Effects Of Wetting Rate And Aggregate Size On Erosion Processes At Hillslope In Three Red Soils

The red soil hilly region, located in the tropical and subtropical zones of Southeast China, consists of 9 provinces and 1 autonomous region. The area of region is about 1.13 million km~2, and hold 30% of the population. Because it has plentiful light, heat and water resources, the red soil hilly region has a high potential for agricultural and economic development. However, soil erosion and seasonal drought are major constraint for sustainable agriculture due to improper land use and uneven distribution of rainfall. Efficient rainfall use and erosion control, therefore, are very advantageous from eco-environmental and agricultural perspectives. Soil aggregate is a important part of soil and it's stability has substantial effects on soil porosity and, therefore, may influence infiltration rate and runoff processes under rainfall. The objects of this study were to investigate the relationship between soil aggregate stability and soil erosion at hillslope. In this study, three red soils derived from Quaternary clay were studied. The main results as followed:(1) There was a significant interaction between soil properties and soil aggregate stability. The aggregate stability by wet sieve methods ranked in the order of QP2,QP3,QP1. By the Le Bissonnais' method, the aggregate stability of different aggregate size and wetting rate is strongly different. As aggregate size increased, the aggregate stability decreased and the normalized mean weight diameter (NMWD) of different wetting rate is slow wetting, wet stirring, fast wetting.(2) There is a significant interaction between soil loss, runoff rate and aggregate size. The results showed that as clod size increased, the runoff rate decreased, ranging from 0.36 to 0.62mm min-1. The small aggregate size is likely to form a seal, consequently, the soil loss increased with decreasing aggregate size. There was also a significant interaction between soil loss, runoff rate and wetting rate. The results showed that as wetting rate increased, the runoff rate increased, ranging from 0.58 to 0.96 mm min-1. In each soil, thus, less soil loss was noted when exposed to slow wetting rate. A significant interaction between soil loss and runoff rate can be found. As the runoff rate increased, the soil loss increased too.(3)There is a significant interaction between sediment materials and aggregate size and wetting rate. During a rainfall, the largest MWD of sediment materials were found in aggregate size＜2mm of each soil. Wetting rate also played a great role in determining sediment materials. The largest MWD of sediment materials were found in fast wetting rate of each soil.