The Experimental Study On Sloping Farmland Soil Erosion And Nutrient Loss Processes In The Black Soil Region Of Northeast Plain

Northeast black soil plain is one of the three black soil regions in the world. Due to natural factors and human unreasonable production activities, soil erosion is a serious problem in this area, which has affected food security in our country. The objective of this study was to investigate the effects of rainfall intensities, rainfall patterns, mulch cover rate on sloping farmland black soil erosion and nutrient losses process under simulated rainfall experiments. The conclusions were as follows:1. With the rainfall intensity increase in rainfall event, the total runoff was increased, soil loss under 60 mm/h was 16.5 times higher than it under 30 mm/h, but soil loss decreased by 24% under 90 mm/h compared with it under 60 mm/h. The concentration of NO₃-N, NH₄-N and PO₄-P in runoff was reduced with rainfall duration prolonged under different rainfall intensities, and the concentration of them had good power function relation with rainfall duration. Nutrient accompanied by runoff was primary way for nutrient losses of sloping farmland in black soil region.2. The research analyzed effects of different rainfall patterns on sloping farmland soil erosion and nutrient loss process. The trends of flow rate and sediment yield rate were consistent with rainfall intensity in rainfall patterns, and change of rainfall had a strong influence on flow rate and sediment yield rate. Delayed type had more runoff than weaken type, and central-peaked type had less runoff than weaken type, but the amount of soil loss in central-peaked type was larger than the other two types. The contribution of rainfall intensity on runoff and soil loss was different under different rainfall patterns. Cumulative runoff and soil loss increased with rainfall duration continued, however, the growth rate of different period was various.3. The Nutrient losses from sloping farmland increased with rainfall intensity increase under the same rainfall pattern and underlying surface, and nutrient losses had positive correlation with rainfall intensity in same period under various rainfall patterns. Nutrients accompanied by runoff played an important part in nutrients losses, which account for 69.9-76.38% in total amount nutrients losses, while the contribution of sediment ranged 23.62-30.1%. Compared with other two rainfall patterns, central-peaked type had large amount of nutrient loss, which was 3.16 and 3.27 times higher than delayed type and weaken type, that means nutrient loss would sharply increased if rainfall after fertilizer input for a short time. Contents of NO₃-N, NH₄-N and PO₄-P in soil profile were smaller after rainfall than those before rainfall, because some of them lost from runoff and sediment. Contents of NH₄-N and PO₄-P in soil profile decreased as soil depth increase, while the content of NO₃-N increase at first and then decrease later with soil depth increase.4. Quantified effects of mulch cover on sloping farmland soil erosion and nutrient loss in the black soil region. The results showed that compared with the bare land when corn mulch cover was 2 kg·m^-2, runoff decreased by 87% and the soil loss reduced by 99.86%, respectively. For 4 kg·m^-2 of corn mulch cover, runoff did not occur. Under the 2 kg·m^-2 mulch cover treatment, NO₃-N and PO₄-P concentrations in runoff were 5.52 and 4.25 times higher than from the bare land, but total losses of NO₃-N and PO₄-P in runoff from mulch cover treatment were similar to bare land. NO₃-N and PO₄-P in eroded sediment from low mulch cover were 4.38 and 2.93 times greater than from the bare land; but total losses of NO₃-N and PO₄-P in eroded sediment from mulch cover treatment reduced by 99.3% and 99.6%, respectively.