Zhu, Z.L., Cai, G.X., Simpson, J.R. et al. Fertilizer Research (1988) 18: 101. doi:10.1007/BF01049507
Losses of nitrogen were investigated after applications of ammonium bicarbonate and urea to flooded rice at transplanting. Ammonia (NH3) volatilization was determined by direct micrometeorological methods, and total loss of fertilizer nitrogen (N) was measured by15N balance. All the loss appeared to be in gaseous forms, since there was no evidence of leaching and runoff was prevented. The difference between N loss and NH3 loss was thus assumed to be denitrification loss.
Both NH3 volatilization and denitrification losses were large, being 39% and 33%, respectively, of the ammonium bicarbonate N, and 30% and 33%, respectively, of the urea N applied by farmers' methods.
Ammonia fluxes from the field fertilized with ammonium bicarbonate were very high for two days, and then declined rapidly as the NH3 source in the floodwater diminished. Moderate fluxes from the field fertilized with urea continued over 6 days, but calculations showed that NH3 transfer from floodwater to atmosphere was retarded during the middle period of the experiment, particularly on day 2 when a thick algal scum appeared on the water surface. The results indicate that this algal mass obstructed the transport of NH3 across the water-air interface until the scum was dispersed by wind action. Nevertheless, the prolonged NH3 losses on the urea treatment were due primarily to high floodwater pH values promoted by the strong algal growth during the daylight hours.
Nitrogen-15 balance studies showed that incorporation of fertilizer into drained soil substantially increased recoveries of fertilizer N in rice plants and soil compared with incorporation of fertilizer in the presence of standing floodwater. Ammonia loss measurements on these treatments when urea was applied suggested that the improvement in fertilizer N efficiency was due mainly to reductions in NH3 loss.