Ammonia volatilization losses and ^(15)N balance from urea applied to rice on a paddy soil

Ammonia volatilization loss and 15N balance were studied in a rice fie ld at three different stages after urea application in Taihu Lake area with a mi crometeorological technique. Factors such as climate and the NH4+-N concentratio n in the field floodwater affecting ammonia loss were also investigated. Results show that the ammonia loss by volatilization accounted for 18.6%—38.7% of urea applied at different stages, the greatest loss took place when urea was applied at the tillering stage, the smallest at the ear bearing stage, and the intermed iate loss at the basal stage. The greatest loss took place within 7 d following the fertilizer application. Ammonia volatilization losses at three fertilization stages were significantly correlated with the ammonium concentration in the fie ld floodwater after the fertilizer was applied. 15N balance experiment indicated that the use efficiency of urea by rice plants ranged between 24.4% and 28.1%. At the early stage of rice growth, the fertilizer nitrogen use efficiency was ra ther low, only about 12%. The total amount of nitrogen lost from different ferti lization stages in the rice field was 44.1%—54.4%, and the ammonia volatilizati on loss was 25.4%—33.3%. Reducing ammonia loss is an important treatment for im proving N use efficiency.