Impacts Of Regional Weather Conditions On Soil Degradation In Rocky Desertification Areas

Soil degradation includes a complicated process of structural degradation, a loss of soil-water capacity and soil infertility which in turn induces the deterioration of the retentions of soil water, nutrients dissolved in water and airs in soil voids, which directly inffluece the growth of plants and crops. Due to their lamina form and low vegetation coverage in southeast karst areas, China, the ecological characteristic of surface soils are extremely easy to be affected by the external factors. Under the concentrated rainfalls and intermittent drought weather conditions, cultivation soils experienced successive dry-wet cycles, and show a swelling-shrinkage behavior macroscopically, which causes the soil hardening phenomenon, changes of microsturcture, finally has an impact on the soil properties(water retention capacity), and induce the degradation of soil-water capacity.Based on the analysis of years of weather records in karst rocky desertification areas, osmotic method(low suction range) and vapour equilibrium technique(high suction range) are employed for lab measurement of SWCC and the soil water characteristic of cultivation soil in Xiuwen district, Guizhou province is investigated. After that, a new equipment was developed for the test of soil volume changes under stress and suction control. The range of dry-wet cycle is determined according to the insitu weather records in study area. The porosity degradation model of cultivated soils in karst rocky desertification areas under regional weather conditions was then established correspondingly. Results show that, the air-enter value for the test soil is about 70kPa, residual saturation degree value is about 18%, the SWCC for desorption process shows clearly in step-phase, soil cumulative compression strains increase and soil void ratios decrease as the increase of drying-wetting cycles, which means the soil is gradually compacted.Finally, based on the investigations of the micro-mechanism under cyclic dry-and-wet effects which induced the loss of soil water capacity, and soil hardening, a void ratio attenuation law was proposed under the impact of weather changes in karst rocky desertification area. The research reached the target plan, the achieved findings have practical significance, and can supply experiences and references for some similar areas.