORN (Zea mays L.) ............................99

INTRODUCTION .......................................99

MATERIALS AND METHODS .................................100

Planting ..............................................101

Weed and Insect Control ...............................102

Harvesting ............................................102

Plant Height and LAI ..................................103

Dry Matter Yield ......................................103

Nitrogen Contents .....................................103

Evaluation ............................................104

RESULTS AND DISCUSSION ................................104

Performance of Corn in Intercropping ..................104

Performance of Forage Legumes .........................110

Total Performance in Intercropping ....................116

N Yields and Transfer .................................119

Performance of Corn Following Forage

Legumes .............................................123

SUMMARY AND CONCLUSIONS ...............................125

CHAPTER V. EVALUATION OF LEUCAENA (Leucaena Leucocephala

(Lam.) de Wit) AS A GREEN LEAF MANURE FOR CORN

(Zea mays L.) ..............................................132

INTRODUCTION .......................................132

MATERIALS AND METHODS .................................133

Treatments ............................................133

Planting ..............................................134

Observations ..........................................135

Evaluation ............................................135

RESULTS AND DISCUSSION ................................136

Performance of Corn in Season 1 .......................136

Performance of Corn in Season 2 .......................138

Nitrogen Recovery .....................................145 Correlations ..........................................148

SUMMARY AND CONCLUSIONS ...............................148

CHAPTER VI. NITROGEN UPTAKE BY WHEAT CROPS FROM

¹⁵N-LABELED LEGUME PLANT MATERIALS .....................153

INTRODUCTION ..........................................153

MATERIALS AND METHODS .................................154

Tagging of Mungbeans ..................................155

Treatments ............................................155

Planting of Wheat .....................................156

Harvesting ............................................156

Evaluation ............................................158

RESULTS AND DISCUSSION ................................159

Yield of Wheat Crop 1 .................................159

Nitrogen Uptake by Wheat Crop 1 .......................161

Yields of Wheat Crop 2 ................................165

Nitrogen Uptake by Wheat Crop 2 .......................165

Nitrogen Recovery by Wheat ............................168

SUMMARY AND CONCLUSIONS ...............................176

APPENDIX TABLES .............................................178

APPENDIX FIGURES ............................................189

LITERATURE CITED ............................................205

CHAPTER II

REVIEW OF LITERATURE

Terminology

Legumes are frequently grown with non-legumes in some form of polycropping system (intercropping, relay cropping, mixed cropping or strip cropping). Intercropping is defined as the growing of two (or more) crops simultaneously on the same area of ground. Crops are usually grown simultaneously for a significant part of their lifecycle, hence intercropping is distinguished from "relay cropping" in which growing periods only briefly overlap. Crops are grown in separate rows in intercropping, and any arrangement where there is irregular broadcasting or mixing within the row is defined as "mixed cropping". In strip cropping, two or more crops are grown simultaneously in different strips wide enough to permit independent cultivation but narrow enough for the crops to interact agronomically.

Several other terms are used to describe various cropping systems; multiple cropping or polycropping is defined as a cropping system in two or more crops are grown on the same field in a year. Intercropping and sequential cropping are forms of multiple cropping. Sequential cropping is a system where two or more crops are grown in sequence on the same field per year.

Several other related terminologies commonly used in multiple cropping systems are sole cropping, monoculture or monocropping, rotation cropping, cropping pattern, cropping systems, and mixed farming. Sole cropping is the growing of one crop variety in pure stands, and is also called solid planting. Monoculture is the repetitive growing of the same crop on the same land. Rotation cropping is the repetitive cultivation of an ordered succession of crops on the same land. A cropping pattern is the yearly sequence and spatial arrangement of crops or of crops and fallow in a given area. A cropping system is the cropping patterns used on a farm and their interaction with farm resources, other farm enterprises, and available technology which determine their makeup. Mixed farming is the cropping systems which involve the raising of crops, animals, and/or trees, and such systems are also called farming systems.

Competition and Yield Advantages in Intercropping

Intercropping systems are more complex than monoculture systems. There is both inter - and intra - crop competition in intercropping systems in contrast to only intra-crop competition in monocultures. Allen et al. (l976), in a review of the literature, classified interaction between two species populations as follows: a) commensalistic, where the interaction between crop species has a positive net effect on one species and no effect on the other species, b) amensalistic, where the interaction between crop species has a negative net effect on one species and no effect on the other species, c) monopolistic, where the interaction between crop species has a positive net effect on one species a negative effect on the other species, and d) inhibitory, where the interaction between crop species has a net negative effect on all species.

Several other terms are also used to describe the interaction between two species growing together (Willey, 1979a). When the actual yield of each species is less than expected it can be termed as "mutual inhibition" and is rare in practice. In the second situation, where the yield of each species is greater than expected, it can be termed "mutual cooperation" and is not unusual. In the third situation, where one species yields less than expected and the other yields more, it can be termed as "compensation" and is the commonest situation.

In general, there are yield advantages in intercropping over monocropping. These yield advantages occur when: 1) the combined intercrop yield exceeds the yield of the higher-yielding sole crop, 2) the intercropping gives a full yield of a "main" crop plus some additional yield of a second crop, and 3) where the combined intercrop yield exceeds a combined sole crop yield (Willey, 1981).

Legumes are well known for their important role in various cropping systems (Francis et al., 1975; Dart and Krantz, 1977; Moomaw et al., 1977; Pinchinat, 1977). Intercropping of short-duration pulses with pastures and field crops are very common in many parts of the world (Mahapatra et al., 1975; Saxena and Yadav, 1975, Singh and Prasad, 1975; Singh and Singh, 1975). Various grass/legumes mixtures in forage production are also widely practiced (Kretschmer et al., 1973; Keya, 1974; Kitamura and Nishimura, 1976).

Yields of both legume and non-legume are of often reduced in intercropping as compared with yields when they are grown alone (Dalal, 1974; Syarifuddin et al., 1974). Yields of legumes are usually more depressed than that of non-legumes in intercropping (Agboola and Fayemi, 1971). Finlay (1974), using several legumes, reported that reduction in yields on the intercropped legumes ranged from 18 to 43%.

Other reports (Roquib et al., 1973; Ahmed, 1976; Fisher, 1977; Gunasena et al., 1978) have shown a reduction on yield of legume but no effect on non-legume. Singh (1977) added 5 legumes to a crop of sorghum and reported that the sorghum intercrop yield exceeded the sole crop with all legumes: increases ranged from 8.4% with soybean to 34% with cowpea for fodder. Remison (1978) reported a stimulatory effect in corn and cowpea mixtures and an increase in relative yield total in mixtures as compared to monocultures. The value of the total yield of both legume and non-legume intercrop is almost always higher than that from either of the monocrops (Gomez and Zandstra, 1976; Ahmed and Gunasena, 1979).

The yield depression in one crop or both in intercroppinq system may be due to the competition effects and shading of one crop by another (Willey, l979a). The yield potentiality in a legume/non-legume intercropping depends on their growth patterns, nutritional requirements, and compatibility of the crops involved (Willey, 1979a, 1979b).

Competition among plants occurs for water, nutrients and light (Donald, 1963; Rhodes, 1970). In intercropping, plants may have top competiton for light and root competition for nutrients including water or both. Kitamura et al., (1981) using Desmodium intortum and Setaria anceps studied top competition between the two species. When only top competition was allowed, desmodium was a better competitor for light than setaria. But when only root competition was allowed, the root growth of setaria was dominant over desmodium, and the growth of desmodium was depressed. When both (top and root) competition was allowed (the normal situation in legume-grass mixtures), desmodium was a poor competitor. When legumes and grasses are grown together, competition among plants moderate the effects of environmental factors such as light (Stern and Donald, 1962), water, and soil nutrients (Blaser and Brady, 1950).

In general, shading decreases the photosynthetic capacity of leaves (Woledge, 1978) and thereby decreases the dry matter yield (Eriksen and Whitney, 1982). Wong and Wilson (1980) studied the effects of shading on the growth and nitrogen content of green panicgrass and siratro in pure and mixed swards. They reported that shading increased the shoot yield of green panicgrass while shoot yield of siratro decreased with shading. Nitrogen accumulation in green panicgrass was markedly improved by shading. Shaded green panicgrass had a higher leaf area index, better distribution of leaf area with height, and lower extinction coefficients. Individual leaves of green panicgrass grown in shade had greater photosynthetic activity than those grown in full sunlight, while shaded siratro had a lower leaf area index and lower photosynthetic potential than in the full sunlight. They suggested that the better growth of green panicgrass under shade might be due to improved N status of the plants compared with those in full sun. N uptake into the whole plant of green panicgrass was increased by up to 34 and 52% under 60 and 40% sunlight, respectively. Singh et al.(1974) have also reported higher photosynthetic rates for leaves of Panicum capillare grown at 70 and 50% light compared with full sun.

