Abstract: Precipitation, the only water resource available for plants, is the main limited factor to plant growth in Shapotou area. After the vegetation protective system is built, the proportion between various components of water balance changes and exerts a great influence on growth and succession of artificial vegetation. By calculation on the basis of water balance using weighing electronic lysimeters, the results showed that the average precipitation (186.6 mm) met the need of plant growth in the earlier stage of sand control. The evapotranspiration of desert plants, of which the density is 75 in 100 m2 area of the ground, was much more than the annual' average precipitation. The ratio of evapotranspiration of Artemisia ordosica Kraschen. and Caragana korshinskii Kom. to precipitation was 136.6% and 131.1 % respectively. The ratio of soil evaporation in the water equilibrium rose as the precipitation decreased in the range of 100 ～ 200 mm. However when precipitation was around 100 mm, which was the lowest limit of precipitation available for artificial vegetation, water was almost solely dependant on the soil ineffective evaporation. The effects of precipitation distribution in time and space and formation of biocrust on the soil surface on water balance and water use in artificial vegetation were highly appraised.

Key words: Sandy soil, Water balance: Precipitation, Artificial vegetation: Evapotranspiration