| Purple soil is widely distributed in Three Gorges reservoir area with high erodibility to cause soil erosion. Soil erosion on slope farmland converts great contribution on agricultural non-point source pollution. How to control planting non-point source pollution is urgent problem. Monitoring soil loss of different fertilization levels is basis for the control of non-point source pollution. Based on different fertilization level, this experiment set control (K), normal (C), optimized (F), increased (I), and conservation tillage (P), five different fertilization treatment test plots with three repeated. Studding on the soil physical and chemical properties and the nutrient content in plants was based on plots field experiment and samples test. To know how the fertilization affect on plant nutrient accumulation and soil nutrient loss, the author plotted the curve of correlation between fertilization and plant nutrient accumulation, and the curve of correlation between fertilization and soil nutrient loss. To get soil erodibility and the amount of soil nutrient elements loss is the foundation to know how much fertilization needed and control soil erosion in Three Gorges reservoir area. The results show that:(1) Soil mechanical composition changed in test plots after maize harvested. Soil clay content were raised in plot K and P; but dropped in plot C, F and I. Soil sand content were increased in plot C, F and I. Soil texture changed because of the change of soil mechanical composition, silt soil changed into silt loam soil in plot C, and silt loam soil changed into silt clay soil in plot P, after harvested. Compared with conventional tillage, conversation tillage could prevent the soil particles move and decrease soil loss. There was a significant positive correlation between soil clay and soil fractal dimension; and negative correlation between silt, sand and soil fractal dimension. Soil mechanical composition took a decisive effect on soil fractal dimension. Soil erodibility K value raised at every sampling point in each test plot after harvested. There was a significant positive correlation between silt with 0.05-0.01mm particle diameter and soil erodibility; and a significant negative correlation between sand with 0.25-0.05mm particle diameter and soil erodibility. Took paried T-test with the soil erodibility K value which estimated by EPIC before maize planted and after maize harvested, the result showed that the soil erodibility had non-significant change, and that told the soil physical and chemical properties change do little about soil erodibility K value.(2) Soil chemical properties changed during the maize planting season, soil chemical properties showed obvious differences at the bottom in each test plot. There was little differences of soil chemical properties in plot K. There showed highly obvious differences in plot I, and low differences in plot I, among fertilization test plot. After maize harvested, generally speaking, soil organic matter increased; soil total nitrogen, ammonium nitrogen and nitrate nitrogen contents increased obviously on the top and the bottom of the test plot, but decreased at the middle of the slope; soil total phosphorus and available phosphorus had the same trend and increased in each plot; soil total potassium decreased, but available potassium increased in each plots.(3) Plant nutrient absorptions showed differences at various slope, plants absorbed the similar amount of nitrogen and potassium at the top of each test plot, but great difference of phosphorus absorption. Plant nutrient absorptions of nitrogen, potassium, and phosphorus all decreased in the middle of each plot. Plant nutrient absorptions became the similar at the bottom of each plot. The plant nutrient absorptions had the same trends with the change of soil chemical properties. It would be easy to plant to absorb the soil nitrogen under the situation of conservation tillage or organic nitrogen application. The plant got high nitrogen content at the middle of the plot C in which organic nitrogen fertilization applied, and the plant also got high nitrogen content at the middle and the bottom of the plot P in which conversation tillage used. The plant had more nutrient absorptions in the test plot which cultivated in conservation tillage under the same fertilization level.(4) Considering the soil nutrient loss by soil nutrient element input and output, the author built the equation:L=Ta-Tb+I- Y; by obtained the soil chemical properties of the maize planted before and harvested after, the amount of plant nutrient absorptions and the fertilization applications in each plot. There was a positive correlation between fertilization and the plant nitrogen accumulation, and the same with plant potassium accumulation, by built the relationship of fertilization and the plant nutrient accumulation. In order to get the relationship of fertilization and the amount of soil nutrient loss, the author built the curves of the fertilization and the amount of nutrient loss. The curves showed that:There was a positive correlation between fertilization and the amount of potassium loss. The relationship of fertilization and the amount of nitrogen loss showed as a inverted U shaped curve, the maximum appeared in the range of optimized fertilization and increased fertilization. The relationship of fertilization and the amount of phosphorus loss showed as a U shaped curve, the minimum appeared in the range of non-fertilization and optimized fertilization. The amount of nutrient loss was controlled by used conversation tillage under the same fertilization level. The coverage also could affect the loss, it showed that the amount of soil phosphorus and potassium loss were lower in good coverage test plot. |
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