Effects Of Fertilization Reduction On Rice Yield And Nitrogen And Phosphorus Losses From Paddy Field

Paddy field is the main utilization type of cultivated land in China.Excessive fertilization leads to the losses of nitrogen and phosphorus,which is one of the main source of agricultural non-point source pollution.To reduce the nitrogen and phosphorus losses in paddy,and meanwhile guarantee the production of rice,the dynamic characteristics of N and P in surface and leaching water and their potential environmental impact were studied by field experiments with different N and P application.The main results as follows:（1）The application of chemical fertilizer can obviously improve the concentration of NH₄⁺-N and NO₃^--N in surface water in paddy field.The concentration of NH₄⁺-N reached to maximum in 2 days and then decreased rapidly in 5 days after the application of basal fertilizer..Straw returning can reduce the content of nitrogen.The application of fertilizer can improve the concentration of P。Besides,improving the usage of N also can increase the content of P in surface water.The level of phosphate fertilizer has influence on the distribution of P.The proportion of MRP/TP is increasing,and the proportion of PP/TP is decreasing with the increase of phosphate fertilizer.（2）Fertilizer application increased the leaching risk of ammonium nitrogen and nitrate nitrogen.The concentration of NH₄⁺-N and NO₃^--N increased with the improvement of chemical fertilizer input.Phosphate fertilizer reduction can effectively reduce the concentration of phosphorus in the leakage solution.With the increase of soil depth,The concentration of TP decreased gradually.In the depth of 20cm soil layer,TP concentration reached the peak at the 2nd day after the application of phosphate fertilizer,while in 40cm and 60cm reaching the peak value on the 5th day.Straw returning could reduce TP content of leaching solution,but the difference between treatments was not significant.The TDP also showed the same trend in each soil layer leakage solution.In 0-20cm soil layer,the MRP/TP of different treatments increased with the increase of phosphate fertilizer,and when P fertilizer level reached 90 kg﹒hm^-2,the ratio of MRP to TP increased significantly,while PP/TP showed a trend of decrease.DOP/TP did not show obvious regularity.There was no obvious regular change of MRP/TP,DOP/TP and PP/TP in the leakage solution of 40cm and60cm soil layers under different P levels..（3）The rice production was not significantly reduced with 162 N kg﹒hm^-2 and 68 P kg﹒hm^-2 on the whole,the concentration of nitrogen and phosphorus in grain was higher than that of glume and stem leaf.Besides,the nitrogen concentration of rice was higher than that of phosphorus.Most of the N and P absorbed in the growth period were accumulated into the grain,and straw returning can promote the transfer of N to the grain.The agronomic efficiency was reduced with the improvement of N and P levels.Likewise,the efficiency of P also shows a trend to decrease with the increase of nitrogen and phosphorus fertilizer.When the nitrogen fertilizer was reduced to 162 kg﹒hm^-2 and phosphate fertilizer was reduced to 68kg﹒hm^-2,the rice yield could maintain the original level while reducing the nitrogen and phosphorus runoff and leakage risk in the rice field.