Abstract:Application of N fertilizer is one of the most important measures that increase crop yield in agriculture. According to statistical data from FAO (1995), the contribution of N fertilizer application to the newly increased yield reaches 50% since 1960‘s in the whole world. However, misuse of N fertilizer (particularly overuse) will also cause the decline of economic effects and related environmental problems like N gas emission to atmosphere and NO_3-N leaching to groundwater. Thus it is of course significan...