Nitrogen dynamics and crop growth on an alfisol and a vertisol under rainfed lowland rice-based cropping system

Crop rotation experiments were conducted over 2 years to quantify N supply-demand under rainfed lowland rice-chickpea and rice-fallow cropping systems on a loam Alfisol and a clay Vertisol in India. Significant differences among N rates (0, 40, 80, and 120 kg N ha(-1)) and soils were observed with rice for grain yield, total biomass and grain N uptake in both years. Low N response, low grain yield, low N uptake, and a short grain filling phase during the 1995 wet season was due to post-heading water stress. The stress was more pronounced on the Vertisol and at high N rates. This resulted in lower N content at maturity than at heading. The loss of biomass N from plant implied that apparent N recovery (AR) and physiological nitrogen use efficiency (PNUE) may differ significantly based on whether maximum N accumulation or total N uptake at maturity was used. Plant N recovery, both by the N difference method and N-15 technique, revealed much lower recovery of fertilizer N (21-27%) with rainfed lowland rice than with irrigated dry-season rice. The residual effect of N applied to the preceding rice crop was nonsignificant on all yield, growth, and N uptake parameters of chickpea. The performance of chickpea was better on the Alfisol than the Vertisol, principally due to soil physical attributes. The better performance and longer growth duration during 1994-1995 dry season as opposed to the 1995-1996 season was attributed to higher rainfall (92 mm versus 39 mm) and rainfall during the critical pod-filling to maturity phase. Mineralization and nitrification of N was negligible during the rice fallow period due to the dry conditions and low organic matter content. This was corroborated by the similarities in N balance between rice-chickpea and rice-fallow system. The PNUE of rice was 33 to 57 kg grain per kg N absorbed compared with 25 to 27 kg grain per kg N absorbed of chickpea, owing mostly to higher N concentration of chickpea grain and the higher energy cost due to biological N fixation, (C) 1999 Elsevier Science B.V. All rights reserved.