Productivity of maize-legume intercropping systems under rainfed situation

The present experiment was carried out to study the intercropping effect of green gram, black gram, soybean, groundnut and red gram with maize during kharif season of 2009 and 2010. Treatments consisted of sole crop of maize [rows spaced 60 cm apart (M1) and paired rows (30 cm apart) spaced at 90 cm apart (M2)], green gram (GG), black gram (BG), soybean (SB), groundnut (GN), and red gram (RG); intercropping of M1+GG, M1+BG, M1+SB, M1+GN and M1+RG with 1:1 and M2+2GG, M2+2BG, M2+2SB, M2+2GN and M2+2RG with 2:2 row proportions. Maize equivalent yield was always higher in all the intercropping situations as compared to pure stand yield of maize. The highest maize grain yield was obtained with maize + green gram intercropping (2783.11 kg ha) in 1:1. The highest maize equivalent yield was observed with maize + red gram (5270.46 kg ha) in 2:2 intercropping system. Values of land equivalent ratio, relative value total, relative net return and area time equivalent ratio were greater than unity and differed significantly in between both the groups of 1:1 and 2:2 proportions of intercropping. Highest gross and net return of Rs.55191.60 ha and Rs.39950.30 ha respectively was recorded in maize+red gram (2:2) intercropping.


INTRODUCTION
Intercropping is gaining popularity day by day among small growers as it provides yield advantage as compared to mono cropping through yield stability and fulfilling diversified domestic needs.Cereal-legume intercropping facilitates to maintain and improve soil fertility (Andrews, 1979).Intercropping is advocated due to its benefits for yield increase (Chen et al., 2004), conserving soil, control of weeds, control legume root parasite infections and high quality fodder.Cereal-legume intercropping plays an important role in subsistence food production in developing countries, especially in situations of limited water resources (Tsubo et al., 2005).Maize based intercropping system with legume helps in improving soil health as well as yield of main crop (Beedy et al., 2010).Maize-legume intercrops yielded more and were associated with less risk than the maize-legume rotations (Kamanga et al., 2010).Maize in association with legumes gives higher total yield and net return (Patra et al., 2000).Hence, the present investigation was carried out to evaluate intercropping advantages over the respective sole crop of maize with different legumes in different sowing proportions.

MATERIALS AND METHODS
A field experiment was conducted in humid tropics of Nadia, West Bengal during the Kharif seasons of 2009 and 2010.The experimental site was situated at approximately 22º56´N, 88º32´E and at an altitude of 9.75 m above mean sea level.The soil was typical gangetic alluvium with sandy-loam in texture.The soil leads to almost neutral pH (6.8) and with 0.051% nitrogen, 18.79 kg ha - 1 available P and 90 kg ha -1 K.The experiment was laid out in an Augmented Randomized Block Design (RBD) having 17 treatment combinations replicated thrice with the plot size of 5.4 x 4 m.Treatments consisted of sole crop of maize (rows spaced 60 cm apart (M 1 ) and paired rows (30 cm apart) spaced 90 cm apart (M 2 )], green gram (GG), black gram (BG), soybean (SB), groundnut (GN), and red gram (RG), intercropping of M 1 +GG, M 1 +BG, M 1 +SB, M 1 +GN and M 1 +RG with 1:1 and M 2 +2GG, M 2 +2BG, M 2 +2SB, M 2 +2GN and M 2 +2RG with 2:2 row proportions.The recommended dose of fertilizer for sole maize (80:40:40 kg N, P 2 O 5 and K 2 O ha -1 ) and legumes (20:40:20 kg N, P 2 O 5 and K 2 O ha -1 ) were applied separately.

