Growth, Yield and Nodule Activity of Mungbean Intercropped with Maize and Cassava

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1 J Sci Food Agric 1994,66, Growth, Yield and Nodule Activity of Mungbean Intercropped with Maize and Cassava Ravi Sangakkara Faculty of Agriculture, University of Peradeniya, Peradeniya, Sri Lanka (Received 4 May 1994; accepted 11 July 1994) Abstract: A field study evaluated the influence of maize (Zea mays) and cassava (Manihot esculenta) on the growth, yield and nodulation parameters of individual plants of mungbean (Vigna radiata), established as an intercrop. The two systems were managed in a similar manner. Germination, establishment and growth of plants, and yield parameters of mungbean within the maize crop were reduced to a greater extent than that of plants grown with cassava. In addition, in both systems, growth and yields of mungbean plants in close promixity to the nonlegume were suppressed to a greater degree than in plants in the centre rows. In contrast, nodulation and nodule activity of plants in close promixity to maize or cassava was higher than in that of centre rows. The study revealed that shading of mungbean plants in close proximity to maize and cassava does not reduce nodule activity. While competitive relationships between the non-legume and mungbean could affect the growth and yields of the legume plants in close promixity, the greater utilisation of nitrogen by the non-legume is suggested to be the causal factor for increased nodule activity. Key words: intercropping, mungbean, growth, yield, nodule activity. INTRODUCTION Intercropping of different species is a common practice in the tropics and subtropics, especially in smallholder farming systems. This system of crop husbandry is primarily used to obtain a greater productivity per unit land area by exploiting scare resources more efficiently. The system also develops the complementary characteristics of the intercropped species (Beets 1982). The most common crop combinations in tropical intercropping systems are mixtures of legumes and nonlegumes (Wood and Myers 1987; Fujita et a1 1990). Inclusion of legumes enhances crop and nitrogen yields of the non-legumes (Barker and Blarney 1985; Wood and Myers 1987). Increases in soil microorganisms and mineral nitrogen in the plant rhizosphere has also been reported (eg Singh et al 1986) in these systems. However, improvements in the relative productivity of component species in these intercropping systems are generally attributed to the ability of the legume to fix 417 J Sci Food Agric /94/$ SCI. Printed in Great Britain atmospheric nitrogen (Rerkasem et al 1988), a nutrient often limited in tropical agriculture (Mengel and Kirkby 1987). In upland intercropping systems, legumes are planted bet ween rows of non-legumes. The competitive effects between individual plants of the two species are not uniform due to the presence of many rows of the legume within the non-legume population. Thus, legume plants in close proximity to the non-legume could be subjected to a greater competitive stress than plants in the central rows. This could affect growth and yields of the legume, and most importantly, the nitrogen fixing capacities. Studies have quantified both yields (eg Sangakkara 1988) and nitrogen fixation of legumes in intercropping systems (eg Agboola and Fayemi 1972; Nambiar et al 1983, Peoples and Herridge 1990). However, information on the growth of individual legume plants within intercropping systems or the effects of different nonlegumes on the symbiotic activity of the legume is not readily available. Thus, a field study was conducted to

2 418 R Sangakkara test the effect of different non-legume species on growth, yields and nodule activity of individual plants of mungbean (Vigna radiata L Wilczek), a popular food legume of the tropics, when established as an intercrop. The non-legumes selected were maize (Zea mays L) and cassava (Manihot esculenta L Cranz), which are also two important staple food crops in the tropics. consecutive days using a Licor Photometer (Licor Instruments, NE, USA). Thereafter, 15 adjacent plants from each row were marked, for the measurement of yield components and seed yields (at 18% moisture). The data obtained was analysed using a general linear model, as described by Gomez and Gomez (1981) to determine the significance of observed differences. MATERIALS AND METHODS The study was carried out at the experimental station of the University of Peradeniya, Sri Lanka (7" N, 81" E, 480 m above sea level) over the planting season beginning in October The climatic conditions during the period of study were: rainfall 1060 mm, mean daily temperature 29.4" 