Mungbeans are a convenient crop for intercropping as they nature in a short period of time and thrive under a wide range of conditions. Agboola and Fayemi (1972) reported that the yield of corn in

corn/mungbean intercropping (3,080 kg ha^-1) was significantly higher than the yield in monocrop (l,790 kg ha^-1). Several other researchers (Gunasena et al., 1979; Das and Mathur, 1980; Kalra and Gangwar, 1980; Miah and Carangal_, 1980; Rathore et al., 1980) reported that corn yield was higher in corn/mungbean intercropping than that in a monocrop of corn.

In experiments involving grain legumes intercropped with corn, no adverse effect of mungbeans was found on the yields of corn but the mungbeans yields were decreased (Agboola and Fayemi, 1971; Ahmed, 1976; Singh and Chand l980).

Ahmed (1976) used several legumes intercropped with corn and reported that mungbean/corn intercropping provided the highest economic return among the crops tested. Advantages of growing mungbeans as an intercrop over monocrop have been observed with many crops: Corn (Yingchul, 1976; Gunasena et al., 1978; Ahmed and Gunasena, l979), sorghum and pearlmillet (De et al., 1978; Singh et al., l978), sugarcane (Chandra, 1978) and sunflower (Campos and Macaso, l976).

Growth habit or type of mungbeans may also have influence on the yield potentiality when grown with cereals. In soybeans, determinate type plants attain most of their growth before flowering begins but indeterminate types continue to grow even after flowering begins (Egli and Leggett, 1973). Reproductive and vegetative development of indeterminate soybeans occurs simultaneously over a longer time than determinate soybeans (Scott and Aldrich, 1970). Similar growth patterns may be true for determinate and indeterminate types of mungbeans, and thus indeterminate type mungbeans may have a longer reproductive period than determinate ones. A longer reproductive period is usually associated with higher yield in mungbeans (Kua et al., l970).

Soybeans are another grain legume widely used in intercropping with non-legumes. Nair et al. (1979) using soybeans, cowpeas, pigeon peas and groundnuts as intercrops with corn in India_, reported that soybeans were the most suitable in intercropping among the legumes tested. In a comparison of pure and mixed cultures of corn, rice_, soybeans and pigeon peas grown in various combinations, the advantages of soybean/corn intercropping were most apparent (Chatterjee and Roquib_, 1975).

Jagannathan et al. (1979) reported that the cultivation of corn and soybeans in 1:2 and 1:1 ratios increased the yield of corn grain equivalents compared with corn in pure stands. The corn grain protein content was increased in the mixed stands in the 1:2 ratio. The protein and oil contents in soybean seeds were not affected. Other experiments showed an increase in corn yield when intercropped with soybeans over the monocrop (Narang et al., 1969; Kalra and Gangwar, 1980; Rathore et al., 1980; Singh et al., 1980; Srivastava et al., 1980).

Other experiments showed decrease in corn yield when intercropped with soybean over the monocrops (Wong and Kalpage, 1976; Dalal, 1977; Cordero, 1978; Gunasena et al., 1979; Singh and Chand, 1980). Cordero (1978) reported that corn yield was 17% less when intercropped with soybeans. However, the leaf area duration of corn in corn/soybean mixtures was twice as long as in the monoculture and the productivity of the intercrop was 20 to 40% greater than when the crops were grown alone.

Most studies involving corn/soybean intercrops indicated that corn yields were usually not affected but the soybean yields decreased (Roquib et al., 1973; Ahmed, 1976; Singh, 1977; Mohta and De, 1980; Chowdhury, 1981; Searle et al., 1981). Mohta and De (1980) evaluated several systems of intercropping corn and sorghum with soybeans. They reported that the corn yields were not affected by intercropping with soybeans but sorghum yields were reduced. Though the seed yield of soybeans when intercropped was less than that of a monocrop, the combined grain yield of the two crops grown as intercrop was more than the individual components. Land equivalent ratio (LER) increased to a maximum of 48 and 31% by intercropping corn and sorghum with soybeans compared with the cereal monocrops. Superiority of intercropping soybeans with cereals over monocrop has also been demonstrated by other workers (Finlay, 1974; Beat 1977; Ibrahim et al., 1977).

Cordero and Mecollum (1979) applied various levels of N in corn/soybean intercrops and reported that as the rate of N application was increased, the corn yields increased and the soybean yields decreased. With the increased level of N, corn had better growth and was dominant over soybeans.

Leucaena leucocephala is a perennial tree legume that has recently attracted much attention. Efforts have been made to study corn/leucaena intercropping (Mendoza et al., 1975; Guevarra, 1976; IITA, 1979; Rosa et al., 1980; Kang et al., 1981b; Mendoza et al., 1981).

Guevarra (1976) observed no yield reduction in the yield of any crop in the corn/leucaena intercropping. He reported that crude protein yield in the corn/leucaena intercrop was 1.44 t ha^-1, which was twice the protein yield (0.75 t ha^-l) of corn alone with a nitrogen application of 75 kg N ha^-1, and three times the protein yield (0.47 t ha^-l) of corn with no nitrogen application.

At the International Institute of Tropical Agricultuce (IITA, 1979), intercropping of leucaena with corn, and with corn and cassava was studied. The corn yields in corn/cassava (3.1 t ha^-1) and corn/leucaena (2.8 t ha^-1) were higher than the corn alone (2.5 t ha^-1). Corn yield in corn/leucaena/cassava (l.8 t ha^-1) was lower than the corn alone but the cassava yield in corn/leucaena/cassava intercropping (29.2 t ha^-1) was higher than the corn/cassava intercropping (20.2 t ha^-1). This indicated that the joint effect of both crops adversely affected corn. The marked difference in cassava yields between corn/cassava and corn/leucaena/cassava indicated a beneficial effect of leucaena. This experiment suggested that intercropping of leucaena with corn and corn/cassava is a feasible recommendation for the establishment of leucaena in cropping systems.

Rosa et al. (1980) working on Leucaena/corn intercropping reported that leucaena decreased the time of maturity of the corn crop, and increased the ear length, ear diameter and grain yield of corn. Grain yields of corn were increased from 48.5 g/ plant in pure stand to 69.9-74.4 g/ plant in intercropping. Erosion on hills during heavy rains was greater in pure corn stands than intercropped corn.

Desmodium intortum is another perennial legume of interest in the tropics. Increases in forage yield and crude protein yield/ha by inclusion of desmodium with grasses has been observed by several workers (Younge et al., 1974; Whitney et al., 1967; Whitney and Green, 1969; Whitney, 1970). So far, only few studies have been made where desmodium was grown with cereal crops.

Nitrogen Transfer from Legume to Non-legume

The practice of intercropping a cereal and legume is based on the hypothesis that the cereal can utilize nitrogen fixed by the legume. The legume way increase the supply of available nitrogen in the root medium, but it may also compete with the non-legume for this nitrogen (Simpson, 1965). Most of the experiments have shown that non-legume benefits more from the increase in nitrogen supply than it suffers from competition by the legume, and there is a net transfer of nitrogen to the non-legume (Walker et al., 1954; Bryan, 1962).

In general, legumes are weaker competitors far mineral N than grasses (Henzell and Vallis, 1977). When legumes are substituted for non-legumes on a soil where the N supply is limiting, the remaining non-legumes are able to take up more mineral N per plant than they would in a pure stand of non-legumes, which is termed as the "N-sparing effect" of substituting nodulated legume for non-legume plants (Vallis et al., 1967).

In general, it is found that non-legume crops are unlikely to benefit from associated legumes sown at the same time unless the non-legume plants continue to take up N after the legume plants have begun to senesce and die. Thus, it seems that there may be two opposing considerations in the choice of the relative time of sowing legumes and non-legume crops in mixture. If the legume is sown early it may compete with the non-legume for soil mineral N but there could be an opportunity later for rapid and effective transfer of N to the non-legume companion crop. On the other hand, if the legume is sown late, the non-legume will already have taken up soil mineral N but there will be little or no opportunity for N transfer immediately and some legume N may even be lost before another crop can use it (Henzell and Vallis, 1977).

