Soil moisture is crucial to plant growth and plays a vital role in vegetation restoration.Based on spatial pictures and databases,combined with sample soil moisture data and geographic data of Ansai by GIS,a method was developed to define the sample soil moisture ratio according to different combinations of land use type,land type and slope grade.Using GIS technique and maps were made for indicating the spatial variation of soil moisture in different soil layers.Using these maps,the amount and distribution of average soil moisture content in different soil layers in Ansai county were calculated.Quantitative analysis of the soil moisture structure demonstrated that soil moisture content in Ansai County was at a very low level as a whole.The soil layer from 0 to 500cm with soil water content between 8.6% and 10.8% accounted for 75.34% of total land area,and the area with soil moisture less than 8.6% accounted for 19.36% of the total land area,of which the area with soil moisture less than 6.4%(dry layer) accounted for 9.23%.The distribution of soil moisture content in soil profile showed that dry layer was mainly concentrated in a upper layer from 0 to 300?cm depth.
The area with soil moisture more than 10.8% just accounted for 5.31% of the total area.The amount of soil moisture content,or so called "Soil moisture reservoir capacity" in the layer from 0 to 120?cm deep is only 0.060.07?m~3/m~2,and were less than 0.15?m~3/m~2 in other layers.This indicated that the "Soil moisture reservoir" had limited capability to adjust for forest growth,and a large scale of planting was not suitable because its water consumption exceeded the supply of water from "Soil moisture reservoir".These findings showed that soil moisture environment was rather serverse in Ansai County,and could not provide much water for vegetation restoration.Therefore,more efforts should be laid on the improvement of soil water environment while following the principle of "selecting suitable tree species for sites" in planting.