Effects Of Biological Crusts Under Sand-fixing Forests In Maowusu Sandland

This experiment is mainly based on the sand crust of YuLin Shaanxi District in MaoWuSu sand. Samples of the experiment are three sand crusts in which these areas different kind tree is planted and these samples are respectively measured to identify their physical and chemical properties of nutrients for seeking dynamic influence of sand crust to water movement in the desert. Major findings are as follows:1 Biological Crust in Maowusu District is mainly physical and mechanical powder sand (0.5~0.01mm) is its main ingredient, which is more than 85% of the composition. The water among the Sand Crust is two times as much as the bare sandy area and the minimum water holding capacity is also more than 60 percent higher of the bare sand.2 Biological Crust can function to fix nitrogen; there is a significant difference between the total nitrogen content in the crust and the control area, it is up to 2.62 times on average; organic matter content in biological crust is also higher than that of the control, when the vegetation cover is up to 60% of the crust ,the organic matter content will be 8.03 times as much as the control; P, K elements of biological crust are also higher than that of the control indicate the formation of crust to improve the soil nutrient status. pH value of S biological crust is connected to the species in the woodland. That is to say, different species will affect pH value of biological crust under it, so the pH value of different parts in the same forest is different from each other, and pH value is constantly decreasing from the top of sand dune to the bottom; it may be due to ground moisture and vegetation affected by light transmittance, the more water it holds and more dense vegetation it is covered, the more neutral pH of the under story crust is.3 Biological crust can effectively intercept the infiltration of rainfall. Because biological crust can control the speed of water infiltration, retention, and it is good to the restoration of vegetation. Biological crust can also slow down the speed of water evaporation. In the long dry season, so deep groundwater in the area of the biological crust will be saved.4 the contents of P are highly correlated with other factors. There is a positive correlation between the contents of the organic matter and the contents of the total N and the correlation coefficient is 0.95748; the level of correlation between K and P is very significant and the correlation coefficient is -0.98249; the negative correlation between K and the clay in the crust is also significant and the correlation coefficient is -0.9002.