Characteristics Of Nitrogen Loss In Loess Slopes Simulated By Different Measures Under Rainstorm

Controlling soil nutrient loss on slopes is the key to preventing soil erosion and non-point source pollution in the Loess Plateau.In this paper,an indoor artificial simulated rainfall test is adopted,and 3 rain intensities（60,90,120 mm/h）,3 slopes（10°,15°,20°）,and 3 types of biochar content（BC,0%,3%,6%）,2 farming methods（flat cropping P,horizontal ridge H）and 2 types of underlying surface（bare land L,vegetation Z）,a total of bare land:LP0（flat cropping）,LH0（horizontal ridge）,LP3（3%BC）,LH3（horizontal ridge+3%BC）,LP6（6%BC）,LH6（horizontal ridge+6%BC）,vegetation:ZP0（flat cropping）,ZH0（horizontal ridge）,ZP3（3%）BC),ZH3（horizontal ridge+3%BC）,ZP6（6%BC）,ZH6（horizontal ridge+6%BC）and other 12 treatments,to study the total nitrogen（TN）and total solubility of slope runoff under simulated heavy rain The loss characteristics of nitrogen（DN）,adsorptive total nitrogen（PN）and ammonium nitrogen（NH₄⁺-N）,analyze the effects of different treatments on slope erosion and nitrogen loss,and quantify the relationship between nitrogen loss forms and proportions under different treatments,with a view to Provide a scientific basis for the treatment of agricultural non-point source pollution on slope farmland in the Loess Plateau.The main conclusions are as follows:（1）Under the conditions of 90 mm/h rain intensity and different slopes,there are significant differences in the nitrogen loss process between the bare slope and the vegetation slope with different measures.The TN and DN loss rates on the slope are basically the same as the rainfall duration,and both decrease rapidly 20 minutes before runoff,and then stabilize.The PN loss rate on the slope has a significant difference with the rainfall duration.The PN loss rate under ZH0,ZH3 and LH0 fluctuates steadily with the rainfall duration.LH3 first rises and then stabilizes,while ZH6 shows a downward trend;different measures The NH4+-N and sediment loss rates are basically the same with the rainfall duration,and both increase 20 min before runoff,and then stabilize.The nitrogen loss of different forms under LH0,ZH0 and ZH3 are all stable in the lower area,indicating that there is a single horizontal ridge（LH0）,or a combination of vegetation and horizontal ridge（ZH0）,or a combination of vegetation,horizontal ridge and 3%biochar（ZH3）.Can effectively alleviate soil erosion and nitrogen loss on slopes.（2）Slope and rain intensity:Under different slope and rain intensity conditions,there are differences in the cumulative nitrogen（TN,DN,PN）loss and the trend of total sediment yield on bare slopes and vegetation slopes.Under the condition of rain intensity of 60 mm/h,the cumulative TN and PN losses on bare slopes and vegetation slopes show a trend of first decreasing and then increasing with the increase of slope.The cumulative DN losses increase with the increase of slope;90 mm/h rain under strong conditions,the amount of TN and DN loss on bare slopes and vegetation slopes increase first and then decrease with the increase of slope.PN loss on bare slopes increased first and then decrease with the increase of slope,while PN loss on vegetation slopes increase with the increase of slope.The slope increasing showes a trend of first increasing and then stabilizing;under the conditions of 60mm/h and 90 mm/h rain intensity,the total sediment yield of the bare slope and the vegetation slope has no obvious law with the slope;in summary,it can be seen that the rainfall at 60 mm/h Under strong conditions,there may be critical slope values of TN and PN on bare slopes near 15°,and there may be critical slope values of nitrogen on bare land and vegetation slopes near 20°under 90 mm/h rain intensity.