2.4"C; and a h daylength. The soil of the site was an alfisol, with a ph (1 : 2.5 KCl) 6.41, total N content of 0.31% and CEC of 2 meq per 100 g soil. The selected crops and varieties were maize (variety Bhadra), cassava (variety CAR1 555) and mungbean (variety MI 5). Uniform seeds of maize (germination 91.5%) and cuttings of cassava were planted in rows in well-prepared seedbeds. The species were established in separate plots, and the spacings used were 80 cm between rows, with a within row distance of 80 cm for cassava and cm for maize. Mungbean seeds (germination 89.2%) were planted 5 days later within the rows of the two non-legume species. The spacing used for the rows were 10, and cm from the nonlegume, with a within row spacing of 10 cm. A monoculture of mungbean was also established at the same spacing for comparison. The experimental design used was a randomised block design with five replicates. Individual plot size was 8 x 6 m. Maize and cassava were fertilised with kg N, 45 kg P,05 and 60 kg K,O ha-', at planting. This mixture was applied to the rows of these two crops. The fertiliser applied to mungbean at planting was 10 kg N, 45 kg P205 and 60 kg K20 ha-'. This was broadcast between the rows of the non-legume. Weeding was carried out at 15 and 30 days after planting of the mungbean. Irrigation was not required. Germination and establishment of mungbean was determined within fixed quadrats of 2 x 3 m. From 10 days after germination, five plants of mungbean were carefully removed from each row of all plots and dried at 80 C to a constant weight. This data was used to calculate the relative growth rates over the vegetative phase (V2-V6) as described by Fageria (1992). At 50% flowering (R3), seven plants of mungbean were carefully removed from each row in all replicates for the determination of nodule numbers, acetylene reduction activity (Hardy et al 1968) and nodule dry weights. At the same time, radiation received by each row of mungbean within the intercrops was also measured at 12:OO h for 5 RESULTS AND DISCUSSION Germination and establishment of mungbean were affected by the non-legumes and the distance of planting from these species (Table 1). The interaction between these two factors was also significant, thus illustrating the influence of both parameters in determining germination and establishment of the intercropped species. In both intercropping systems, germination of seeds and establishment of young seedlings was lowest in the row sited 10 cm from the main crop. With increasing distances, these parameters were enhanced significantly, especially when mungbean was planted with cassava. Maize suppressed germination and establishment of mungbean to a greater extent than cassava (Table 1). This difference is primarily due to the reduction in germinability and establishment of mungbean in the rows nearest to the main crop. For example, germination of mungbean in the row sited 10cm from maize is 13% lower than that in the similar row of the cassava plots. This phenomenon is considered a resultant effect of the more rapid early growth of maize seedlings when compared with that of cassava propagules. The rapid growth of the maize seedling could deplete resources required for the mungbean seedling, thus reducing the population of legume plants. Growth of mungbean is also affected by the nonlegume and the distance from the main crop. This is clearly exemplified by the ratios of relative growth rates of plants in the different rows in the intercropped plots to that of the sole crop (Table 1). The adverse impact of maize on these ratios is significantly greater than that of cassava. This again could be attributed to the greater competitive effects and exploitation of resources by maize, which has a greater growth potential than most crop plants of the tropics (Fageria 1992). The shorter lifespan of maize (4 months) when compared to that of cassava (10 months) could also influence this phenomenon. Light interception patterns also illustrate the greater shading effect of maize (a % reduction in incident radiation) to mungbean plants when compared to that of cassava (a 24% reduction). Relative growth rate ratios of mungbean in different rows within the two intercropping systems also highlights this phenomenon clearly. The reduction in ratios of mungbean plants in close promixity to the maize in significantly lower than in plants grown at the same spacing with cassava. While the ratio increases with

