Effect of crop residue management on nitrogen dynamics and balance in a lowland rice cropping system

Abstract

Two field experiments were conducted in a rice–fallow–rice cropping sequence during consecutive dry and wet seasons of 1997 on a Fluvic Tropaquept to determine the fate and efficiency of broadcast urea in combination with three residue management practices (no residue, burned residue and untreated rice crop residue). Ammonia volatilization losses from urea (70 kg N ha−1) broadcast into floodwater shortly after transplanting for 11 d were 7, 12 and 8% of the applied N from no residue, burned residue and residue treated plots, respectively. During that time, the cumulative percent of N2 + N2O emission due to urea addition corresponded to 10, 4.3 and nil, respectively. The 15N balance study showed that at maturity of the dry season crop, fertilizer N recovery by the grain was low, only 9 to 11% of the N applied. Fifty to 53% of the applied 15N remained in the soil after rice harvest, mainly in the upper 0–5 cm layer. The unaccounted for 15N ranged from 27 to 33% of the applied N and was unaffected by residue treatments. Only 4 to 5% of the initial 15N-labeled urea applied to the dry season rice crop was taken up by the succeeding rice crop, to which no additional N fertilizer was applied. Grain yield and N uptake were significantly increased (P=0.05) by N application in the dry season, but not significantly affected by residue treatments in either season.