The non-legume may receive N fixed by a legume while grown together (Henzell and Vallis, 1977; Whitney, 1977), and or while grown after tile legume in rotation (Talleyrand et al., 1977; Lal et al., 1978; Singh and Awasthi, 1978; Ahlawat et al., 1981). Two major pathways by which N may be transferred from legume to non legume: 1. Above ground transfer including a) urine and dung of grazing stock, b) leaching of nitrogenous compounds from leaves by rain, c) decay of fallen leaves or other litter, and 2. Underground transfer including a) direct excretion of nitrogenous compounds from legume root systems and use by non-legume root system, and b) sloughing off and decay of nodule and root tissue (Virtanen et al., 1937; Walker et al., 1954; Whitney and Kanehiro, 1967; Scott, 1973).

Virtanen et al. (1937) conducted extensive experiments which showed that leguminous plants were able to excrete N into the substrate in which they were growing and that the N may be utilized by associated non-leguminous plants. Similar results showing N excretion were reported by other workers (Wilson and Wyss, 1937; Wilson and Burton, 1938; Whitney and Kanehiro, 1967).

In grain legumes, some evidence of N excretion was shown by Vest (1971) in experiments where non-nodulating soybeans, grown in half and halt mixture with two nodulating cultivars, had higher yields, higher percent protein and larger seed size than the non-nodulating line grown in pure culture.

In another experiment, Burton et al. (l983), growing nodulating and non-nodulating soybean isolines in pure and in mixed cultures, reported that the average performance of the non-nodulated component of the mixture was 38% greater than the average yield of the non-nodulated line in pure cultures, indicating that non-nodulated isolines benefited from nodulated isolines in mixed culture. Singh et al. (1974) found that yield and percent N of non-nodulating soybeans increased as the frequency of nodulating border rows increased, indicating the N release from nodulated plants to non-nodulated plants.

Release of N from the legume and its transfer to an associated non-legume is significant only when vigorous legume growth occurs. This N transfer is more common in perennial than in annual legumes (Whitney et al., 1976). Seasonal conditions such as long days, low temperatures and shading seem to favor N excretion (Wilson and Wyss, 1937; Wilson, 1940; Wyss and Wilson, 1941; Butler et al., 1959). Carbon/nitrogen ratios have also been reported as a governing factor in N fixation and N excretion by legumes (Virtanen, 1947). Brief wilting has also been found to cause N excretion (Katznelson et al., 1955).

Most of the experiments indicated that the transfer of N from living root system of legumes is only a small percentage of the total N fixed (Henzell, 1962; Simpson, 1965; Vallis et al., 1967; Whitney and Kanehiro, 1967; Henzell et al., 1968). The amounts of N turnover by the decomposition of sloughed nodules, root tissues and foliar residues are probably more important than the direct transfer of N between the legumes and non-legumes (Misra and Misra, 1975; Subbarao, 1975; Tiwari and Bisen, 1975; Simpson, 1976; Henzell and Vallis, 1977; Vallis, 1978; Whitney, 1982).

The availability of N from legume residues depends on the rate of the mineralization process. The proportion of N released during decomposition of the residues in governed by the chemical of these residues, especially the N content, the manner in which the residues are returned to the soil, and the environmental conditions. The chemical composition of legume residues depends to a large extent on the proportion of different plant parts and their maturity (Henzell and Vallis, 1977).

Amounts of N returned to the soil in the form of legume residues vary widely according to the legume yield and whether or not it is utilized for grain, forage, grazing or green manure. N content in grain legume residues may be lower than that in pasture legumes (Henzell and Vallis, 1977). Henzell and Vallis (1977) reported a N-content ranges of 3-5% in tops and 2-4% in roots in some pastures legumes. Hanway and Weber (1971) recorded 2% N in the fallen leaves from a mature soybean crop and 0.9% N in the stems and roots. Plant residues containing more than 1.8% N usually mineralize N immediately, and those with less than 1.2% N usually immobilize it temporarily (Alexander, 1961).

Part of the N in legume residues quickly becomes available for reuptake and the remaining N after the initial flush of mineralization becomes available only very slowly for later crops (Henzell and Vallis, 1977; Vallis, 1978). Bartholomew (1965) estimated that about 60% of the N in legume residues is likely to be mineralized in time for the following crop. The remainder is lost or is incorporated into the soil organic matter which may become slowly available for later crops. Henzell and Vallis (1977) reported that as much as 30% of the tropical legume residues were mineralized and taken up by the companion grass after 24 weeks.

The rate of mineralization of plant materials also depends on the method of its application. Fresh plant material mineralizes at a faster rate than dried material (Schreven, 1968) and buried residues decay at a faster rate than do surface residues (Moore, 1974).

The mineralization process is affected by several other factors. Higher soil temperature enhances mineralization, higher soil moisture reduces mineralization (Cassman and Munns, 1980). Cultivation may also enhance the rate of mineralization (Arnott and Clement, 1966; Powlson, 1980). Addition of phosphorus in P deficient soils has been found to enhance nitrification (Purchase, 1974). Grass root extracts have been reported to suppress nitrifying bacteria (Theron, 1951), however, in lower concentration grass and legume root extracts have also been reported to increase the rates of N mineralization and nitrification (Odu and Akerle, 1973).

Mineral N from decomposing plant material may also be lost from the soil in a solution or in a gas form by leaching, volatilization and denitrification (Tanaka and Mavasero, 1964; Watson and Lapins, 1964; Bartholomew, 1965; Cornforth and Davis, 1968; Kilmer, 1974).

In an experiment, when crop residues were plowed under the soil, the N in the returned herbage was subject to loss unless taken up by plants (Watson and Lapins, 1964). It was reported that when dried clover and grass herbage (3.86% N) was applied to an annual grass pasture, that for each 100 lbs. of herbage N applied, 11 lbs. were taken up by grass plants, 46 lbs. were lost by volatilization or leaching, and the remaining 43 lbs. were recovered in the soil. Other experiments have also shown the loss of N from plant residues of soybeans (Suttle et al., 1979), corn (Terman and Allen, 1974) and spring wheat (Boatwrite and Haas, 1961). Losses of N from urine (54% N loss) after 8 weeks of urine application in summer(Watson and Lapins, 1969) and losses of up to 80% of N from cattle dung lying on the soil surface in a warm climate have been reported (Gillard, 1967). Loss of nitrates by leaching may be reduced by growing deep-rooted crops like corn, and the role of a deep-rooted crop (like corn) in reducing losses of nitrate is further enhanced in intercropping systems (Singh et al., 1978).

Significant losses of N are common from the N-fertilizer applied in to the soil. A review of the literature by Allison (1966) indicated that average crop recovery is about 50% of the N applied. Other experiments (Soper et al., 1970; Toews and Soper, 1978) with barley have shown similar recovery (50%) from N fertilizers broadcasted. N recovery, however, was increased to 60% by band application of N fertilizers.

The amount of N contribution from legume to an associated non-legume or to a subsequent crop depends on the N fixing ability and N requirement of the legume. The amount of N fixed is determined by many factors including plant species, plant density, climatic conditions effectiveness of bacterial strain, soil ph and nutrient status, and the amount of available N in soil (Allison, 1965).

The quantity of N fixed by legumes is variable and a wide range in amount of N fixed by legumes has been reported from a few kilograms to 700 kg N ha^-1 yr^-1 (Nutman, 1971; Date, 1973; Jones, 1974; Graham and Hubbell, 1975). Annual legumes seem to fix appreciably less N ha^-1 yr^-1 than perennial legumes due to a shorter growing season for annuals (Nutman, 1971) . In perennials at least one third of the fixed N is concentrated in the root mass, while in annual legumes, when ripe for harvesting, most of the N assimilated from the atmosphere is in the tops of the plants (Sundara Rao, 1975).

A wide range of amounts of N fixed by mungbeans has been reported by several workers, 6 to 32 kg N ha^-1 yr^-1 (Gomez and Zandstra, 1976) and 325 kg N ha^-l yr^-1 (Agboola and Fayemi, l972). Many workers (Agboola and Fayemi, 1972; Misra and Misra, 1975; Saraf and De, 1975; Singh and Singh, 1975) demonstrated that mungbeans were more beneficial in rotation with cereal crops than as a companion crop. Residual N from mungbeans were reported to be 22 kg N ha^-1 (Agboola and Fayemi, 1972) and 25 kg ha^-1 (IARI, 1976) in one season. Agboola and Fayemi (1972) reported an excretion of 3% N fixed by mungbeans at flowering time.

