Effects Of Phosphorus Loss From The Phosphorus Application On The Rice-wheat And The Threshold Of Phosphorus Input

As the primary industry of our country,agriculture not only bears the heavy responsibility of food production safety,but also undertakes the arduous mission of ecological environment security.In recent years,due to the excessive input of chemical fertilizers,the phosphorus content of farmland soil in Chaohu basin is increasing,and the risk of agricultural non-point source pollution is increasing.Phosphorus is the main influencing factor of eutrophication of water body.It is of great significance to reduce the phosphorus loss and ensure the environmental safety.In this study,under field conditions of Chaohu basin under different P fertilizer application,yield characteristics change and its track and field water,wheat and rice field surface water and leaching water and soil phosphorus,phosphorus content of Chaohu basin in order to get under the rice wheat rotation effect on phosphorus loss in the farmland and farmland fertilizer input threshold.The results show that:（1）After the application of P fertilizer,the total phosphorus and soluble total phosphorus increased with the increase of phosphorus application rate,but the overall concentration showed a sharp downward trend with the passage of time.On the first day after the application of phosphate fertilizer,blank treatment（T1）and optimization P（T2）,optimized P200%treatment（T3）,optimized P 400%（T4）surface water soluble phosphorus,total phosphorus concentration peak,respectively:0.798 mg/L,1.574 mg/L,2.755 mg/L and 7.133mg/L.The maximum concentration of soluble total phosphorus in surface water of T1-T4treatments was 0.327 mg/L,0.667 mg/L,1.542 mg/L,3.933 mg/L,respectively.After one week,the concentration of total phosphorus and soluble total phosphorus in the surface water of each treatment tended to be stable,and the concentration was lower.Therefore,one week after the application of phosphate fertilizer in the paddy field,it is the peak period of phosphorus loss,and it is also the key period to control the loss of phosphorus in the soil.（2）The runoff coefficient of wheat season and rice season were respectively 24.12%and28.65%,and the annual runoff coefficient was about 26.39%.The runoff coefficient of rice season was higher than that of wheat season,but the gap was smaller.（3）There was a positive correlation between total phosphorus runoff loss and P application rate,and there was significant difference in P application.From the whole monitoring cycle,the total phosphorus loss in the wheat season was 0.201-0.829 kg.hm^-2,the total phosphorus loss coefficient was 0.112%-0.174%.The total phosphorus loss in the rice season was0.294-1.148 kg.hm^-2,and the total phosphorus loss coefficient was 0.012%-0.316%.The total phosphorus loss in rice season was greater than that in wheat season,accounting for 52.9%of total phosphorus loss.（4）The concentration of total phosphorus and soluble total phosphorus showed a decreasing trend with the increase of soil depth.The concentration of total phosphorus and soluble total phosphorus increased with the increase of P application rate.20cm,40cm,60cm,90cm soil layers of the total concentration of T1-T4 treatments were:0.090-1.381 mg/L,0.067-1.263 mg/L,0.051-1.020 mg/L,0.019-0.516 mg/L.The range of soluble total phosphorus concentration was 0.029-0.578 mg/L,0.025-0.370 mg/L,0.018-0.312 mg/L,0.006-0.225 mg/L,respectively.（5）Compared with no P fertilizer treatment,the yield of all P treatments increased,but there was no significant difference among the treatments.The highest yield of T2 treatment was 3578.89 kg.hm^-22 in wheat season(P:90 kg.hm^-2).The highest yield of T3 treatment was8932.41 kg.hm^-22 in rice season(P:180 kg.hm^-2).（6）The input of phosphorus could significantly increase the phosphorus uptake of crops,and the phosphorus uptake of crop straw and grain showed an increasing trend with the increase of P application rate.The total phosphorus uptake of rice was higher than that of total phosphorus uptake.The phosphorus uptake of wheat and rice grain was greater than that of straw,and the total nutrient uptake of T1-T4 treatments was 11.99-32.35 kg.hm^-2.The range of total phosphorus uptake by T1-T4 treatments was 46.33-80.29 kg.hm^-2.（7）The utilization rate of phosphorus fertilizer with the increase of P fertilizer is showing an overall decreasing trend,wheat under different P fertilizer utilization rate for the5.66%-8.74%season,the utilization rate of phosphate fertilizer in rice season 12.58%-18.40%.The utilization rate of phosphate fertilizer in rice season was higher than that in wheat season.（8）The Olsen-P content in the wheat season was higher than that in the rice season with different P treatments in Olsen-P.The Olsen-P content of farmland soil decreased with the increase of phosphorus application rate under different treatments of rice wheat rotation.The range of Olsen-P content of wheat in different treatments was 11.13-29.92 mg.kg^-1.The range of Olsen-P content in the soil of paddy field in T1-T4 treatments was 8.87-21.73 mg.kg^-1.（9）Based on the amount of P fertilizer,yield,soil Olsen-P,fertilizer utilization rate,it is concluded that the optimal phosphorus fertilizer input range is 87.49-185.38 kg.hm^-2.Soil Olsen-P is 15.94-20.99 mg/kg,total phosphorus loss is 0.35-0.53kg.hm^-2.The optimal phosphorus fertilizer input range of rice season is 74.97-153.78 kg.hm^-2.Soil Olsen-P is12.56-16.30 mg/kg,total phosphorus loss is 1.24-1.68 kg.hm^-2.The results of this study can provide the basis for the development of the scientific application of phosphate fertilizer,and provide guidance for controlling agricultural non-point source pollution and reducing environmental risk.