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Abstract: Intercropping system of cereals with legume is common in semi-arid tropics of India. However, little attention has been paid to assessing nutrient competition in the system. Seasonal changes in relative dry matter yield (RDY), relative nitrogen yield (RNY), relative phosphorus yield (RPY) and relative potassium yield (RKY) are useful indices to estimate the N, P and K status in intercropping system. The competitive effect of soybean (Glycine max L.) in association with sorghum (Sorghum bicolor L. Moench) was assessed using these indices under six nutrient treatments (0, 75% NPK, 100% NPK, 75% NPK+5Mg farmyard manure, 75% NPK+5Mg phosphocompost and 75% NPK+1.5Mg poultry manure) from a 5-year field experiment conducted in a N and P deficient Vertisol of Central India. The RDY and RNY of sorghum were greater than the values of RDY and RNY of soybean indicating inter-species competition for N between component crops, peak competition being at 80 days after sowing (DAS). Using the concept of RDY and RNY, it was observed that having coincided the maturity period and peak demand for N of both the crops, soil N was exhausted by sorghum because of its strong competitive ability and N was liming for soybean at 80 DAS. Strong competitive ability of sorghum was also evident from higher biomass, root mass, root length density and contribution to the mixture yield. Once sorghum entered its maturity phase, its competitive effect on soybean was greatly reduced. Competition for P between two species is more prominent up to 60 DAS and P was not limiting to none of the species after 60 DAS as the RPY values were equal to corresponding RDY values. Based on RKY value, none of the component species suffered from K deficiency at any stage even if it was not applied. This implied that competition exists for soil N and P but not for K up to 60–80 DAS in soybean/sorghum intercropping system. The result showed that competition between two crops measured in terms of RNY, RPY and RKY under organic-fertilizer was less; however, recorded higher soybean equivalent yield and monetary advantage index than inorganic-fertilizer. The study thus suggests that in soybean/sorghum intercropping system to minimize competition between two crops in N and P deficient Vertisol, application of 75% NPK+FYM/poultry manure/phosphocompost is a viable nutrient management option. [Copyright &y& Elsevier]

Abstract: Opinions differ on the necessity of deep tillage for sustaining crop productivity in the rainfed Vertisols of the semi-arid tropics of central India. We conducted a field experiment for 3 years (2000–2002) with a factorial combination of three cropping systems (sole soybean, sole pigeonpea and soybean/pigeonpea intercropping in 2:1 row ratio) and three tillage practices (conventional, conventional+subsoiling in alternate years and conventional+subsoiling every year). Objectives were (i) to examine the effect of subsoiling Vertisols on sustaining yield of soybean/pigeon pea intercropping, and (ii) to assess the frequency of subsoiling for realizing maximum yield and profit. Though there was a reduction in growth and yield of intercrops, higher soybean equivalent yield (SEY) and area-time equivalent ratio (ATER) value in soybean/pigeonpea intercropping system as compared to sole soybean had a yield advantage. The average yield advantage in intercropping system was 60% higher than that from sole soybean. The yield advantage of intercropping system in terms of ATER was 7% greater with subsoiling than conventional tillage. The yield response to subsoiling was consistent over the period and on an average, subsoiling increased yield by 20%. The effect was associated with improved water storage and root length density. However, with respect to energy use efficiency and profit, the effect of subsoiling was comparable to conventional tillage. The variation in net return and benefit:cost ratio in subsoiling every year and subsoiling in alternate years in sole soybean and soybean/pigeonpea intercropping was not significant. However, in sole pigeon pea subsoiling every year out-yielded subsoiling in alternate years. The interactive effect of subsoiling and intercropping increased the yield by 21–25%. Thus, under rainfed cropping where drought of unpredictable intensity and duration is a prevailing feature, soybean/pigeon pea intercropping could be a promising option, especially when combined with subsoiling in alternate years. [Copyright &y& Elsevier]

Abstract: Low native nitrogen (N) and phosphorus (P) coupled with imbalanced nutrient application is a major constraint limiting productivity of intercropping systems on Vertisols of the semi-arid tropical India. In a 3-year field experiment competition behaviour of component crops for nutrients use in soybean/pigeonpea intercropping system was assessed based on relative yield (RY), relative nitrogen yield (RNY) and relative phosphorus yield (RPY) under three nutrient levels (0 NPK, 100% NPK (N:P:K=30:26:25kgha−1) and 100% NPK+4t FYMha−1). The result showed that before soybean harvest, the RY and RNY of soybean were greater (1.0) than the corresponding values of RY and RNY of pigeon pea (0.6). This implied that competition exists for soil N between the component crops during the first half of the cropping system. It was observed that soybean harvest did not coincide with peak flowering of pigeonpea, the stage when biological nitrogen fixation (BNF) was maximum. Thus, BNF dependency of pigeonpea was low before soybean harvest and the plants suffered from N deficiency more when no fertilizer-N was applied and diminished at a high-N level. Pigeon pea attained its peak flowering after the harvest of soybean and increased its dependency on BNF when soil N was exhausted by soybean. Thus, after the harvest of soybean, RY and RNY of pigeon pea gradually increased and approached 1.0 at maturity at all nutrient levels. The RPY values showed that phosphorus was not the limiting factor to any of the crop in the system even if it was not applied. The study thus suggests that in the soybean/pigeonpea intercropping system, N is a limiting factor for growth of pigeonpea intercrop during the first half of its growth and application of 100% NPK (30kg N)+4t FYM could meet N demand of pigeonpea in N deficient soils as this nutrient management option gave higher yield, root length density and profit under soybean/pigeonpea intercropping system than 100% NPK and control. [Copyright &y& Elsevier]