Various estimates of amounts of N fixed by soybeans have been reported. In several experiments, soybeans fixed 84 kg N ha^-1 (Weber, 1966a, 1966b), 93 to 160 kg N ha^-1 (Vest, 1971), 148 to 163 kg N ha^-1 (Weber et al., 1971), and 17 to 369 kg N ha^-1 (Gomez and Zandstra, 1976). Schroder and Hinson (1974) studied the nodulating and nonnodulating soybeans grown in rotation with winter rye and in mixture with rye, and reported that roots of modulating soybeans left a considerable amount of N in the soil. Saxena and Tilak (1975) reported that wheat following a soybean crop received 30 kg N ha^-1 as a residual N from the soybean crop.

Perez-Escolar et al.(1978), using soybean, mungbean and wingbean legumes followed by corn crop, reported that in all cases corn following the legume had higher yields than corn following corn. About 80% of the maximum corn yield was attained when corn followed the legumes and with no fertilizer N applied. Shrader et al. (1966) showed that approximately 90 kg N ha^-1 was available to corn following soybeans.

Leucaena (Leucaena leucocephala) has been reported to fix a very high amount of atmospheric nitrogen. The amount of N fixed was reported as 500 kg N ha^-1 yr^-1(Guevarra, 1976) and a range of 310 to 800 kg N ha^-1yr^-1 (Brewbaker et al., 1972; Gomez and Zandstra, 1976). Guevarra (1976), working with corn/leucaena intercropping, incorporated leucaena in the soil and reported that leucaena contributed significantly to reducing the nutritional requirement of the intercropped corn. Yield of intercropped corn with leucaena incorporation in the soil was comparable to yield of corn where 75 kg N was applied as urea. Harvesting and incorporation of leucaena in intercropped corn at early stage of corn was more beneficial than at later stages.

Sears (1953) reviewed a number of New Zealand experiments and concluded that 50 lbs. out of 230 lbs. N A^-1 fixed annually by white clover was transferred to associated grass at one location, and 140 lbs. out of 500 lbs. N A^-1yr^-1 was transferred at another location. Herriott and Wells (1960) found that white clover transferred about 50% of its fixed N to rye grass and about 33% to orchard grass. In other cases, however, only a small amount or no N transfer from legume to associated grasses have been reported (Walker et al., 1956).

Whitney et al. (1967) reported that Desmodium intortum fixed 340 lbs. N ha^-1yr^-1 and about 5% was transferred to the associated grasses. Transfer of fixed N from desmodium to the associated grass was reported to be as little as 1.66% in sand culture (Henzell, 1962) to as much as 20% to pangolagrass (Whitney and Green, 1969). In small plots (nongrazed) transfer of nitrogen is small but in grazed plots (through animal urine, trampling, etc.) transfer would be expected to be much greater (Henzell and Vallis, 1977). Henzell et al. (1966) reported the accumulation of 90 to 100 lbs. of N A^-1 yr^-1 in soil by desmodium.

One of the problems usually observed in cereal/legume intercropping is shading of legumes by cereals. Shading decreases the availability of light to the legume and thus less photosynthates are available for the rhizobium to continue N fixation (Bethlenfalvay and Phillips, 1977; Eriksen and Whitney, 1982). Reduced nodulation and reduced nitrogen fixation in legume in cereal/legume intercropping has also been reported in soybean (Reddy and Chatterjee, 1973; Wahua and Miller, 1978a, 1978b), dry beans (Graham and Rosas, 1978) and desmodium (Whiteman, 1970).

Kitamura et al. (1981) studied the competition between Desmodium intortum and Setaria anceps and reported that nodule numbers were depressed by both top and root competition but the legume plants were able to compensate by increases in nodule size and increases in acetylene reduction activity per unit of nodule weight (specific nitrogenase activity).

Increase in nodule activity in soybean has been observed with up to 18% shading (Trang and Giddens, 1980) and with 20% shading (Wahua and Miller, 1978a, 1978b). Shading reduced the number of small-sized

nodules, and increased the efficiency of bigger-sized nodules in up to 20% shading then nodule activity rapidly declined with increasing shade.

Studies of ICRISAT (1977) included the efficiency of nitrogen fixation in pigeon peas when interplanted with sorghum. Pigeon peas had better nodulation when the roots intermingled with those of intercropped sorghum. Thompson (1977) reported an apparent increase in nodule number and weight of soybeans growing with corn. He explained that the cereals depleted soil nitrogen, thus stimulating the nitrogen fixation by legumes.

Green Leaf Manuring

Green manuring has been in practice from ancient times and at the present is becoming of increasing importance due to the increasing costs and unavailability of nitrogenous fertilizers in many parts of the world. Green manure crops are those crops grown solely to benefit concurrent of subsequent crops by increasing soil fertility and improving soil physical properties. Green-leaf manure crops are grown on adjacent sites and periodic loppings or prunings are used to fertilize another crop. Legumes, having N fixing capacity and high N content in foliage, can play a vital role as green manure crops.

Much of the experimental work on green manures has been done with rice. In a pot study, Mahalingam et al. (1975) found the yield response to green-leaf manure N equivalent to calcium ammonium nitrate and greater than ammonium sulfate when N was applied equally for the sources at 67 kg ha^-1. Ali and Morachan (1974) reported that IRRI rice varieties produced 5.3 and 5.9 t ha^-1 grain, respectively, for Crotalaria juncea green-leaf manure (25 t ha^-1 and an equal amount of N (187.5 kg ha^-1 as ammonium sulfate, compared to 4.2 t ha^-1 grain when the N was supplied as farm yard manure. Patnalik and Rao (1979), reviewing N sources of rice, concluded that on an equal-N basis, at moderate levels of 20 to 40 kg N ha^-1, green manure was as efficient as inorganic N.

In one experiment in Peru, Wade and Sanchez (1983) used kudzu (Pueraria phaseoloidy) and guinea grass (Panicum maximum) as mulches or as incorporated green manures under three fertilizers treatments. Kudzu incorporated at the rate of 8 tons fresh material/ha/crop produced yields which were 90% of the crops receiving complete inorganic fertilization (120 kg N ha^-1). The beneficial effects of incorporating kudzu as green manure were associated with the amounts of N, P, K, Ca and Mg released from the decomposing material, and decreased Al saturation. Mulching produced about 75% of the crop yield achieved with completely fertilized plots.

In corn experiments, Ruiz and Laird (1961) found that C. juncea green manure provided 84 to 97 kg ha^-1 N in the green matter which resulted in a grain yield greater than the fallowed control by over one ton, and equivalent to inorganic N at 80 kg ha^-1. Stickler et al. (1959) in Iowa reported a corn response (95% of maximum yield) to 122 kg ha^-1 N in green-manured legume tops and roots as compared to from 56 to 112 kg ha^-1 inorganic N.

Residual effects of green manures on corn are generally nonsignificant, but occasional responses are reported. Eusebio and Umali (1952) working with pulses, reported that cowpea green manure increased yields of the second successive corn crop also. In Indonesia, Van de Goor (1954) reported that C. juncea grown after corn as green manure for rice increased corn yield in the following cycle. Rattray and Ellis (1952) found that the second corn crop grown after a green manure crop produced only one-half the yields of the first crop.

Evans (1981) using C. juncea as a green-leaf manure in a corn crop reported that green-leaf manure produced corn yields equivalent to urea at low (under 100 kg ha^-1) N rates and that the residual effects of

green manure to next crop of corn was less than 50 kg ha^-1 N rate of urea application.

Leucaena with a capacity for fixing high amounts of atmospheric nitrogen (310 to 800 kg N ha^-1 yr^-1) and its multiple uses (Brewbaker et al., 1972; Gomez and Zandstra, 1976) has attracted attention of researchers for its use as green-leaf manure because ofits high N content in foliage. Only limited work has been done on the leucaena as a green-leaf manure.

There are two basic types of systems involving leucaena use as a fertilizer and soil ammendment. In the first, hedge rows of leucaena are intercropped with food crops, also called as "alley cropping." In this system leucaena foliage are periodically pruned and mulched or incorporated into the soil for use by the companion food crop growing in the same field. The second involves sole cropping of leucaena for cutting and transporting to another field. This "cut and carry" system constitutes an export of nutrients from one field to another.

