| The project was carried out to study the changes of topsoil surface structure and the relationship between soil surface structural change and the soil erosion under simulated rainfall, by measuring erosion parameter and observing soil surface micro morphology during the process of rainfall. The red several soils, such as H1 H2 H3 T1 T2 T3, were derived from three different parent materials in hubei province .We hope to provide the theory for the loss of soil and water in southern hill in China.1. The textures of H1,H2,H3,T1,T2,T3 were clay loam, silty clay loam, salty loam, sand clay, sandy loam soil, sand loam soil. Soil erosion would change soil mechanic composition. As for H2 and H3 derived from quaternary deposits, the textures of soils would become heavy because of soil erosion, whereas T2 and T3 of red soil of granite became sandification. The breakdown of soil aggregates was the premise of soil erosion, and dispersion ratio explained the stabilization of soil aggregates of six experimental soils, which was calculated by the content of micro-aggregates. The DR of H1,H2,H3,T1,T2,T3 were 0.84, 0.68, 0.58, 0.62, 0.87, 0.92, And the order was T3>T2>H1>T1 H2>H3.2. The photos of soil micro morphology explained the development of soil surface structure during the process of rainfall. The results showed that, there were three phases including the preceding of runoff, preceding of runoff to stability of runoff, stability of runoff. The three phases revealed the development of soil structure, which was the process from loosen to tighten, from unstability to stability.3. Soil splash erosion is one of the most important parameters of soil erosion. The results showed that, the amounts of T2 and T3 were highest, and the rates of soil splash erosion were lower during the rainfall of 20min. The curve of H1was descending, and the others soils were ascending during prophase of rainfall, descending after 10min. The results of different particle size aggregates showed that, the curve of splash erosion of aggregates of <0.25mm was slowly ascending during the rainfall process, whereas, according to >0.25mm, the curve was ascending during prophase of rainfall, then descending. According to aggregates of different particle sizes, the splash erosion rate of 0.5~lmm aggregates was highest, and 2~3mm was lowest. The effect of splash erosion on sloping surface erosion is evident. After the splash erosion was eliminated, the erosion amount was less than half of the amount when the splash erosion existed. It indicated the splash erosion contributed more than 50% erosion amount, but to the different soil type, the contribution ratio of erosionamount varied, such as the soils derived from granite, the contribution ratio reached 70%.4. The order of the amount of steady run-off was HI (6644ml) >H2 (6045ml) >T3 (4953ml)>T2 (4585ml)>Tl ( 3507 ml ) H3 (3155ml) , and the order of sediment wasT3[17.365 g#(m2#min)-1] , T2[16.305 g#(m2#rnin)-1] Hl[14.149 g#(m2#min)-1]>H2 [9.038 g#(m2#min)-1]>H3 [2.686 g#(m2#min)-1], T1 [2.139 g#(nr2#min)-1]. There were two typical characters in the soil surface of H1 and H2, which were breaking up of aggregates easily and sharply tightening of surface soil. The two characters sharply enhanced the rate of sediment, then H1 descending, and there were several peaks in the curve of H2. The fine structure and stable aggregates deferred the destroy of soil surface structure, and the change of sediment was slow. The stability of aggregates of T3, T2 was very low and multilevel pore was few, so soil splash erosion and sediment was very high.5. Porosity of micro image of H1, T2, H2 was analyzed by IDRISI Software. The results showed that the order of Porosity was H1 |
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