| With the rapid development of social economy,water shortage caused by water quality and resource shortage is becoming more and more serious.After the point source pollution has been controlled and treated,water quality water shortage is mainly related to the eutrophication of water body caused by farmland non-point source pollution.Because of unreasonable fertilization,N and P in farmland are lost into the surrounding water body under the effect of rainwater runoff.Besides unreasonable fertilization,N and P loss in farmland is closely related to plant coverage and rainfall intensity.It is very important to understand the mechanism of water and fertilizer loss for controlling non-point source pollution.Therefore,taking rape as a typical dry crop,this paper studied the characteristics of nitrogen and phosphorus loss with runoff under different rainfall intensity and vegetation coverage in different growth periods.Rainfall is abundant in southern China.Besides fertilization,the formation of non-point source is closely related to rainfall intensity,vegetation coverage and other factors affecting runoff yield.In this paper,five plant coverage(designed as 0,20%,50%,80%and 100%in design,and measured as 0,20%,49%,79%and 100%in actual test)in different growth stages of rape were used for plot test,and three constant rainfall intensities(4mm/h,7mm/h and 13mm/h)were simulated to explore the process characteristics of agricultural runoff and the law of N and P loss with runoff in rape field,so as to provide reference for future farmland drainage and water control The results provide the basis for the control of fertilizer loss and water eutrophication.The main research contents and achievements are as follows.(1)Under different rainfall intensities,the runoff process was significantly correlated with different plant coverage.The smaller the rainfall intensity is,the longer the initial runoff generation time is.The relationship between rainfall intensity and initial runoff generation time is an exponential function.When the vegetation coverage is more than 50%,the impact on the initial runoff generation time is the most significant.The runoff in the early 20 minutes increases first and then decreases with the increase of vegetation coverage.According to this feature,we can use the plant coverage as a parameter to modify the farmland runoff model,so as to better reflect the change of Farmland Runoff under different crop coverage.(2)Under three different rainfall intensities,the effects of different vegetation coverage on N loss were different.With the increase of vegetation coverage,the concentrations of TN,NO3--Nand NH4+-Nin the drainage increased gradually.The average concentration of TN loss was the fastest in the stage of 22%to 49%vegetation coverage,and tended to be stable in the two stages of 0%to 22%vegetation coverage and 79%to 100%vegetation coverage.Meanwhile,the average concentration of NO3--N loss also increased with the increase of vegetation coverage,and increased in the stage of 49%to 79%The average concentration of NH4+-N also increased with the increase of vegetation coverage.Contrary to the increase of TN average concentration,the rate of NH4+-N loss was the slowest in the period of 22%to 49%vegetation coverage.This shows that the increase of vegetation coverage can not reduce the concentration of N in soil drainage in this area,but can reduce the total drainage through the impact of runoff generation,thus reducing the total amount of N loss;at the same time,it is found that the lower the rainfall intensity is,the greater the average concentration of N loss is.(3)Under three different rainfall intensities,different vegetation coverage had significant effect on reducing P loss.With the increase of vegetation coverage,although the average concentration of DP increased,the average concentration of TP decreased,and the decrease was greater than the increase.Therefore,different vegetation coverage had a significant role in reducing the loss of farmland P.At the stage of 79%～100%vegetation coverage,the increase of vegetation coverage has the most significant effect on reducing the loss of TP,so the increase of vegetation coverage can effectively reduce the loss of TP in soil drainage in this area.The average concentration of DP increased fastest in the stage of vegetation coverage from 79%to 100%.At the same time,it is found that the lower the rainfall intensity is,the higher the average loss concentration of P is.The results show that the systematic error of the test is small and the sampling data are relatively stable.The test results can provide a scientific basis for the control of farmland non-point pollution sources in the future. |
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