Guevarra (1976) intercropped corn with leucaena to compare the yield and N uptake response of corn to N supplied from leucaena greenleaf manure and from urea. He estimated the N contribution of leucaena green manure (forage) to the corn on the basis of: 1) the concentration of N in the corn plant tissue samples, 2) the weight of corn seedlings, and 3) grain yields. He reported that the yield of intercropped corn with leucaena incorporation was comparable to yield of corn where urea was applied at the rate of 75 kg N ha^-1.The efficiency of leucaena in supplying N to corn was about 38% of that of urea.

In studies at the International Institute of Tropical Agriculture (IITA) in Nigeria, Kang et al. (1981a) used leucaena prunings as green-leaf manures in pot studies and in field trials in which crops were

grown between widely spaced hedges of leucaena in a system they called "alley cropping." They found that incorporation of prunings produced higher corn N-uptake, ear leaf N concentration, and grain yields than when applied as mulch. In the alley cropping trial, grain yields were significantly increased over the control (no N applied). Application of l00 kg ha^-1 of fertilizer N, 10 t ha^-1 of leucaena prunings, or 50 kg ha^-1 fertilizer N plus 5 t ha^-1 of pruning treatments produced 4.5, 3.7, and 3.5 t grain ha^-1, respectively, in contrast to 2.6 t ha^-1 for the no N control. Kang et al. (1981b) in field studies also reported the suitability of leucaena as a green-leaf manure in corn/leucaena alley cropping system as a low N-input system.

In four year of study of corn with leucaena in alley cropping, 5 to 6 annual prunings of leucaena yielded 5 to 8 tons of dry prunings

ha^-1 yr^-1, which contained 180 to 250 kg N ha^-1 yr^-1 (Kang et al., 1981b).

This annual green-leaf manure addition sustained corn grain yields at 3.8 tons ha^-1 yr^-1 with no N fertilizer application while yields declined with no green-leaf manure.

In the above trial (Kang et al., 1981b), 5 corn rows per “alley” were harvested separately during two seasons. In the first season, corn yields were significantly lower in the rows bordering leucaena badges. In the second season, in which the timing of leucaena prunings was done so as to minimize shading of the corn, there was no significant difference between yields from various rows. This indicates that shading is a main factor of competition between intercropped corn and leucaena and that timing of leucaena pruning must be done to minimize this shading.

In another experiments (Mendoza et al., 198l), corn was grown alone or intercropped between hedges of leucaena 3 m apart and herbage from leucaena was applied as green manure at 9.44 t ha^-1. Application of green manure increased corn fodder yields from 3.59 t in corn alone to 8.24 t dry matter ha^-1. In a further trial corn intercropped with leucaena hedges 3 or 4.5 m apart and with 9.85 and 7.84 t green manure ha^-1 yielded 11.02 and 9.94 t fodder ha^-1 and 8.99 and 7.58 t marketable ears ha-¹, respectively. Pure corn stands given 45 to 90 kg N gave 4.59 and 14.44 t fodder ha^-1 and 9.07 and 8.11 t marketable ears ha^-1, respectively.

At IITA in 1981, Read (1982) studied several important leucaena green-leaf manure management alternatives, including; application of fresh vs dried leaves, mulching vs incorporation of leaves, and split application vs application of complete rates at planting. Results of the corn in this trial showed that dry weight gain in corn at 40 days was significantly higher with fresh-leaf than with dry-deaf application. Incorporation was significantly better than mulching with fresh but not, with dry leucaena leaves. He also found that there was, no difference in applying the leucaena at planting and splitting the application with 1/3 at planting and 2/3 four weeks later. Read (1982) determined the field decomposition rates of leucaena by measuring loss of organic matter in 2 mm mesh nylon bags. It was found that the decomposition rate of fresh and dried leucaena foliage was significantly faster when buried rather than mulching.

In Hawaii, Evensen (1983) evaluated both mulching and incorporation methods of leucaena application in corn, where leucaena green leaves were applied at the rates of 57, 114, and 171 kg N ha^-1. This study showed that incorporation of leucaena leaves was superior than the mulching method. N recovery by corn in this study were found to be 57.9, 31.7 and 18.4% for urea, leucaena leaves incorporated, and leucaena leaves mulched, respectively.

The Use of ¹⁵N-Labeled Fertilizers

Tracer techniques based an the use of the stable isotope ¹⁵N are common in nitrogen research. The ¹⁵N isotope was discovered by Naude (1930), and practical methods for its use was reported by Urey et al. (1937). The first application of ^l5N in agronomic research was by Norman and Werkman (1943), who used it to study the uptake of nitrogen by soybeans.

The use of tracers is based on the fact that ¹⁴N and ¹⁵N occur naturally in a almost constant ratio. The ratio of ¹⁴N to¹⁵N in nature is found to be 272:1 (Hauck and Bremner, 1976). Addition of ^l5N material in a system causes a change in ¹⁴N to ^l5N ratio in that system, which gives an idea of the extent to which the tracer has interacted with and become a part of the system. At present, the ratio of (¹⁴N¹⁴N) to (¹⁴N¹⁵N)is measured by mass a spectrometer and recently also by an emmision spectrometer.

Reviewing the literature, Hauck and Bremner (1976) indicated that nitrogen tracers have been used to study nitrogen mineralization - immobilization reactions in soil, gains of N by, and losses of N from soil and water, plant recovery of applied N, N movement through soils to water, N balance in ecological systems, and virtually all known aspects of N cycle processes.

Several recent works indicated extensive use of ¹⁵N-tracer technique in many areas of research: N fertilizer efficiency (Tomar and Soper, 1981; Wetselaar, 1983), N leaching (Malhi and Nyborg, 1983; Priebe et al., 1983; Sompangse et al., 1983), denitrification (Malhi and Nyborg, 1983; Novak and Blackmer, 1983), decomposition of plant residues (Herridge, 1982), N transfer from legume to grass (Ismaili, 1983) and N excretion by legumes (Burton et al., 1983).

The use of ¹⁵N-tracers has made it possible to study the proportion of N derived from fertilizers, soil and atmospheric fixation. In nonleguminous plants, where the N sources are only soil N and fertilizer N, the proportion of N derived from the applied fertilizer can easily be measured with the use of ¹⁵N-labeled fertilizer. In case of leguminous plants, where three sources of N are available for plant’s use, however, this analysis becomes complex.

The first use of ¹⁵Nin N₂ fixation research was by Burris and Miller (1941) in studies of N₂ fixation by Azotobacter vinelandii. Since then there has been extensive use of ¹⁵N-tracers for measuring N₂ fixation. Even with the use of ¹⁵N-tracer, the problem remains there as the total N of plants consist of labeled N from fertilizers, and unlabeled N from soil and fixed N and it is difficult to separate soil N from fixed N, since both are unlabeled. This problem was resolved by Fried and Broeshart (1975) who suggested the use of non-fixing crop as the reference crop adjacent to fixing crop. In this method ¹⁵N-labeled fertilizer is applied to both non-N-fixing and N-fixing crops grown under identical soil conditions. The available amounts of soil plus fixed N are determined using the legume crop, and the available amount of soil N is determined using the reference crop.

Legg and Sloger (1975) developed a ¹⁵N-tracer technique better suited for evaluation of N₂ fixation under field conditions in which they incorporated ¹⁵Ninto the soil organic N, and then this ¹⁵N-labeled soil organic matter was used as the tracer material. The use of ¹⁵Nlabeled soil organic matter (Legg and Sloger, 1975) may have two advantages over the ¹⁵Nstudies in which ¹⁵N-labeled fertilizer is used as the tracer material (Fried and Broeshart, 1975). The first advantage is that incorporation of ¹⁵Ninto the soil organic fraction using carbon substrate also ties up the available soil N, thus, the N input from the soil results from mineralization of labeled soil organic N, in contrast to ¹⁵Nfertilizer methods, where the N inputs from soil consist of soil and fertilizer N. The second advantage is that the incorporation process reduces the amount of combined N available to the plants and thus promotes N₂ fixation. The ¹⁵Nfertilizer method, in contrast, increases the amount of available N which tends to depress N₂ fixation levels (Harper, 1976). The use of ¹⁵N-tracers for the measurement of N₂ fixation has recently become popular (Fried and Broeshart, 1981; Broadbent et al., 1982; Rennie, 1982; Rennie et al., 1982; Talbott et al., 1982; Wagner and Zapata, 1982; Jones and Foster, 1983).

