Five Different Soil Textures Under The Action Of Rainfall-runoff On Slope Erosion Process And Phosphorus Loss Characteristics

Rainfall-runoff is the condition for slope erosion and nutrient loss in farmland,and there is higher nutrient content in sediment than that in topsoil,which is the cause of agricultural non-point source pollution.Existing studies have shown that the key to predicting nutrient loss is the determination of sediment-nutrient enrichment rate.Therefore,this paper takes five soils with different clay contents in Danjiangkou Reservoir area as the research object,and studies the loss of phosphorus under three slope erosion conditions of simulated rainfall,runoff scouring and rainfall-runoff combination and its relationship with rainfall intensity,runoff flow rate,soil texture and initial phosphorus content of soil.The characteristics of soil phosphorus loss and phosphorus enrichment were revealed.The main conclusions were following:(1)With the increase of rainfall intensity or runoff flow rate,the average infiltration rate increases,the initial runoff time shortens,and the soil erosion rate accelerates.The loss of dissolved phosphorus in runoff accounts for 72.1%-86.5% of the total loss of dissolved phosphorus within 10 minutes of runoff.The increase of rainfall intensity or runoff flow rate increases the solid-liquid distribution ratio and reduces the pollution of phosphorus to the environment in a short time.The enrichment rate of phosphorus decreases with the increase of rainfall intensity or runoff flow rate.When the rainfall intensity or runoff flow rate is too large,there is no enrichment effect of sediment on phosphorus.The content of <0.05 mm particle aggregates increases with the increase of rainfall intensity or runoff flow rate,ranging from 62.5% to 86.4%,which is the main body of eroded sediment.The content of phosphorus in <0.05 mm particle aggregates is also the highest,which is the main way for phosphorus loss in eroded sediment.The aggregation effect of <0.05 mm particle aggregates on phosphorus is the strongest,while that of 0.05 mm-0.25 mm particle aggregates on phosphorus is the weakest.(2)The lower the soil clay content,the higher the average infiltration rate,the lower the runoff rate,and the faster the soil erosion rate.The clay content has a significant effect on the contents of dissolved phosphorus and particulate phosphorus:compared with soils with the lowest clay content,soils with the highest clay content have 2.52-3.38 times higher dissolved phosphorus content and 3.40-3.73 times higher particulate phosphorus content.The higher the clay content,the greater the solid-liquid distribution coefficient of phosphorus,and the lower the effectiveness of phosphorus,which reduces environmental pollution.The enrichment rate of phosphorus in sediment increases with the increase of clay content.When the clay content is low,there is no enrichment effect of sediment on phosphorus.Aggregates with a particle size of <0.25 mm are the main components of eroded sediment.The heavier the texture,the lower the content of aggregates with a particle size of 0.05 mm-0.25 mm and the higher the content of aggregates with a particle size of <0.05 mm.The aggregation effect of each particle size aggregate on phosphorus is ranked from large to small as follows: “<0.05mm”,“>1 mm”,“0.50 mm-1 mm”,“0.25 mm-0.5 mm”,“0.05 mm-0.25 mm”.(3)The initial phosphorus content of soil has no significant effect on the erosion process of soil under rainfall and scouring experiments.The contents of dissolved phosphorus and particulate phosphorus increase with the increase of initial phosphorus content,while the solid-liquid distribution coefficient of phosphorus decreases with its increase.The enrichment rate of phosphorus in sediment decreases with the increase of initial phosphorus content.When the initial phosphorus content is too high,there is no enrichment effect of sediment on phosphorus.The higher the initial phosphorus content,the greater the difference in phosphorus content between aggregates at all levels.The content of phosphorus in aggregates with a particle size of <0.05 mm is the highest,while that in aggregates with a particle size of 0.05 mm-0.25 mm is the lowest.