（3）Vegetation:Vegetation measures under different slope and rain intensity conditions show obvious effects of reducing sediment and nitrogen.In general,the cumulative nitrogen loss and total sediment yield on vegetation slopes are smaller than those of bare slopes.The range of PN/TN ratio of vegetation slopes at different slopes is as follows:9.64%～64.50%,27.69%～51.33%,and 17.88%～44.10%,which are smaller than the PN/TN range of bare slopes at the same slope of 42.62%～79.04%,31.46%～83.99%and 51.71%～78.10%,the PN/TN ratio of vegetation slopes under different rain intensities ranges from29.64%～38.82%,13.50%～34.73%,33.27%～56.86%,which are smaller than bare slopes under the same rain intensity The surface PN/TN ranges are 30.60%～64.01%,17.34%～63.02%,42.62%～79.04%,indicating that vegetation measures under different slopes and rain intensities can effectively reduce the PN/TN ratio under both gentle and steep slopes.（4）Biochar:Nitrogen and total sediment yield on bare slopes and vegetation slopes under different slopes and rain intensities increase with the increase of biochar.Under the bare slope,6%BC≈3%BC>0%BC,indicating that the application of biochar within the scope of this experiment will aggravate nitrogen loss and soil erosion on the bare slope slope;under the vegetation slope,6%BC>3%BC≈0%BC,indicating that a single vegetation measure or vegetation+3%BC has a good effect of reducing sediment and nitrogen,but when vegetation is combined with 6%BC,nitrogen and sediment loss on the slope increases sharply.It is inferred that 3%BC and 6%BC on bare slope slopes belong to excess biochar,while 3～6%BC belongs to excess biochar.Therefore,it is not recommended to apply biochar on bare slopes in actual agricultural production,but it can be applied on vegetation slopes.Biochar in the range of 0%～3%（ZP0～ZP3）is expected to achieve the effect of further sand reduction and nitrogen fixation.（5）Horizontal ridges:The setting of horizontal ridges on the bare slope under different slopes and rain intensities has different changes in reducing slope erosion and nitrogen loss,but the setting of horizontal ridges on vegetation slopes has a different effect on reducing slope soil erosion and nitrogen loss.The law of change is consistent.The reduction effect of horizontal ridges on bare slopes on nitrogen and sediment decreases with the increase of slope and rain intensity,and it is easy to fail under extremely heavy rain and steep conditions;while horizontal ridges on vegetation slopes reduce nitrogen and sediment The effect is enhanced with the increase of slope and rain intensity.It can still play a significant role in reducing sediment and nitrogen under conditions of extreme heavy rain and steep slope.The nitrogen reduction rate and sediment reduction rate are optimally above 55%,indicating that vegetation+horizontal Ridges can more effectively control nitrogen loss from slopes.Therefore,in actual agricultural production,it is recommended to arrange vegetation and horizontal ridge measures（ZH0）to reduce the risk of nitrogen and sediment loss caused by the increase of rain intensity and slope.（6）Dissolved and adsorbed nitrogen:Under different slope and rain intensity conditions,the PN/TN ratio of bare slopes and vegetation slopes varies greatly under different measures.Under different slopes,the nitrogen loss from the naked slope is mainly PN loss,and the vegetation slope is mainly DN loss,and the increase of the slope will significantly increase the ratio of PN/TN of the naked slope;under different rainfall intensities,the nitrogen loss from the naked slope is 60%.Under～90 mm/h,DN loss is the main cause,and under 120mm/h,PN loss is the main cause.Overall,the PN/TN ratio increases with the increase of rain intensity;while the vegetation slope is subject to 0%and 3%BC is mainly DN loss under different rain intensities,and 6%BC is mainly PN.In addition,the effect of horizontal ridges on reducing the PN/TN ratio of different biochar bare slopes is ineffective,and horizontal ridges can effectively reduce the PN/TN ratio of vegetation slopes without or with 3%BC.Therefore,in actual agricultural production,it is recommended to deploy 0%～3%biochar,horizontal ridges and vegetation measures.It is not recommended to install biochar,horizontal ridges or a combination of both on the bare slope.