¹⁵N-tracer techniques have also been used in studies dealing with evaluation of uptake of N from plant residues (Yaacob and Blair, 1980; Herridge, 1982). Herridge (1982) grew a wheat crop on soil amended with ¹⁵N -labeled plant residues of Medicago spp. and deported that only 11-17% of the ¹⁵N-labeled medicago residues added to the soil were utilized by a succeeding wheat crop, while 72 to 78% remained in the soil organic pool.

In another experiment, Yaacob and Blair (1980) used soil from plots that had grown 1, 3, or 6 crops of soybeans or siratro. ¹⁵N - labeled residues from soybeans and siratro were added to half the plots in the experiment and the other half was left unamended, and then rhodegrass was grown. They reported that N uptake by the grass increased with number of previous cycles and was higher in siratro than soybean soils. The total recovery of 15N from soybean residues were 14.7, 14.6 and 16.8% from soils cropped to 1, 3 and 6 previous soybean crops, respectively. In contrast, the total ¹⁵N recovery from siratro residues were 13.7, 42.4 and 55.5% from soils cropped to 1, 3 and 6 siratro crops, respectively.

In an experiment, Pomares-Garcia and Pratt (1978) used various rates of manure and sludge combined with ¹⁵N-labeled ammonium sulfate and grew barley and sudangrass as test crops. He reported that 37.2 to 70.2% of the N from ammononium sulfate was recovered by the first cutting of barley forage and a range of 0.7 to 8.9% recovered by sudangrass, which was the last crop of the cropping sequence.

In a recent study, Ladd et al., (1983) grew two crops of wheat on a soil mixed with ground ¹⁵N-labeled legume material (Medicago littoralis) and reported that the first wheat crop took 20.2 to 27.8% of the legume N applied at the rate of 48.4 kg ha^-1. The uptake of N from legume residues to a second wheat crop declined to 4.8% of legume N applied. For both first and second wheat crops, uptake of N from legume residues was approximately proportional to legume N input over the range of 24.4 to 96.8 kg ha^-1. The proportions of wheat N derived from added legume N were 32 to 65% for grain and 5 to 6% for roots. These studies indicate that ¹⁵N-labeled organic residues can successfully be used in the evaluation of N uptake from plant residues.

Evaluation of Intercropping Experiments

The evaluation of cropping system in intercropping situation become more complex as compared to monocropping situations, where only one crop is involved. When two crops are grown in intercropping, one crop interferes with another, and therefore, they cannot be considered growing independently, hence yield performances cannot he evaluated separately in intercropping experiments.

To fully analyze the intercropping situation, one needs to combine the performances of all crops in some way, however, and this is where difficulties arise. Strict addition of yields is usually meaningless where they are of very different types, but this is usually the case in most intercropping experiments. It was suggested that the yield performances in intercropping experiments be converted in terms of some common parameters (Willey, 1979b).

Usually two approaches are used to evaluate intercropping experiments. One is an economic approach, where crop yields are converted in terms of money, and then cost/benefit, profitability or monetary advantages are calculated. The other is an energetic approach, where crop yields are converted in terms of calories, proteins, nitrogen, digestible nutrients, dry matter etc. to evaluate the total productivity in the intercropping situation. These conversions to common parameters provide opportunity to better evaluate the intercropping situation even with crops of diverse nature. Objections were raised however by Pearce and Gilliver (1978) in using these two approaches for evaluation, who said that the monetary value is subject to fluctuating market conditions. Caloric value may appeal to the dietician but it does not enter into the consciousness of the peasant farmer, who is the one to be persuaded.

The main objective of most intercropping experiments has been to investigate the output of the intercrop compared with the monocrop situation and to whether or not intercropping provides any advantage over monocropping. The most commonly used method of evaluating intercropping experiments is the use of the Land Equivalent Ratio (LER). LER is defined as the relative land area under monocrops that is required to produce the yields achieved in intercropping under the same management (Willey, 1979a). LER is calculated as the sum of the ratios of dry weight yields of each crop in a mixture over its yields in pure culture. LER provides an accurate assessment of competitive relationships between components as well as overall productivity of the intercrop system. When, LER = 1 , the overall yield per unit of area of intercrop is never greater than that of the most productive monocrops, and there is no yield advantage in intercropping. In another situation, if LER > 1, it implies that the intercrop outyields the monocrop and there are yield advantages in intercrop over monocrop.

Another method used in competition studies is the Relative Yield Total (RYT) by de Wit and Van den Bergh (1965). RYT is calculated in the same way as LER, but it is on a yield basis rather than a land-area basis as in LER. A mixture of crops could be economically advantageous if the RYT is greater than 100%.

In addition to LER and RYT, methods such as calculations of Relative Crowding Coefficient, Aggressivity and Competition Index are used to describe competitive relationships and to evaluate yield advantages in intercropping experiments (Willey, 1979a). Relative Crowding Coefficient was proposed by de Wit (1960) and examined in detail by Hall (1974a, 1974b). In this method, each species has its own coefficients (K) which gives a measure of whether the species has produced more, or less yield than expected. Relative Crowding Coefficient is calculated as the ratio of yield of a species in mixture over the yield difference between yield in pure stand and yield in mixture. If the product of Relative Crowding Coefficient of all species, K > l, then there is yield advantage, if K = 1 there is no differences, and K < l then there is yield disadvantage.

Aggressivity, proposed by McGilchrist (1965), gives a simple measure of how much the relative yield increase in species "a" is greater than that for species "b". In a mixture of two species, Aggressivity can be calculated as the difference between the ratio of mixture yield of "a" over expected yield of "a" to mixture "b" over expected yield of "b". An Aggressivity value of zero indicates that the component species are equally competitive. For dominant species this value is positive and for dominate species the value is negative.

A Competition Index was suggested by Donald (1963). The basic process is the calculation of equivalence factors for each species. For species "a" the equivalence factor is the number of plants of species

"a" which is equally competitive to one plant of species "b". If a given species has an equivalence factor of less than one it means it is more competitive than the other species. The competition index is the product of the two equivalence factors. If the competition index is less than one there has been an advantage of mixing species.

In terms of economic approach of evaluation, monetary advantage is quite often calculated, where monetary advantage = value combined intercrop yield X (LER - 1)/LER. Income Equivalent Ratios are sometimes used (conversion of LER into income terms). It is the land area needed under sole cropping to produce the same gross income as in one hectare of intercropping at the same management level. However, Land Equivalent Ratio and Relative Yield Total are most commonly used to evaluate intercropping experiments.

CHAPTER IV

FORAGE LEGUMES WITH OR WITHOUT INTERCROPPING WITH CORN (Zea mays L.).

INTRODUCTION

Forage legumes are grown with grasses to increase yields as well as to improve the nutritional value of the forages. In addition to increased yields and nutritional value, the practice of legume/grass mixtures is based on the assumption that grasses utilize nitrogen fixed by legumes.

Forage legumes are included in cropping with foodcrops. One of the major food crops grown in these cropping is corn. Among the legume forage legumes, leucaena, because of its multiple uses, is popularly grown with corn. Efforts have been made to grow leucaena with corn (Mendoza et al., 1975; Guevarra, 1976; IITA, 1979; Rosa et al., 1980; Kang et al., 1981b; Mendoza et al., 1981). In a corn/leucaena intercropping experiment, no reduction in yield of either crop was observed by Guevarra (1976). At IITA (1979), corn yields were higher in the corn/leucaena intercrop (2.8 t ha^-1) than in the corn monocrop (2.5 t ha^-1). In another experiment, grain yields of corn were increased from 48.5 g plant^-1 in pure stand to 69.9-74.4 g plant^-1 in a corn/leucaena intercrop (Rosa et al., 1980).

Another forage legume of importance in the subtropics is desmodium. Most of the work has been done with desmodium/grass mixtures (Younge et al., 1974; Whitney et al., 1967; Whitney and Green, 1969; Whitney, 1970). No study has been reported where desmodium was intercropped with corn.

The amount of N contributed by a legume to an associated non-legume or to a subsequent crop basically depends on the N fixing ability and N requirement of the legume. The amount of N fixed by leucaena has been reported to range from 310 to 800 kg N ha^-1 yr^-1 (Brewbaker et al., 1972; Gomez and Zandstra, 1976). Most of the work on N contributions from leucaena to corn has been done by adding leucaena foliage to corn plots (Guevarra, 1976; Kang et al., 1981a, 1981b; Read, 1982; Evensen, 1983). No work has been reported on the transfer of N from leucaena to an associated corn crop or the residual N available from the root system of leucaena to the following crop of corn.

