Submitted to: Nutrient Cycling in Agroecosystems
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 10/11/2001
Publication Date: 3/15/2002
Citation: PHONGPAN, A., MOSIER, A.R. EFFECT OF CROP RESIDUE MANAGEMENT ON NITROGEN DYNAMICS AND BALANCE IN A LOWLAND RICE CROPPING SYSTEM. NUTRIENT CYCLING IN AGROECOSYSTEMS. 2002. 66: 122-142. Interpretive Summary: Rice is the most economically important crop of Thailand, one of the world's leading rice exporters. Lowlands in the Central Plain represent a major rice-growing area where approximately 7 million tonnes per year or more than 30% of the total rice production in Thailand is produced. The need for increased rice production in the Central Plain is now widely recognized under intensified cropping systems (i.e. two or three crops per year) with high inputs especially increased tillage, irrigation, and N fertilizer use. High cropping intensity, improper use of crop residue and input use, particularly N fertilizer, has contributed to decreases in soil organic matter (SOM) and soil quality in general. Improved management systems are needed to provide sustainable rice production in Thailand's Central Plain.
Technical Abstract: Two field experiments were conducted in a rice-fallow-rice cropping sequence during consecutive dry and wet seasons of 1997 on a clay soil (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 11d 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. During a 70 d follow period prior to flooding the soil for wet season rice, emissions of N2O measured at weekly intervals from no residue, burned residue and residue treatments ranged from 25 to 128, 19 to 59 and 24 to 75 mg N m-2 h-1 , respectively. The 15N balance study showed that fertilizer N recovered by the rice plant (grain, straw and roots) at maturity of the dry season crop did not show significant differences among residue treatments. Fertilizer N recovery by the grain was low, only 9 to 11% of the N applied. Fifty to 52% 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 gaseous N emissions which 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.