Experiment has showed that the effect of CP on the inhibition of nitrification is significant.However,the effect of CP on the decrease of N loss is varied with soil properties.The beneficial role of CP for retaining nitrogn in ammonium form in acid paddy soil may not be attained in calcareous soil,since the volatilization of NH₄-H is usually enhanced in the soil.In the present experiment,the uptake of fertilizer nitrogen by rice plant through the application of CP is increased alightly,but no response is found in crop yield.Field experiments have also proved that the good effect of CP on the rice yield is found on infertile soils on which only a small quantity of nitrogen fertilizer or manures is applied,or even on calcareous soil.