Effects Of Changes Of Soil Water Storage And Hydraulic Conductivity Caused By Water Erosion On The Red Soil Seasonal Drought

The seasonal drought in summer and water erosion in spring seriously hinders the development and use of Red Soils in China. Water erosion has changed the physical and chemical properties of Red Soils and leades to reduce infiltration rates, increases surface runoff, decreases water content and soil water storage, at the same time when the water content in the low decreases hydraulic conductivity, increases difficulty in deep water, depending on surface water can not absorb enough water, thus increase the development of drought. In this paper, the research object was Red Soils, six treatments (Straw mulch, PAM, Bahia grass and combinated treatments) were texted. Their water content and storage were observed, and after the harvest soil water characteristic curve and hydraulic conductivity curve were determined, cleared the characteristics of seasonal drought in Red Soils, in the meanwhile, simulated the soil water flux in dry red soil root zone areas, researched the mechanism and impact of seasonal drought. These research results are as followed:1. Soil water moisture and storage is different with the six treatments. In the drought period, the soil water storage of 0-8cm and 8-15cm is speedly low, while the soil water storage of 15-30cm and 30-45cm is slower, but much more volatile. During the rainfall Straw mulch and PAM can make the surface (0-8cm and 8-15cm) store more water, but the deeper (15-30cm and 30-45cm) is not clear, Bahia grass in the surface is relatively poor. During the rainfall the soil water storage of 15-30cm and 30-45cm differes little, the six treatments are close to the soil water maximum storage, indicating that the rainy season makes the deeper storage at or near the saturation state, even if the adopted water conservation measures, the deeper impact is relatively small.2. The six treatments can change the nature of the soil hydraulic conductivity and water storage. By the soil water maximum storage of the water characteristic curve, we can see that during the rainy season and dry season the soil water maximum storage is different with the six treatments. During the rainfall Straw mulch and PAM can make the surface (0-8cm and 8-15cm) store more water maximum effective storage, but the deeper (15-30cm and 30-45cm) is not clear. Straw mulch in times of drought can maintain the water maximum storage of the soil and inhibit the excessive evaporation of soil moisture, which gradually eased the drought, but the effects of straw mulch is better in depth more than in the surface. By hydraulic conductivity curve we can see that PAM and Bahia grass increaseing the the soil hydraulic conductivity and water storage is worse than straw mulch, and with the decreasing of soil water suction, this difference is gradually increasing.3. After a period of continuous rainfall in drought soil water flux of the six treatments will gradually show a parabolic trend. Straw mulch can increase the soil water flux, but the other treatments are not clear. When the soil moisture is high, with the continuous surface evaporation 15cm-25cm can effectively compensate the loss of water caused by evaporation, but the compensation of 25cm-35cm to 15cm-25cm on the capacity of water supply is diminishing, forming the water supply lack of the layer, so after a period crops cause drought gradually. When the soil moisture is low, with the continuous surface evaporation 15cm-25cm can not effectively compensate the loss of water caused by evaporation, although the compensation of 25cm-35cm to 15cm-25cm layer of soil on the capacity of water supply is increasing, it does not effectively alleviate the water loss, Thereby increases the drought of crops.