7. The efficacy and loss of fertilizer N in lowland rice

Nitrogen fertilization is a key input in increasing rice production in East, South, and Southeast Asia. The introduction of high-yielding varieties has greatly increased the prospect of increasing yields, but this goal will not be reached without great increases in the use and efficiency of N on rice. Nitrogen enters a unique environment in flooded soils, in which losses of fertilizer N and mechanisms of losses vary greatly from those in upland situations. Whereas upland crops frequently use 40–60% of the applied N, flooded rice crops typically use only 20–40%. There is a great potential for increasing the efficiency of N uptake on this very responsive crop to help alleviate food deficits in the developing world.This article reviews current use of N fertilizers (particularly urea) on rice, the problems associated with rice fertilization, and recent research results that aid understanding of problems associated with N fertilization of rice and possible avenues to increase the efficiency of N use by rice.