EFFECT OF LEGUME-BASED CROPPING SYSTEMS ON NITROGEN MINERALIZATION POTENTIAL OF VERTISOL

The quantity and patterns of net mineralization of soil nitrogen (N) w ere studied in Vertisols under different cropping systems in the semi- arid tropical areas. Eight cropping systems were selected; three conta ined pigeonpea (PP), one contained PP and cowpea (COP), and two contai ned chickpea (CP) as legume component crops, one included sequence cro pping 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 compon ent crop increased mineralizable N(N-o) content two-fold in the soil c ompared 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 o bserved in the COP/PP intercrop, followed by sequential S+safflower (S F) system as compared to the other soils. Mineral N accumulation curve s for six soils were more accurately described by the exponential mode l than the linear model. The active N fraction (N-o/N-tot %) varied be tween 8 and 16% for different systems and a direct relationship was ob served between N-o/N-tot and total N for the soils under diverse cropp ing systems.