3 Growth, yield and nodulation of intercropped 419 TABLE 1 Germination, emergence and growth rates of mungbean as affected by distance from main crop Main crop from Germination Establishment RGR Ratio" main crop (cm) ("/.I ("/.I Cassava 10 Maize OOo a RGR ratio = RGR of mungean plants when intercropped/rgr of mungbean plants when grown as a sole crop increasing distances, especially when intercropped with maize, mungbean plants established at and cm from cassava rows have similar ratios. This again illustrates the greater competitive effects of maize on the intercropped mungbean than cassava, which could be associated with the differences in growth patterns of these two species (Sangakkara 1988). Results of yield components and yields of mungbean plants when intercropped with maize and cassava and as a sole crop (Table 2) follow that of germination and relative growth rate ratios. Mungbean plants established with maize have a lower number of flowers. This could be due to the greater light interception by the maize canopy, as shading reduces flowering and enhances dehiscence in mungbean (Lawn and Ahn 1985), along with the poor growth of plants (Table 1). Mungbean plants grown at a distance of 10 cm from maize have the lowest number of flowers per plant when compared with the sole crop. Although the flower numbers increase with distance, the difference are much greater than in plants established with cassava. This again could be related to the greater competitive effects of maize on mungbean, which reduces growth (Table l), thus affecting flowering. There is no interaction between the main crop and planting distance on pod numbers and 100 seed weights (Table 2). However, plants of mungbean in close proximity to the maize have the lowest numbers of pods and seed weights. This again could be directly associated with the competitive effects between the species in the two intercropping systems. The impact of the effects of the main crops and plant distances is best reflected in seed yields per plant (Table 2). Plants established as a sole crop have the highest yield, thus confirming earlier studies (eg Rerkasem and Rerkasem 1988) of yield reductions in legumes when TABLE 2 Effect of planting distance from main crop on yield components of mungbean Main crop from main crop Flowers per plant Pods per plant 100 seed wt (9) Yield per plant (9) Cassava Maize

4 420 R Sangakkara intercropped, due to competitive effects. yields of plants grown with cassava are lower than that of the sole crop. However, the greatest reduction in mungbean yields is due to maize. This clearly shows that different non-legumes affect growth and yields of intercropped mungbean differently, as suggested by Miah and Carangal (1980) and Sangakkara (1988). The causal factor for low yields of mungbean when intercropped with maize in relation to those intercropped with cassava is clearly presented in per plant yields in different rows. Yields of plants in close proximity to maize and cassava rows in some 33 and 28% lower than those of the monoculture. Although per plant yields increase with increasing distance from the main crop, the increments in the maize-mungbean system is lower than that of plants grown with cassava. This could phenomenon could also be identified with the light availability, although root interactions cannot be ignored. Nodulation of legumes, which determines biological nitrogen fixation depends on several factors, among which species, plant densities and competitive effects play an important role (Ofori and Stern 1987; Fujita et al 1992). Some of these aspects are highlighted in the present study (Table 3), along with the nodule activity of single plants of mungbean when grown at different distances from maize and cassava. Nodulation of mungbean at flowering is affected by the non-legumes and the distance of planting from these crops. In overall terms, nodulation parameters measured in mungbean is enhanced when grown with maize. This could be due to the greater demand for soil nitrogen by maize when compared with cassava, which in turn could reduce the nutrient from the rhizosphere of the legume. Thus, the legume meets the nitrogen requirements by increased symbiotic activity. In contrast, the slower growing cassava plants would place a lower demand for nitro- gen. Thus a greater quantum of the nutrient would be available for the legume. As fertiliser nitrogen in the rhizosphere reduces biological activity of legumes (Nambiar et al 1983; Ofori and Stern 1987), this phenomenon could be considered a major causal factor for the above observation. Nodule activity is also dependant on the photosynthetic capacity of a plant. Thus shading could reduce nodule activity of legumes, due to reductions in the photosynthate supply (Fujita et al 1992). However, in the present study, mungbean plants in close proximity to the non-legume have greater nodule activity than plants in the centre rows. This