The Impact Of Soil Water Conditions To Erodibility And Slope Erosion Of Ultisols In Southen Hubei Province

Water plays an important role in the process of soil erosion. Soil erosion process is usually attributed to the interaction of water erosion and soil erodibility, erosivity of water and erodibility of soil is the foundation in understanding and predicting soil erosion practice. Soil water conditions have a variety of patterns, including soil moisture, water movement, soil water hydraulic gradient etc. A large number of researches or studies have shown that soil water conditions do affect soil erosion process, but most soil erosion prediction model does not adjust the relevant parameters. Therefore, further study which focus on the effect of soil water conditions on soil erosion is especially necessary, in order to improve the existing soil erosion models.In this study, the red soils derived from three kind of parent material(quaternary,granite, argillaceous shale) in southeastern Hubei was under research, in order to consider the impact of soil water conditions on rill erosion process and interrill erosion process respectively based on the theory of WEPP model. The main conclusions obtained are as follows:(1) Soil water conditions do has influence when it comes to rill erodibility,average rill erodibility values() of air dry was significantly higher than that of saturated and drainage, and then the difference between the last two was not that significant. In the process of air dry condition to drainage condition and then to the saturated condition, that simulated natural side slope that soils turn form dry to wet then appear seepage process. When antecedent soil moisture is low, the influence of very fine sand content, clay content and soil water content to rill erosion processes can be significant, with the constantly water infiltration in soils, the soil moisture’s impact weakening to insignificant rapidly; Although the influence of clay content at the beginning stage is lower than that of soil moisture, but this kind of influence attenuation is relatively slow, seepage appeared to not occur significant effect; Very fine sand plays an important role all along. This also means that the soil moisture condition is difficult to shake the very fine sand content effect on rill erosion process.(2) For the critical shear stress, although the values tested under the different soil water conditions was varied, it did not reach statistical significance. Under air dry and drainage condition, the importance of the sand content is higher than that of other soil properties, and the increase of clay content would improve the critical shear stress under saturated conditions.(3) For process parameters which changes over time such as flow rate or flux, its change is restricted by the natural properties of the soil, the factors affecting the process are either directly or indirectly through the soil itself.(4) Under the saturated condition(seepage), the average values of interrill erodibility increased significantly; When it comes to the condition of drainage and air dry, there is no obvious difference between the two, even though the former is slightly higher than the latter. > 0.25 mm water stable aggregates content(%) is the only soil property that correlate with interrill erodibility when the soil water conditions is air dry; Very fine sand content and silt content are associated when it comes to drainage;under saturated condition there is no correlation, silt content(g/kg) wandering on the edge of the significant(P = 0.053).(5) The influence of soil water conditions on interrill erotion process can be significantly greater than the influence on rill erosion process, especially when the seepage appeared.