Nitrogen dynamics and crop growth on an Alfisol and a Vertisol under a direct-seeded rainfed lowland rice-based system

Rice (Oryza sativa L,) followed by chickpea (Cicer arietinum L.) or a fallo w is one of the predominant cropping systems in the rainfed lowlands of Ind ia, Crop rotation experiments over 3 years (1996-1998) to quantify N supply and demand under rainfed lowland rice-chickpea and rice-fallow cropping sy stems on a loam Alfisol and a clay Vertisol in Raipur, India were conducted under direct-seeded rice culture. The rice growth, yield, development and N accumulation were affected most by N rates (0, 40, 80, 120 kg ha(-1)) fol lowed by cropping system (rice-chickpea, rice-fallow) and soil types (Alfis ol, Vertisol). The incorporation of chickpea in the cropping system helped in accumulating a greater amount of soil N than fallow. The rice yield, dry matter and N accumulated were significantly higher in rice-chickpea than r ice-fallow systems on both soils and in all years. The lowest rice yields w ere recorded in 1997 due to unfavorable rainfall distribution. The total ra infall was the highest in this season, but most of it occurred during a sho rt period at an early growth stage. The post-heading rains were lowest in t his season and resulted in the lower rice yield as compared with that of 19 96 and 1998. This indicates the significance of rainfall distribution in co ntrolling yield in a rainfed environment. The rice yields were lower on Ver tisol than Alfisol during periods of drought. The performance of chickpea w as also better in Alfisol as compared with that in the Vertisol due to its better soil physical attributes. The residual effect of N applied to the pr eceding rice crop was non-significant on all yield, growth and N accumulati on parameters of chickpea. The N balance computed from the top 70 cm soil l ayers indicated less N loss in the rice-chickpea system as compared with th at in rice-fallow. The recovery efficiency at the highest N rate (120 kg N ha(-1)) was higher for the rice-chickpea (57-61%) than that of rice-fallow (49-53%) system. The improved N balance for rice-chickpea system from third year onwards was due to switch to dry seeding and improved soil N status. The inclusion of legume and the effective capture of biologically fixed N a nd soil N through direct-seeded rice system in rainfed lowlands may help in improving the rice yield of resource poor farmers. (C) 2001 Elsevier Scien ce B.V. All rights reserved.