Simulation Of Runoff-erosion And NO₃^--N,PO₄^3--P Loss On Loess Slope Under The Coupling Effects Of Multi-factors

The Loess Plateau is one of the most serious areas of soil erosion in China,and the slope is the main source of sediment into the Yellow River.Although a series of runoff and erosion conservation measures have been carried out for a long time to reduce the amount of sediment into the Yellow River,the problem of runoff-erosion and nutrient loss on the loess slope can not be ignored.Based on this,this paper took the loess slope land as the research object,adopted the indoor artificial rainfall simulation to carry on the continuous rainfall experiment,studied the process and the change rule of runoff,erosion,nitrogen and phosphorus loss on the slope surface under the condition of multiple factors?rain intensity,slope,biochar,vegetation,farming method?,and revealed the influence mechanism of different factors on the runoff,erosion,nitrogen and phosphorus loss on the loess slope.In order to provide a scientific basis for the management of soil and water resources in loess slope land.The main results are as follows:?1?The runoff intensity of each rainfall increased gradually with the rainfall duration and then tended to be stable.When the slope was 20°,the logarithmic function was used to express the optimal value?n?12,R²?0.7,P<0.01?.There was a linear correlation between cumulative runoff and rainfall duration on vegetation slope,and the time when the runoff intensity tended to be stable decreased with the increase of rainfall intensity.When the other influencing factors were same,the larger the slope of vegetation was,the more volatile the runoff generation process was,and the fluctuation of the runoff generation process increased first and then decreased with the increase of biochar content,the largest at 3%,in addition,the fluctuation of the runoff generation on bare slope was greater than that on vegetation slope;when the slope was 10°,the runoff generation capacity can be weakened by transverse ridge,when the slope was 20°,the vegetation can also reduce the runoff,but increased with the increase of rainfall intensity and biochar content.?2?The sediment yield and runoff yield of each rainfall were closely related.There was strong linear correlation between sediment yield rate and runoff yield rate.More than60%of sediment yield rate was determined by runoff yield rate.When the other influencing factors were the same,the sediment yield increased with the increase of rain intensity,slope and biochar content.At the same time,the greater the biochar content and rain intensity was,the greater the rate of increase of total sediment yield was.And when the rain intensity was different,the rate of increase of total sediment yield with slope was also different.When the rain intensity was 60mm/h,the rate of increase of sediment yield with slope from 10°to 15°was greater than that from 15°to 20°When the rain intensity was greater than 90mm/h,the result was opposite to 60mm/h.In addition,the transverse ridge and vegetation can effectively reduce the erosion.The total sediment yield of the transverse ridge slope was 67.3%less than that of the flat cultivation,and the total sediment yield of the bare slope was 42%more than that of the vegetation slope.In addition,the intensity of the sediment yield process was directly proportional to the rainfall intensity,and the sediment yield process was more volatile under the condition of the bare slope than that of the vegetation slope.?3?In the process of NO₃^--N loss,the concentration of NO₃^--N decreased first and then became stable with the rainfall duration,and the loss process showed a power function trend?n?12,R²?0.72,P<0.01?,showed obvious initial scouring effect;The maximum value of NO₃^--N loss concentration was 0.033mg/ml when the rain intensity was 90mm/h and the slope was 15°.When the other conditions were same,the total loss of NO₃^--N increased first and then decreased with the increase of rain intensity and slope,and the loss process was the most volatile when the slope was 15°.The ratio of the maximum value of loss concentration to the minimum value was 3.94;when the rain intensity was 60 and 90mm/h,the loss of NO₃^--N can be reduced by transverse ridge,but when the rain intensity was120mm/h,the results were different;when the rainfall was 60mm/h,the loss of NO₃^--N can be reduced by 3%biochar content,and the loss concentration of NO₃^--N decreased first and then increased with the increase of biochar content;when the rainfall was 90 and120mm/h,the loss concentration of NO₃^--N was positively correlated with biochar content;in addition,the loss process of NO₃^--N on the bare slope was more volatile than that on the vegetation slope,the average loss concentration of NO₃^--N under vegetation slope was 18%less than that of bare slope.?4?In the process of PO₄^3--P loss in each rainfall,the concentration of PO₄^3--P fluctuated little with the duration of rainfall,and there was no obvious regularity.The maximum ratio of the highest loss concentration to the lowest loss concentration of vegetation slope was 1.71,and it was 2.41 under the condition of bare slope,and the loss process under the condition of bare slope was more volatile;When the other influencing factors were same,the loss concentration of PO₄^3--P on vegetation slope was in direct proportion to rainfall intensity and biochar content,When the rainfall intensity increased from 60mm/h to 90mm/h,the loss concentration increased by 18.6%?19.23%,when90mm/h increased to 120mm/h,the loss concentration increased by 4.84%?9.8%,and the total loss of PO₄^3--P increased first and then decreased with the increase of slope;the loss of PO₄^3--P decreased with the increase of transverse ridge and vegetation,and the average loss concentration under vegetation slope was 15%less than that under bare slope,and under the condition of transverse ridge,the loss was 9.2%less than that under the condition of flat cultivation.?5?The influence degree of each factor on runoff,sediment,nitrogen and phosphorus was very different,When the rain intensity was 60?90mm/h,the slope was 10?20°,the content of biochar was 0%?6%,there was vegetation and tillage measure,the main influencing factors of runoff yield were rain intensity,biochar content and vegetation,the decision coefficients were 0.34,0.095 and 0.048 respectively,the main influencing factors of sediment yield were biochar content,rain intensity and tillage measure,the decision coefficients were 0.22,0.097 and 0.038 respectively,the main influencing factors of NO₃^--N loss were rain intensity,runoff yield and sediment yield,the decision coefficients were-0.079,0.217 and 0.155 respectively,and the main influencing factors of PO₄^3--P loss were the content of biochar and the runoff yield,the decision coefficients were 0.195 and0.248 respectively.The indirect effects of various factors were also different,for runoff and sediment,rain intensity,biochar content,vegetation and tillage measure had only direct impact on runoff and sediment,but no indirect impact;for NO₃^--N,the indirect effect of rainfall intensity and sediment yield was negative,while the indirect effect of runoff was positive;for PO₄^3--P the indirect effect of the flow rate through biochar and the flow rate through biochar on the loss of PO₄^3--P was negative.