Yield attributes
An increasing trend was observed with respect to the number of cobs plant -1 , number of grains cob -1 in intercropped maize due to the development of both temporal and spatial complementarity as a result of which there was no competition for nitrogen and there was a possibility of current transfer of fixed nitrogen to the cereal crop like maize, however, no significant change in 1000 grain weight was noticed (Table 1).There was decreasing trend of percentage of barren stalk in all the intercropping situations.Patra et al. (1999) reported increased number of cobs plant -1 and grains cob -1 due to maize legume intercropping, however, 1000 grain weight of maize was not significantly influenced but there was an increasing trend.
Number of pods plant -1 and seeds pod -1 in green gram, black gram, soybean and groundnut were significantly reduced due to intercropping.All the intercrops grown Kheroar and Patra 1611 with maize were shorter in height and could utilize lower percentage of incoming solar radiation.Red gram was least affected due to its longer duration and taller stature (Table 2).Sole legumes always obtained higher 1000 seed/kernel weight than intercropped legumes though they were statistically at par.

Maize grain yield
Maize when planted with 60 cm row spacing always recorded higher grain yield as compared to paired rows spaced 90 cm apart both as sole crop as well as intercrop (Table 3).Grain yield of maize was increased when intercropped with legumes like green gram, black gram and soybean.The yield advantage of maize in intercropping systems with legumes probably occurred from the difference in the timing of utilization of resources by the different crops from different soil layers, especially during peak vegetative and reproductive stages of growth, thus resulting in both temporal and spatial complementarities.Also, the increase in grain yield of maize might be resulted from maize-legume association due to symbiotic nitrogen fixation by legumes and current transfer of nitrogen to the associated maize plants.In addition, there was bonus yield from legume component, which corroborated the findings of Rana et al. (2001).A decreasing trend in maize grain yield was recorded when intercropped with red gram and groundnut in both the proportions of sowing.

Intercrop yield
Yield of intercrops were reduced due to intercropping with maize (Table 2).Actual yield was slightly higher at 2:2 proportion of sowing than 1:1 proportion due to receipt of higher amount of solar radiation.Yield was mostly affected in the short statured under sown leguminous crops.Tall growing maize plants shaded the leguminous crops and the main reason for reduction in yield was probably due to the receipt of lower amount of incoming solar radiation which affected the rate of photosynthesis and thereby translocation of photosynthates from source to sink.Relatively tall growing crop like red gram was less affected with respect to receipt of incoming solar flux.Similar results were also obtained by Mandal and Mahapatra (1990), Patra et al. (1999) and Patra et al. (2000).

Combined yield
Combined yield was always higher in intercropping situations both in 1:1 and 2:2 proportions of planting than mono cropping (Table 3).It might be attributed due to the inclusion of yield of maize with some yield of legumes.In maize legume association, maize was benefitted by nitrogen fixation of intercropped legumes.

Maize equivalent yield
Maize grain equivalent yield (Table 3) was recorded to be higher in all the cases of intercropping with respect to pure stand yield of maize which corroborated the findings of Patra et al. (1999Patra et al. ( , 2000)).The highest maize grain equivalent yield was obtained in maize + red gram (2:2) intercropping (5270.46kg ha -1 ) due to higher yield and price of red gram.

Aggressivity and Competitive ratio
Aggressivity values were positive (+ve) in maize which obviously indicated that maize was the dominant crop, whereas the associated intercrops appeared to be the dominated ones having negative (-ve) values (Table 4).
Between the two spatial arrangements, 1:1 proportion of intercropping resulted in higher values of aggressivity which denoted higher interspecific competition.Likewise, competitive ratio for maize was always higher as compared with the associated intercrops and higher competitive ratio of maize was observed at 1:1 proportion of intercropping than 2:2 proportions.Being a C 4 plant, maize appeared to be more competitive and the subsidiary intercrops were found to be less competitive with respect to utilization of available resources.Among the intercrops, red gram was more competitive and offered the highest competition to maize in both the proportions of sowing.Similarly, Sawargaonkar (2008) reported that the maize-based intercropping systems were more remunerative than sole maize; Maize + black gram and maize + green gram were superior to maize + soybean for grain yield and parameters related to competitive ability.

Land equivalent ratio
LER values were always recorded to be higher than unity signifying yield advantages of intercropping over monoculture (Table 4).Yield advantages occurred due to the development of both temporal and spatial complementarities.The highest value of LER (1.418) was obtained from maize + black gram (2:2) intercropping which was closely followed by maize + green gram (2:2) intercropping (1.417).Sharma and Behera (2009) reported that, land equivalent ratio and other competitive functions were favourably influenced with intercropped maize + green gram and maize +cowpea.

