The Variation of Surface Aggregates in the Degradation Process of the Dry Red Soil in Jinsha River Dry-Hot Valley

Abstract-Jinsha River Dry-hot valley is the typical region of soil degradation in southwest of China. In order to understand the mechanism and the effect of the soil degradation, sampled the dry red soil from the Jinsha River Dry-hot valley, researches and analysis were made in the surface 0~20cm soil aggregates under the four different covers. The results indicated that: (1) The surface soil aggregate stability and other physicochemical properties became deteriorated, the anti-erosion ability got weak and the organic content was reduced in the degradation process of the dry red soil from vegetation to no vegetation. (2)> 0.25mm water stable aggregates content (WSAC) and mean weight diameter (MWD) gradually increased, but the fractal dimension (FD) gradually reduced in the process of barren→ rare-tree shrub → shrub → grass; (3) The percentage aggregate destruction (PAD0.25) demonstrated: grass < shrub < rare-tree shrub < barren; (4) The variation of the soil aggregates was not obvious between shrub, rare-tree shrub and grass. The research also indicated that: (5) The stability index of water-stable aggregates (WSAC, MWD) showed an intensely significant negative correlation with bulk density, but significant positive correlation with total porosity. Soil organic matter promotes the stability and other physical properties of water-stable aggregates ， and vegetation conservation is the key to improve the structural condition of the dry red soil