Abstract: Soil water balance of the artificial forestland planted with locust trees has been studied quantitatively for years on the water balance plots sets in Ansai soil and water conservation station of loess hilly region in Shanxi province, based on the soil water balance equetion for the soil of artificial forestland. The analyse result shows that the soil is becoming dry because of intense evapotranspiration and the water-sucking effect due to the development of the root system in deep layer if the artificial forest is made on the loess hilly region with semi-arid climate. The providing function of the water stored in deep layer to adjust the need of water from trees will be vanished, thus, only could the trees grow depending on the precipitation in current year. From this point of view, it is thought that the artificial forests deteriorate their own soil water condition constantly, which makes the trees grow slowly and limits the growth amount with water.

Key words: Soil water balance, The water stored in deep layer, Canopy interception