Study Of Hedgerows Types And Distance Between Hedgerows For Non-Point Pollution Control In Purple Soil Aera

For broken geological, ecological fragility, mostly farming-based slope land cultivation in Purple area, soil erosion is more serious, especially after the completion of the Three Gorges Reservoir, the non-point source pollution has become an urgent problem. Hedgerow measures have become an important way of conservation to control non-point source pollution and improve nutrient utilization of agricultural land and other ecological systems. Through plots observation method with a standard laboratory analysis, carried out in the Purple Area 10°,15°sloping land, and in April 2010 planting of Vetiveria zizanioides,Leucaena leucocephala hedgerows in a rainy season, planting around the middle of the slope runoff, sediment, soil nutrient distribution, physical properties, soil erodibility influence on the control slope erosion, agricultural pollution and the derivation of hedgerows with a distance of critical were investigated. The results show that:(1) Effects of hedgerows on intercept runoff:Vetiveria zizanioides hedgerow> Leucaena leucocephala hedgerow. Effects of Vetiveria zizanioides hedgerows on intercept on 10°sloping land better than 15°sloping land. Characteristics of sediment yield curve changes like the characteristics of flow curve and the runoff line. Early in the runoff of each plot, the flow of sediment yield increases with the production increases, with the hedgerow planting time increased, along with the reduction of sediment yield, and changes were gradually stabilized.(2) Under the 10°slope condition, the effects of hedgerows on soil OM, TK, TP, AN, AK characteristics were:Vetiveria zizanioides hedgerow> Leucaena leucocephala hedgerow; and effects on soil TN, AP content were:Leucaena leucocephala hedgerow> Vetiveria zizanioides hedgerow; Under the 15°slope condition, the variation of soil slope is similar to bottom area with the 10°slope, its base value relative to the background is concerned, are to some extent showing a concentration, and on the middle, the top are reduced to some extent, and reduce the rate significantly greater than 10°slope on the corresponding area. Slope factors also have a large degree of influence on soil nutrient characteristics, overall performance:10°＞15°.(3) Slope soil particles smaller soil particles migration from the top to the bottom of the plots, relative to the top of the slope and the slope, increase in its base fine particle content. Soil migration of silt on the slope from the top to the bottom of the plots, changes are in turn reduced the amount of the loss. Planting hedgerows on soil to intercept a significant effect on clay, clay at the hedgerows before the enrichment, soil clay content increased. Effects of Hedgerow on the distribution of clay of the slope:Vetiveria zizanioides hedgerow>Leucaena leucocephala hedgerow. Early in the planting of Vetiveria zizanioides hedgerows, the effect on sand for the 10°slope was significantly greater than 15°slope. Effect of hedgerows on control of soil particles<0.02mm on the loss was fine, in plots bottom, the slope of the location, soil particles before hedgerows<0.02mm mass fraction increased significantly. Vetiveria zizanioides hedgerows to control the slope of soil particles<0.02mm role of soil loss overall performance:10°＞15°. In term of background variation of the amount of negative correlation, Soil moisture content, bulk density compared with the corresponding changes is negatively correlated with soil bulk density, but water content had no significant influence.(4) Planting hedgerows could increase fractal dimension of soil particles of plots, and the variation is consistent with the clay, and effect of hedgerows on the fractal dimension of soil particles was: Vetiveria zizanioides hedgerow>Leucaena leucocephala hedgerow,10°>15°. In addition, the change in fractal dimension of soil sand, silt and clay, respectively the change in a negative correlation, positive correlation, positive correlation coefficients were:-0.840,0.638, 0.899. From the regression equation of view, the fractal dimension of soil particles and the number of general relevance were as follows:clay>sand>silt. After planting hedgerows,10°dispersion coefficient hedgerows plots has reduced, the Leucaena leucocephala hedgerows, Vetiveria zizanioides hedgerows for slope and intercept of clay enrichment significantly, and the influences were:Vetiveria zizanioides hedgerow>Leucaena leucocephala hedgerow,10°>15°.(5) To control soil erosion in the purple area, the key is to control soil clay content. Effect of hedgerow planting on soil erodibility K values in general was as follows:Vetiveria zizanioides hedgerow>Leucaena leucocephala hedgerow,10°>15°. The value of soil erodibility K and soil sand content, microaggregate size<0.002mm dispersion coefficient was significantly positive correlation, correlation coefficients were 0.980,0.836; and with soil silt, clay, organic carbon content and soil fractal dimension were significantly negative correlation, correlation coefficients were:-0.925,-0.833,-0.787,-0.716,-0.807 respectively. Soil sand, silt, clay, organic carbon, organic matter content, aggregation degree and soil erodibility K values most closely related, and soil organic matter and soil clay particles content are effective predictors for soil erodibility on slope in the Three Gorges Reservoir Area.(6) To confirm suitable distance between hedgerows for controlling non-point pollution in purple soil area, its control mechanism for the cropland under different distance between L.leucocephala hedgerows of 10°and 15°gradient cropland was analyzed based on hydro-dynamics. The results indicated that the hedgerows may effectively control soil erosion between hedgerows under the natural precipitation condition if runoff velocity was less than or equal to the start-up velocity of the soil particle(<0.02 mm) while rill erosion was occurring in purple soil area. Through studying the derivation of rill erosion process, it showed that the largest distance between hedgerows for 10°and 15°gradient sloping cropland was 13.73 and 9.00 m respectively. When runoff velocity and start-up velocity of soil particle (<0.02 mm) were in the critical starting condition at the time of rill erosion occurring, the runoff velocity of 10°and 15°gradient slope was 0.183 and 0.190 m/s respectively. It was the main nutrient loss way through soil particle loss on the surface soil, controlling soil particle loss by hedgerow played an important role in the process of non-point pollution control.