implies that shading levels in this study has little influence on nodule activity. Increased nodule numbers, dry weights and specific activity could be considered a causal factor of the lack of nitrogen in the rhizosphere. This would induce the legume to meet nitrogen requirements by increased symbiotic activity, irrespective of the shading regime. The greater activity of nodules in mungbean plants in close proximity to maize rows when compared to those planted inbetween cassava which intercepts a lower quantum of radiation also supports this hypothesis. CONCLUSIO Intercropping reduces yields of legumes (Fujita et al 1990, 1992), although total productivity of mixed cultures often exceed that of the respective monocultures (Fageria 1992). The yield reduction of the legume is attributed to competition effects, and the non-legume has a significant influence on this parameter. This study clearly reveals that maize has a greater adverse impact on growth, yields and nodulation of mungbean than cassava. However, the adverse impact of the nonlegume is not similar on all plants in the intercropping TABLE 3 Nodulation and nodule activity of mungbean as affected by distance from main crop, at 50% flowering Main crop from Nodules per plant Nodule dry wt Specific activity main crop (cm) (rng per plant) (pmol C,H, per plant per hour) Cassava 10 Maize

5 Growth, yield and nodulation of intercropped 42 1 systems. Mungbean plants in close proximity to the non-legume are affected to a greater extent. The impact on mungbean plants established in close proximity also differs according to the non-legume, which determines the overall productivity of the system. Thus, although the mechanisms of this phenomenon were not elucidated, the results suggest a greater impact of soil and nutrient parameters in determining the growth and yields of the legume. Nodulation characteristics suggest the impact of nitrogen, which is easily removed from the rhizosphere, and further studies are warranted for the confirmation of causal mechanisms. ACKNOWLEDGEMENT Gratitude in expressed to Mr N Gamage and Ms N Wijesinghe for research assistance and determination of nodule activity respectively. The study was partially supported by a grant from the University of Peradeniya. REFERENCES Agboola A A Fayemi A A 1972 Fixation and extraction of nitrogen by tropical legumes. Agron J Barker C M, Blamey F P C 1985 Nitrogen fertilizer effect on yield and nitrogen uptake of sorghum and soybean in sole and intercropping systems. Field Crops Res Beets W C 1982 Multiple Cropping and Tropical Farming Systems. Westview Press, Bolder, Co, USA. Fageria N K 1992 Maximizing Crop Yields. Marcel Dekker Inc, New York, USA. Fujita K, Ogata S, Matsumoto K, Masuda T, Ofoso-budu K G, Kuwata K 1990 Nitrogen transfer and dry matter production in soyabean and sorghum mixed cropping systems at different population densities. Soil Sci Plant Nutr Fujita K, Ofoso-budu K G, Ogata S 1992 Biological nitrogen fixation in mixed legume cereal cropping systems. Plant and Soil Gomez K A, Gomez A A 1981 Statistical Procedures for Agricultural Research with Emphasis on Rice. IRRI, Philippines. Hardy R W F, Holsten R D, Jackson E K, Burns R C 1968 The acetylene ethylene reduction assay for N, fixation- Laboratory and field measurement. Plant Physiol Lawn R J, Ahn C S 1985 Mungbean, in Green legume crops, ed Summerfield R J, Roberts E H, Collins, UK, pp Mengel K, Kirkby E A 1987 Principles of Plant Nutrition. International Potash Institute, Bern, Switzerland. Miah M N I, Carangal V 1980 Evaluation of mungbean cultivars under monoculture and intercropping systems. IRRI Newsletter Nambiar P T, Rao M R, Reddy M S, Floyd C, Dart P J, Willey R 1983 Effect of intercropping on nodulation and N fixation by groundnut. Exper Agric Ofori F, Stern W R 1987 Cereal legume intercropping systems. Adu Agron Peoples M B, Herridge D F 1990 N fixation by legumes in tropical and subtropical agriculture. Adu Agron Rerkasem B, Rerkasem K 1988 Yields and nitrogen metabolism of intercropped maize and ricebean. Plant and Soil Rerkasem B, Rerkasem K, Peoples M B, Herridge D F, Bergerson F J 1988 Measurement of N fixation in maize ricebean intercrops. Plant and Soil Sangakkara U R 1988 Mungbean in annual mixed cropping systems. In Mungbean, ed Shanmugasundaram S. AVRDC, Taiwan, pp Singh N B, Singh P P, Nan K P 1986 Effect of legume intercropping on enrichment of soil N, bacterial activity and productivity of associated maize crops. Exper Agric Wood I M, Myers R J K 1987 Food legumes in the nitrogen cycles of farming systems. In: Food Legume Improvement for Asian Farming Systems (Publication 18), ed Wallis E S et al. ACIAR Canberra, Australia, pp