Mechanical Stability Characteristic Of Red Soil Aggregates And Its Effects On Soil Splash Erosion

Red soil region in China with high weathering、strong leaching and strong biological cycle decided the vulnerability and unstability of red soil ecological system;Plus human impact, lead to the increasingly sharpen of soil degradation such as soil impoverishment, soil erosion, acidification and pollution. This study is for the serious soil erosion, based on broken theory of aggregates, to investigate the aggregate characteristics of mechanical stability and splash ersion process under the condition of rainfall simulation, which derived from Quaternary red clay and Shale; at the same time through the water stability analysis summarize the relationship between the mechanical stability and soil water stability. This study thorough research the effects of3-5mm aggregates mechanical stability on the characteristic of splash ersion under the condition of rainfall simulation, and reveal the intrinsic link between the crushing mechanism of soil aggregates and the splash erosion process. The main results were listed as following:1. The effects of land utilization and tillage frequency on soil mechanical stability were analyzed. Different land utilization, the soil derived from the same parent material, shear strength and penetration resistance showed the same trend:Tea garden>Plantlet>Arable land. The tensile strength of red soil aggregate decreased when aggregate size increased, but the penetration resistance increased when aggregate size increased; the same sizes aggregate, the mechanical stability of red soil derived from Quaternaryred clay was greater than shale.2. The effects of properties on mechanical stability were analyzed through soil basic physical and chemical properties. The results reflected the soil mechanical stability had a significant negative correlation with water content, but had a significant positive correlation with MWD of dry sieving. In the small particle size scale, the mechanical stability of aggregates had a significant positive correlation with iron oxide content.3. The correlation between the mechanical stability and water stability of soil aggregates results reflected that significant correlations were observed between mechanical stability and water stability of3-5mm aggregates. As mechanical stability of soil aggregates increased, the higher the content of original particle size of aggregates after wet sieving, mean weight diameter of fragments increased, WSA>0.25mm increased. The tendency that the water stability increased with increasing the mechanical stability of the same sizes aggregate; the high mechanical stability of soil aggregate had the stronger resistance to erosion, can be used as indicators of aggregate stability in the process of characterization of erosion.4. The mechanical stability of soil aggregate had the significant differences on the sensitivity of different broken mechanism, which is more sensitive to slaking caused by fast wetting. In the fast wetting process of3-5mm aggregate, with more sufficient mechanical stability, breakdown induced by slaking decreased, in other words, its water stability increased.5. The mechanical stability of soil aggregate had significant effect on the characteristic of soil splash ersion. The total splash loss proportion of soil aggregate derived from Quaternary red clay lower than Shale, because of higher mechanical stability. Under the same cumulative rainfall, the total splash loss proportion decreased with increasing aggregate size, which indicates that large aggregates are prone to break down to small aggregates but difficult to break again under rainfall destruction.6. Based on simulated rainfall, analyzed the broken characteristic of different mechanical stability3-5mm aggregates. The results reflected more sufficient mechanical stability, splash by rainfall decreased, the MWD increasing after rainfall; in other words, significant correlations were observed between mechanical stability and water stability of3-5mm aggregate, can be used as the index of aggregate stability in the splash erosion process.