Area time equivalent ratio
ATER values were also greater than unity in all the cases of intercropping.ATER values, similar to LER, were higher in cases of maize-legume combinations and at 2:2 proportion of sowing.So, the intercropping system was found to be advantageous in comparison to monoculture.Maize + black gram (2:2) intercropping recorded the highest ATER value (1.362), which was achieved probably due to the development of temporal as well as spatial complementarity (Table 4).The area time equivalent ratio was higher in maize + legume in 1:2 proportion than in 1:1 proportion (Mohan et al. 2005).

Land equivalent coefficient
Land equivalent co-efficient values were always recorded to be greater than 0.25 which indicated yield advantages in maize + legume intercropping situations in both the proportions of intercropping (1:1 and 2:2).The highest LEC (0.47) was recorded with maize + red gram (2:2) intercropping (Table 4).

Relative value total
The values of RVT were always greater than unity.The highest value of RVT was obtained with maize + red gram (2:2) intercropping (2.033) due to higher market price of red gram (Table 4).Maize + legume intercropping brought about higher RVT value probably due to higher combined yield in maize-legume association, which was in agreement with the findings of Patra et al. (1999).

Relative net return
It was found that growing of legumes in between the maize rows at both the sowing ratios 1:1 and 2:2 were profitable in comparison to sole cropping of maize when differential cost of cultivation was taken into consideration (Table 4).Maize + red gram (2:2) intercropping gave the highest RNR values (2.208).This might be due to the spatial as well as temporal complementarity which resulted in substantial yield advantages from intercropping.

Economic analysis
Intercropping in paired rows of maize spaced at 90 cm was advantageous than 60 cm row to row spacing of maize (Table 5).2:2 proportion of intercropping brought about higher gross returns as compared to 1:1 proportion of intercropping.
The highest gross and net return was obtained from maize + red gram (2:2) amounting to Rs. 55,191.60 and Rs. 39,950 ha -1 respectively.From the pooled data, it was observed that 2:2 proportion of intercropping always fetched net return than 1:1 proportion.It was also noticed that 2:2 proportion of intercropping always recorded higher B: C ratio than 1:1 proportion and the highest (3.65)B:C ratio was recorded in maize + red gram (2:2).Maize + groundnut (2:2) gave the highest Per day return of Rs. 259.30.Bharati et al. (2007) reported that maize based intercropping generated higher net return than sole crop of maize.Kamanga et al. (2010) opined maize + legume intercropping was more productive and remunerative as compared to sole cropping which was in close agreement with the present findings.

Conclusion
Maize when intercropped with legumes found to be beneficial and profitable.Maize-legume intercropping were found to be more advantageous (in additive series) with respect to maize grain equivalent yield and monetary returns in both the proportions of sowing (1:1 and 2:2) but 2:2 proportion was appeared to be more remunerative.

Table 1 .
Effect of intercropping on cobs plant -1 , grains cob -1 , 1000 grain weight and barren stalk percentage of maize (pooled data of 2 years).
Details of treatments are given in materials and methods; NS, Non Significant.

Table 2 .
Effect of intercropping on yield attributes and yields of associated legumes (pooled data of 2 years).
Details of treatments are given in materials and methods; NS, Non significant.

Table 3 .
Effect of intercropping on grain yield, harvest index, combined yield and equivalent yield of maize (pooled data of 2 years).
Details of treatments are given in materials and methods; NS, Non significant.

Table 4 .
Effect of intercropping on aggressivity value, competitive ratio, land equivalent ratio, area time equivalent ratio, monetary advantage, land equivalent coefficient, relative value total and relative net return of maize and associated legumes (pooled data of 2 years).

Table 5 .
Effect of intercropping on gross return, net return, B:C ratio and Per day return of maize and associated legumes (pooled data of 2 years).
Details of treatments are given in materials and methods; NS, Non significant.