Abstract: Employing water balance equation,this paper estimated the evapotranspiration of different density Caragana microphylla shrubs during their growing season.The results showed that during this season,the soil water content under artificial C.microphylla shrubs decreased with their increasing planting density.The average soil water content of 0.5 m×1 m and 1 m×2 m density artificial C.microphylla shrubs was below wilting humidity (1.55%)，while that of 2 m×2 m density and natural shrubs was kept above 1.60% which could meet the demand of shrubs growth.The evapotranspiration increased with increasing planting densities,being the highest (297.81 mm) in 0.5 m×1 m density artificial C.microphylla shrubs,which accounted for 97.90% of the total rainfall during growing season,and the lowest (279.71 mm) in 2 m×2 m density shrubs.By the end of growth phase,soil water content had a surplus of 24.49 mm.According to the soil water status and water balance theory,the appropriate planting density of C.microphylla shrubs in Horqin sand land should be 2 m×2 m.

Key words: water resource, Gaoyou area of Jiangsu Province., hydrogen and oxygen stable isotopes, D-excess, meteoric water