Desmodium has been found to fix as much as 381 kg N ha^-1 yr^-1and was able to transfer about 5% of its N to associated grasses (Whitney et al., 1967). Transfer of N from desmodium to associated grass was also reported to be as little as 1.66% in sand culture (Henzell, 1962) to as much as 20% to pangolagrass (Whitney and Green, 1969). An accumulation of 101 to 112 kg N ha^-l yr^-1 in soil by desmodium has also been reported (Henzell et al., 1966). No work has been reported on the evaluation of N transfer from desmodium to an associated corn crop or the residual N available to a subsequent crop of corn.

Legumes differ in their N fixing abilities and N required for their growth. Since, leucaena (tree type) and desmodium (creeping type) differ in their growth patterns, the yield performance and N

contribution to corn from these legumes may be different. No effort has been made to compare the performance of these two types of forage crop with corn. Therefore, there is need to further investigate the use of these forage legumes (leucaena and desmodium) in cropping systems with corn.

The present investigation was conducted to evaluate the yield potential and N economy of intercropping two forage legumes with corn.

MATERIALS AND METHODS

A field experiment involving intercropping of two forage legumes (leucaena and desmodium) with a main crop of coin during four consecutive growing seasons and a crop of corn following the forage legumes in season 5 was conducted at Waimanalo Research Station in very fine kaolinitic, isohyperthermic, Vertic Haplustoll soil.

Planting

Two crops of sweet corn were grown in the field to remove available N from the soil before starting the experiment. Corn (Zea mays L.) var. H 763 was grown as a main crop. Leucaena (Leucaena leucocephala (Lam.) de wit) var. Hawaiian Giant (K8) and desmodium (Desmodium intortum (Mill) Urb) var. Greenleaf were grown with or without corn in four consecutive growing seasons. In season 5, leucaena and desmodium stubble were killed by spraying a 50:50 mixture of Roundup and Diesel directly over stubble. Two weeks after spraying, legume plots were tilled and corn was planted. In addition, monocrops of corn were grown at urea-N rates of 0, 33, 67 an a 100 kg ha^-1 in each season. The experiments were arranged in a randomized block design with 4 replications.

Leucaena seeds were scarified with sulfuric acid, and then were inoculated with TAL 582 strain of Rhizobium spp. before planting in dibble tubes on March 27, 1981. Seedlings were watered regularly and a N-free plant nutrient solution was supplied to the seedlings by drenching every two weeks for about12 weeks before transplanting in the experimental plots. Desmodium seeds were inoculated with a mixture of TAL 569, TAL 667 and TAL 1147 strains of Rhizobium spp. before planting.

Planting of desmodium and transplanting of leucaena were done on June 15, 1981. Five crops of corn were planted on June 15, 1981, November 10, 1981, April 22, 1932, September 30, 1982 and February 15, 1983 In seasons 1 through 5, respectively. P as triple super phosphate and K as muriate of potash were applied at the rates 120 and 100 kg

ha^-1, respectively, for all crops in each season. N as urea was applied at four levels (0, 33, 67, and 100 kg ha^-1) only in monocrops of corn in each season. Treatments with monocrops of legumes and intercrops of legumes with corn were not supplied with N.

Leucaena and desmodium were planted at plant densities of 50,000 and 800,000 plants ha^-1, respectively, in both monocrop and intercrop. Corn was planted at a density of 53, 333 plants ha^-1 in the monocrop and 40,000 plants ha^-1 in the intercrop. Leucaena was planted in rows 100 cm apart with a within row plant spacing of 20 cm in both the monocrop and intercrop. The row spacing for desmodium was 25 cm and the plant spacing was 5 cm in both the monocrop and intercrop. Corn was planted in rows 75 cm apart in the monocrop and 100 cm apart in the intercrop, and had a plant spacing of 25 cm in both monocrop and intercrop. Planting patterns are presented in Appendix Figure l.

Weed and Insect Control

Atrazine and Lasso Preemergence herbicides were applied at the rate of 2 kg ha^-1 of each in plots of monocropped corn. In all other legume plots only Lasso was applied at the rate of 2 kg ha^-1. Weeds were also removed by hand whenever necessary.

Diazinon and Sevin (at the rate of 12 oz each in 100 gallons of water) were sprayed to control the insect, mainly Rose beetle.

Harvesting

Leucaena and desmodium were harvested at intervals of 6 to 8 weeks at heights of 50 and 5 cms, respectively. This much stubble was left for regrowth of these perennials. Leucaena anddesmodium both harvested 9 times. Harvest numbers 1 and 2 were made in season 1, harvest numbers 3 and 4 in season 2, harvest 5, 6 and 7 in season 3, and harvest numbers 8 and 9 in season 4.

Plant Height and LAI

Heights of 10 plants from each treatment were measured and the mean values were used for plant height.

Leaf area index of desmodium were measured by taking leaves from 5 plants in each of the desmodium plots, and then measuring the leaf area with a Leaf Area Meter (LIOOR-CI - 3100). In leucaena, subsampling of leaves was done and the leaf areas of these subsamples were measured. Based on the total dry matter of leaves in the whole plant, the Values from subsamples of leaves were used to calculate the leaf area in the whole plant of leucaena. The leaf area index (LAI) was calculated as leaf area pet unit area of land.

Dry Matter Yield

Grain and stover yields were measured in corn. Above ground parts of leucaena and desmodium were measured for forage yields. Total dry matter yields were calculated by the addition of all components. Yields are reported in Megagrams per hectare (Mg ha^-1), which is a metric ton or million grams per hectare.

Nitrogen Contents

Ear-leaf samples taken from corn plants at the 50% silking stage were analyzed for N content. Grain, stover, and forage samples after each harvest were analyzed for N content by the Microkjeldahl method (Bremner, 1965a), and total N yields were calculated.

Soil samples taken from individual plots, before and after each crop season, were analyzed for available NH₄-N and NO₃-N by the

Steam-distillation method (Bremner, 1965b).

Evaluation

Productivity per hectare of land was estimated by calculating land equivalent ratios (LER) for all the intercropped plots. The calculation was done as:

Corn intercrop yield Legume intercrop yield

LER = -------------------- + -----------------------

Corn monocrop yield Legume monocrop yield

A harvest index (HI) was calculated for each crop as HI = economic yield/biological yield, where grain yield was the economic yield and above ground total dry matter was used as the biological yield.

Nitrogen contributions from legumes to corn were estimated by comparing the N uptake by intercropped corn with the N uptake by monocropped corn at four levels of N.

Statistical analysis of the data included the analysis of variance, F test, Duncan’s multiple range test, simple correlation technique and regression analysis.

RESULTS AND DISCUSSION

Performance ofCorn in Intercropping

Corn responded well to increased rates of N application in seasons 1 and 3, which happened to be summer (Figure 4.1). Increases in grain yields of corn were from 0.39 to 4.28 Mg ha^-1in season 1 and from 0.55 to 4.82 Mg ha^-1 in season 3 with increased rates of N application iron 0 to 100 kg ha^-1, respectively. Response to increased rates of N by corn was poor in seasons 2 and 4, which were the winter period. Grain yields of corn increased from 0.38 to 0.57 Mg ha^-1 in season 2 and from 0.39 to 0.99 Mg ha^-1in season 4 as applied N increased from 0 to 100 kg ha^-1, respectively. The poor performance of corn during the winter (seasons 2 and 4) compared to summer (seasons 1 and 3) was due to lower solar radiation and temperature during the winter (Appendix Table 3).

Grain yields of corn intercropped with leucaena and desmodium were not significantly different from the grain yields of monocropped corn without N in seasons 1, 3 and 4 (Figure 4.2 and Appendix Table 5); however, grain yield of corn was significantly depressed in the Leucaena plot in season 2. Percentages of corn grain yields obtained with intercropping compared to monocropping (control plots) were 128 and 72% in season 1, 60 and 71% in season 2, 122 and 91% in season 3, and 102 and 118% in season 4 in leucaena and respectively (Table 4.1). Corn with leucaena seemed to do a little better than with desmodium in seasons 1 and 3 (summer), while corn with desmodium seemed to do a little better than corn with leucaena in seasons 2 and 4 (winter). However, these differences were not significant. Except in season 2, there seemed to be a slight yield advantage to corn grown with leucaena over monocropped corn without N, while except in season 4, there seemed to be no yield advantage to corn grown with desmodium over monocropped corn without N. Again, these differences were not significant.

