Nitrogen losses from fertilizers applied to maize, wheat and rice in the North China Plain

Ammonia volatilization, denitrification loss and total nitrogen (N) loss (unaccounted-for N) have been investigated from N fertilizer applied to a calcareous sandy loam fluvo-aquic soil at Fengqiu in the North China Plain. Ammonia volatilization was measured by the micrometeorological mass balance method, denitrification by the acetylene inhibition - soil core incubation technique, and total N loss by N-15-balance technique. Ammonia loss was an important pathway of N loss from N fertilizer applied to rice (30-39% of the applied N) and maize (11-48%), but less so for wheat (1-20%). The amounts of unaccounted- for fertilizer N were in the order of rice > maize > wheat. Deep placement greatly reduced ammonia volatilization and total N loss. Temperature, wind speed, and solar radiation (particular for rice), and source of N fertilizer also affect extent and pattern of ammonia loss. Denitrification (its major gas products are N-2 and N2O) usually was not a significant pathway of N loss from N fertilizer applied to maize and wheat. The amount of N2O emission (N2O is an intermediate product from both nitrification and denitrification) was comparable to denitrification loss for maize and wheat, and it was not significant in the economy of fertilizer N in agronomical terms, but it is of great concern for the environment.