Abstract: To better understand the influence of artificial sand fixation vegetation on soil physical and chemical properties in the flowing sandy land of hill side, The soil nutrients and mechanical composition at the sand fixation vegetation restoration area (experimental group) and the bare land (control group) in the Shannan broad valley section were measured. The valley is located at the middle reaches of the Yarlung Zangbo River. The improvement effect of Hedysarum scoparium on the soil nutrients and mechanical composition was then analyzed. The results show that the pH and total potassium content of the Hedysarum scoparium rhizome soil decreased significantly, while the total nitrogen and organic matter content increased observably when compared with the control group soil at the same altitude. The ranking of quality of soil nutrients is total potassium > total nitrogen > organic matter > total phosphorus. The soil particle in the sample plot is mainly fine sand and medium sand, and the content of fine sand in the Hedysarum scoparium rhizome soil of flower stick (53.79%) is higher than that in the control group (49.34%), which indicates that the artificial flower stick can make the soil particle size continuously to be finer, and has an increasing effect on the nutrient content of the surface soil of vegetation. In the mechanical composition of soil, there was no correlation between coarse sand, extremely coarse sand, gravel and soil nutrients, however there was a high correlation between clay and very fine sand and soil nutrient content. The above findings show that the smaller the soil particles were, the greater the impact on the soil can be, which means the greater contribution to the soil nutrients. In conclusion, as a plant with developed root system, Hedysarum scoparium is helpful to improve the texture of the flowing sandy soil in the middle reaches of the Yarlung Zangbo River, and can be chosen as a high quality artificial restoration plant in the flowing sandy land.

Key words: Hedysarum scop arium, vegetation restoration, shifting sandy land, middle reaches of Yarlung Zangbo River