Effect of legume-based cropping systems on nitrogen mineralization potential of Vertisol

The quantity and patterns of net mineralization of soil nitrogen (N) were studied in Vertisols under different cropping systems in the semi-arid tropical areas. Eight cropping systems were selected; three contained pigeonpea (PP), one contained PP and cowpea (COP), and two contained chickpea (CP) as legume component crops, one included sequence cropping with nonlegumes during the rainy and postrainy seasons, and one system was kept fallow (F) during the rainy season and sown to sorghum (S) during the postrainy season. Cropping systems with PP as a component crop increased mineralizable N(N_o) content two-fold in the soil compared with fallow + sorghum (F+S)–F+S system. The N mineralization rate constant (k) was not significantly affected by previous cropping history of the soil; however, a numerically higher rate constant was observed in the COP/PP intercrop, followed by sequential S+safflower (SF) system as compared to the other soils. Mineral N accumulation curves for six soils were more accurately described by the exponential model than the linear model. The active N fraction (N_o/N_tot %) varied between 8 and 16% for different systems and a direct relationship was observed between N_o/N_tot and total N for the soils under diverse cropping systems.ICRISAT JA (1638)