Total dry matter yields (grain + stover) of corn in leucaena and desmodium plots were not depressed in seasons l, 3 and 4, however, total dry matter yield of corn was depressed by leucaena in season 2 (Figure 4.2).

Harvest indices of corn intercropped with leucaena and desmodium were not different from those of the control plots of corn (Table 4.2). Plant heights of corn intercropped with leucaena and desmodium were not significantly different from the plant height of monocropped corn without N in seasons 1 and 3, but were significantly higher in seasons 2 and 4 (Table 4.2).

The reduction in grain yield and total dry matter of corn grown with

CHAPTER V

EVALUATION OF LEUCAENA (Leucaena leucocephala (Lam.) de wit)

AS A GREEN LEAF MANURE FOR CORN (Zea mays L.)

INTRODUCTION

Leucaena with its capacity for fixing high amounts of atmospheric nitrogen (310 to 800 kg N ha^-1 yr^-1) and high N content (3 - 4%) in its foliage (Brewbaker et al., 1972; Gomez and Zandstra, 1976) is becoming popular for its use as green-leaf manure. Two basic types of systems involving leucaena use as a green manure are being practiced. In the first, hedgerows of leucaena are intercropped with food crops, also known as “alley cropping”, where leucaena foliage are periodically pruned and mulched or incorporated into the soil for use by the companion food crop. The second system involves sole cropping of leucaena, where leucaena foliage is cut and carried to another field where it is mulched or incorporated into the soil for use by another food crop. The latter one is also known as a “cut and carry” system.

In a corn/leucaena intercropping experiment, where leucaena foliage was incorporated into the soil, the yield of intercropped corn with leucaena incorporation was comparable to yield of corn where urea was applied at the rate of 75 kg N ha^-1 (Guevarra, 1976). In a corn/leucaena alley cropping experiment, application of 100 kg ha^-1 of fertilizer N, 10 t ha^-1 of leucaena prunings, or 50 kg ha^-1 of fertilizer N plus 5 t ha^-1 of leucaena pruning treatments produced 4.5, 3.7, and 3.5 t grain ha-¹,respectively, in contrast to 2.6 t ha^-1for the no N control (Kang et al., 1981a). Increased corn grain yields with application of leucaena pruning over control plot (no N applied) were also reported in other experiments (Kang et al., 1981b; Mendoza et al., 1981).

In cut and carry system, Read (1982) studied several important leucaena green-leaf manure management alternatives and reported that fresh-leaf application was better than dry-leaf application, incorporation of leucaena was better than mulching, and there was no difference in applying the leucaena at planting and splitting the application over time. In Hawaii, Evensen (1983) reported that incorporation of leucaena leaves was superior to mulching.

In chapter IV, where leucaena was intercropped with corn for forage purpose and leucaena prunings were not applied into the soil, N contribution from leucaena to companion corn crop was not significant. Therefore, further investigation on the use of leucaena forage as a green manure to corn crop is needed to understand the full potential of leucaena as a N source.

The main objectives of the present investigation were to : 1) evaluate the use of leucaena as a green-leaf manure in corn production, 2) compare the efficiency of leucaena green-leaf manure with urea as N sources, and 3) determine residual effects of leucaena green-leaf manure on the following crop of corn.

MATERIALS AND METHODS

A field experiment involving green manuring of leucaena to corn was conducted during two consecutive growing seasons begining June 1982 at Waimanalo Research Station in a very fine, kaolinitic, isohyperthermic Vertic Haplustoll soil.

Treatments

The experiment was arranged in a randomized complete block design with 7 treatments and 4 replications. Treatments applied were a control plot (no N applied), three levels of urea-N application (33, 67, and 100 kg N ha^-1) and three levels of leucaena-N application (47, 94, and 141 kg N ha^-1).

Planting

Two plantings of corn (var. H 763) were made in this investigation. The first planting was made on June 3, 1982 to evaluate the potential of leucaena forage as a green manure to the corn crop and the second

planting was made on September 30, 1982 to evaluate the residual effects of leucaena green manure. Spacing of 75 cm between rows and 25 cm between plants were used to give a planting density of 53,333 plants ha^-1 in both seasons.

Leucaena var. Hawaiin Giant (k8) was used as a green manure to corn. Succulent leaf and stem portions of leucaena forage were cut and carried from another field to the corn plots. Leucaena forage was chopped and then 5.78, 11.56, and 17.25 kg of chopped leucaena (air dried to 15% moisture and 2.84% N) were applied per 30 m² plot in the field for 47, 94, and 141 kg leucaena-N ha^-1, respectively. Leucaena forage was incorporated into the top 15 cm of the soil by rotary tiller one week before planting of the first crop of corn. No leucaena forage was applied to the second crop of corn.

Urea-N was applied at three levels (33, 67, and 100 kg N ha^-1)in both seasons. P as triple super phosphate, and K, as muriate of potash were applied at the rates of 120 and 100 kg ha^-1, respectively, in all plots in both seasons.

The first and the second crops of corn were harvested on September 23, 1982 and January 24, 1983, respectively. Sampling area at the time of harvest was 6.75 m² in both corn crop.

Observations

Plant heights of 10 plants from each treatment were measured after silking and mean values were used.

Grain and stover yields were measured. Total dry matter production was calculated by addition of all the components. Yields are reported in Megagrams per hectare (Mg ha^-1), which is a metric ton or a million grams per hectare.

Harvest index (HI) was calculated as:

HI = economic yield/biological yield,

where grain yield was the economic yield and the above ground total dry matter was used as the biological yield.

Ear leaf samples taken from corn plants at the 50% silking stage in each season were analyzed for N content. Grain and stover samples taken after each harvest were analyzed for N content by Microkjeldahl method (Bremner, 1965a), and total N yields was calculated. Soil samples taken from individual plots before and after each crop season were analyzed for available NH₄-N and NO₃-N by steam-distillation method (Bremner, 1965b).

Nitrogen recoveries from the applied urea-N and leucaena-N were calculated in both seasons as:

N uptake by plants N uptake by plants

with added N ---- with no N added

% N recovery= -------------------------------------------

Rate of N applied

Evaluation

Two methods were used to evaluate the potential of leucaena forage as green manure to corn: 1) by comparing corn grain yields in leucaena-N vs urea-N treatments, and 2) by comparing N uptake by corn plants in leucaena-N vs urea-N.

For statistical analysis an analysis of variance of the data was conducted. F tests, Duncan’s multiple range tests, simple correlation techniques and regression analysis were used wherever necessary.

RESULTS AND DISCUSSION

Performance of Corn in Season 1

Plant heights of corn increased with increasing rates of urea-N and leucaena-N (Table 5.1). Plant height of corn at leucaena-N application of 47 kg ha^-1 was comparable with plant height obtained at urea-N application of 33 kg ha^-1, and plant heights of corn at leucaena-N rates of 94 and 141 kg ha^-1 were comparable with plant height obtained at urea-N rate of 67 kg ha^-1.

Corn grain yields increased from 0.51 to 3.72 Mg ha^-1 as urea-N rates were increased from 0 to 100 kg N ha^-1 (Table 5.1). Corn grain yield (1.03 Mg ha^-1) obtained at leucaena-N rate of 47 kg N ha^-1 was higher than that of control plot (0.51 Mg ha^-1). Corn grain yields obtained at leucaena-N rates of 94 and 141 kg N ha^-1 were comparable with grain yields obtained at urea-N rates of 33 and 67 kg ha^-1, respectively. Total dry matter of corn had the same trend as observed for corn grain yield. Harvest indices of corn increased with increasing rates of urea-N. Harvest indices of corn from leucaena incorporated plots (0.20 - 0.27) were comparable with the harvest index (0.26) of corn from the plot where urea-N was applied at the rate of 33 kg N ha^-1.

Leucaena green manuring at the rates of 47, 94, and 141 kg N ha^-1 produced corn grain yields equivalent to urea-N application rates of 18, 35, and 58 kg N ha^-1,respectively (Table 5.1 and Figure 5.1). The efficiency of leucaena green manures to produce corn grain as compared to urea-N applications were found to be 37 to 41% in season 1. In other words, corn with application of 100 kg of leucaena-N might be able to produce grain

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