Efficient Management of Nitrogen Fertilizers for Flooded Rice in Relation to Nitrogen Transformations in Flooded Soils

Recent progresses in efficient management of nitrogen fertilizers for flooded rice in relation to nitrogen transformations in flooded soil were reviewed. Considerable progress has been achieved in the investigation on the mechanism of ammonia loss and the factors affecting it. However, little progress has been obtained in the investigations on nitrification- denitrification loss owing to the lack of method for estimating the fluxes of gaseous N products. Thus, so far the management practices developed or under investigation primarily for reducing ammonia loss are feasible or promising, while those for reducing nitrification- denitrification loss seem obscure, except the point deep placement. In addition, it was emphasized that the prediction of soil N supply and the recommendation of the optimal rate of N application based on it are only semi-quantitative. The priorities in research for improving the prediction are indicated.