Effects Of Different Fertilization Treatments On Rice Yield And The Risk Of Nitrogen And Phosphorus Losses From Paddy Field

Rice production is the main utilization type of cultivated land in our country. Excessive fertilization leads to the nitrogen and phosphorus losses in its production, which is one of the main source of agricultural non-point pollution. A two-year field experiment was conducted to investigate the effects of six treatments with different fertilizationon on rice yield and loss risks of nitrogen and phosphorus of paddy field. Six treatments are:no fertilization (CK), conventional fertilization(CF),90% of CF (90%CF),80% of CF(80%CF), fertilization with slow release complex fertilizer (CRF), and organic-inorganic fertilization (MF). Major results are as follows:Application of fertilizers sharply increased the concentrations of total nitrogen(TN), ammonium nitrogen(NH4+-N), total phosphorus(TP) and dissoluble phosphorus(DP) to their peaks in surface water after 2 days. Then, the concentrations of TN and NH4+-N rapidly decreased to below 15% of the peak values, and the concentrations of TP and DP rapidly decreased to below 20% of the peak values in 7 days after fertilization. Therefore, it was the critical period to control runoff losses of nitrogen and phosphorus in one week after fertilization. During the period of monitoring, the average TN and TP concentrations in surface water under different fertilization treatments both followed the decreasing order of CF>90%CF>80%CF> MF, CRF>CK. The average TN concentration in surface water of 90%CF,80%CF, CRF and MF was 17.32%,28.44%,44.60% and 34.16% lower than that of CF, respectively(the average of 2 years). The average TP concentration in surface water of 90%CF,80%CF, CRF and MF was 17.61%,33.44%,45.05% and 42.63% lower than that of CF, respectively(the average of 2 years). Reducing fertilization could effectively reduce the average concentrations of nitrogen and phosphorus in surface water. CRF and MF were especially effective on reducing the concentration of nitrogen and phosphorus in surface water. Except for CK, the amount of TN and TP losses from different treatments through runoff were 8.81～15.78 kg·hm-2 and 1.12～2.05 kg·hm-2 in 2015, respectively. Reducing 20% of fertilization could reduce the cumulative runoff losses of TN and TP by 33.52%-44.17% and 24.87%-41.97%, respectively. Inorganic nitrogen was the main forms of nitrogen losses and particulate phosphorus (PP) was the main form of phosphorus in paddy runoff water. The rate of TN and TP losses from different treatments through runoff were 2.58%～4.96% of applied N and 0.52%～1.61% of applied P, respectively.During the period of monitoring, the average TN concentrations in leaching water under different fertilization treatments followed the decreasing order of CF>CF90%>CF80%>CRF, MF>CK. The TN concentration in leaching water of 90%CF,80%CF, CRF and MF was 19.30%,26.58%,51.33% and 51.50% lower than that of CF, respectively(the average of 2 years). Reducing fertilization could effectively reduce the concentration of nitrogen and phosphorus in leaching water. CRF and MF were especially effective on reducing the concentrations of nitrogen and phosphorus in leaching water. NO3--N was the major form of nitrogen leached below 60 cm of paddy field. The average leaching concentrations of TP from different fertilizations were 0.021～0.064 mg·L-1, and these are higher than that of the lowest phosphorus concentration for water eutrophication. The amount of TN and TP losses from different treatments through leaching were 9.29～28.30 kg·hm-2 and 0.18～0.37 kg·hm-2, respectively(the average of 2 years). The rate of TN and TP losses from different treatments through leaching were 3.41%～7.89% of applied N and 0.16%～0.28% of applied P, respectively(the average of 2 years).Except for CK, rice yield and absorption amount of nitrogen and phosphorus with different fertilization treatments were no significant differences. Reducing 20% of N and P fertilization should be feasible in the short term. Utilization rates of nitrogen and phosphorus of different fertilization treatments were 15.86%～22.83% of applied N and 3.82%～7.77% of applied P. Reducing fertilization could increase utilization rates of nitrogen and phosphorus by 4.54%～45.72% and 26.91%～110.76%, respectively. In the estimation of nitrogen balance, ammonia volatilization losses accounted for 3.82%～7.11%, denitrification losses accounted for 15.85%～17.13%, runoff losses accounted for 1.23%～1.91%, leaching losses accounted for 4.83%～7.28%, and crop harvest accounted for 46.66%～55.97% of the total nitrogen input with different treatments, respectively (the average of 2 years). In the estimation of phosphorus balance, runoff losses accounted for 0.75%～1.23%, leaching losses accounted for 0.35%-0.44%, and crop harvest accounted for 31.37%～41.83% of the total phosphorus input with different treatments, respectively(the average of 2 years).In conclusion, it should be feasible to reduce 20% of N and P fertilization in rice production of the study area in a short time which could not only reduce the risk of nitrogen and phosphorus losses from paddy field, but also ensure rice yield and improve utilization of nitrogen and phosphorus.