Effect of Crop Residue Management on Nitrogen Loss and Balance from Urea in a Lowland Rice Cropping system

Abstract

Field experiment were conducted in a rice-follow-rice cropping sequence during consecutive dry and wet seasons of 1997 a tthe suphanburi Rice Experiment station on a Phimai soil (Vertic Tropaquepts) to determine the fate and efficiency of broadcast urea in combination with three crop residue management practices as no residue, burned residue and untreated rice crop residue which were incorporated into the soil 1 week before transplanting. The resykts sgiwed tgat the maximum rate of ammonia volatiliation losses from urea (11.2 kg N rai-1) broadcast into floodwater shortly after transplanting occurred 2-4 days after fertilisation. The cumulative NH3 losses during the 11 days following urea application were 0.74 , 1.30 and 0.90 kg N rai-1 from no residue, burned residue and residue treated plot which corresponded to 7, 12 and 8% aof the appplied N, respectively, At nearly that time N2+N2O emissions were first detected 3 days after urea application. From day 3 to 12 following urea addition, N2+N2O emissions were first detected 3 days after urea application. From day 3 to 12 following urea addition, N2+N2O emission rates averaged 290, 110 and less than 10 ug N m-2hr-1 from no residue burned residue and residue treated plots, respectively or the cumulative percent of N2+N2O emission due to urea addition corresponded to 10, 4.3 and nil. The 15N balance study at grain maturity of the dry seasom rice showed that fertilizer N recovered by the grain, straw and roots did not show significant differences amoung residue treatments. fertilizer N rescovery 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 was probably lost by gasous N emissions which ranged from 27 to 33% of the applied N and was unaffected by residue treatments. Only 4 to 5% of the intial 15n-labeled urea applied to the dry season rice crop was taken up by the succeding rice crop in the wet season to which nbo 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 treatment in either season.