The influence of vegetation recovery on organic carbon and nitrogen distribution in surface soil particle of dry area

Adopting the physical separation technique to gain different soil particle size component in the process of vegetation recovery, and determine the contents of organic carbon and total nitrogen in each component. The increase of the content of silt and clay (0.05mm) and the decrease of the content of sand grains (0.25~0.1mm) led jointly the fining of soil texture in surface soil layer; the fining of soil texture was accompanied with the fixed existing effect of organic carbon and nitrogen, with marked effect (P0.05) after 20 years of fixed sand. The content of sand grains(0.1mm) in topsoil exhibits a significant negative correlation with organic carbon and nitrogen contents (P0.01), but the contents of very fine sand (0.1~0.05mm) and the content of silt+clay (0.05mm) showed marked positive correlation (P0.001). The reason of the above results was that the contents of organic carbon and nitrogen combined with each particle size in surface soil layer all increased in relation and their contribution degrees were in the order: silt and clayvery fine sand sand grains. The increase in the silt and clay content surface soil layer in the vegetation restoration processes played an important role to the fixed existing of organic carbon, and nitrogen, and the soil physical stability also increased with the increase in the organic matter content and silt and clay contents in the soil.