| Loess Slope water and soil nutrient loss not only led to deterioration in the quality of land, but also caused water pollution. Based on the artificial rain method in the laboratory, the movement rule of water and soil nutrient in sandy loess was researched. It had an important theoretical value and production significance on the mechanism of degradation of soil quality, the control of agricultural non-point source pollution, increasing productivity and the establishment of dryland sustainable development of dryland agriculture. The main research conclusions as followed:1. The effect of initial water content on soil erosion and nutrient loss had a turning point in the relative water content between 49.4% and 76.9%.Both runoff and soil erosion increased as soil water content increased, and they had relation of exponential function; the initial exponential model could be better reflect the relationship between nutrient runoff and the loss of soil water content;2. Sandy loess using PAM when the amount of PAM was≥0.5 g.m-2 showed infiltration reduction in the volume and increasing of runoff. PAM application can be effective in reducing soil erosion, and erosion with the increased use of PAM reduced. Sandy loess using PAM reduced the soil moisture infiltration, but the indirect effects of the reduction in soil moisture infiltration weakened the deep nitrate leaching, and had little impact on soil adsorption of phosphorus and potassium. Although the increase in runoff caused the total amount of nitrate, soluble Water-soluble potassium and phosphorus increased , the analyses showed that nutrients through runoff and Sediment loss were little; nitrate decreased mainly through nitrate leaching losses, phosphorus and potassium mobility were weak and fixed by soil, so not losses too much . Considering From an economic point of view and the erosion of the law, the level of PAM use was between 1 and 3 g.m-2;3. Straw mulch protected the ground from direct combat raindrops, avoided surface crust formation, and got more rain in the rainy season. The results showed that: straw mulch delayed runoff time, significantly reduced runoff, increased filtration and effectively controlled soil erosion, 250,500,1000,1500 g.m-2 deal with straw mulch comparing with the control reduced erosion of 94.8%, 97.2%, 98.6% and 78.6% and runoff of 20.2%, 39%, 29.5% and 41.5% respectively. Comparing with a single application of PAM, Using straw mulch and PAM was reduced of 98% erosion. In different rainfall intensity of the same straw mulch, storm water runoff time was ahead as the rainfall intensity increased, and the total runoff and erosion increases with the increase in rainfall intensity.Both Straw mulch and straw mulch with PAM reduced the loss of nitrate runoff, at the same time increased the deep nitrate leaching in the soil, reduced the runoff of water-soluble phosphorus and sediment loss of the available phosphorus, and increased the runoff of water-soluble potassium loss and potassium leaching. In different rainfall intensity of the same straw mulch, nitrate runoff, the water-soluble and water-soluble phosphorus loss of potassium increased as the increase in rainfall intensity. Considering from the amount of soil erosion, nutrient runoff and sediment loss, wheat straw mulch in the 250 to 1000 g.m-2 was suitable;4. On Loess Plateau, we toke the measures of which sandy loess and straw were mixed to advance runoff duration. When straw mixture excess 500 g.m-2, infiltration reduced and runoff increased, which cause soil erosion seriously. After mixing straw, runoff and nutrients in sediment increased, and with the mixing straw increased, runoff and nutrients in sediment increased simultaneously. Straw mixing weakened the nitrate nitrogen leaching of the deep soil, but affected less on the available phosphorus and potassium content of soil profile.5. Soil erosion had slope limits, when slope≥15°, erosion began increasing and achieved the maximum at 20°. After that, erosion decreased with the slope increased. Slope affected on nutrient loss of runoff through runoff plays a dominant role.6. The affection of which vegetation coverage effected on the runoff and sand of the slope had vegetation coverage limitation. The amount of nutrient loss decreased with the vegetation cover increased. To some degree, how much the nutrient loss was determined by the runoff amount.
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