为查明西安地区土壤干层和丰水年之后的土壤水分的恢复,利用烘干法研究了人工林地土壤含水量。结果表明,西安地区丰水年极端降水前杨树林,法国梧桐林、中国梧桐林和苹果林地大约1.5～4m深度范围内土壤含水量分别为9.3%、9.0%、9.7%和9.1%,普遍存在土壤干层,干层厚度约2.5m。丰水年之后土壤水分得到了很好的恢复,干层全部消失。经过1a左右的入渗,水分恢复深度可达6m左右。根据丰水年之后土壤含水量的不断消耗确定,西安地区丰水年之后一般经过3～4a左右的时间,人工林地的干层将会再次出现。发育弱的土壤干层并未影响到人工林的正常生长,表明在西安或与西安类似降雨量的黄土高原其他发展人工乔木林是可行的。

For making sure the dried layers of the soils and the moisture restoration after the high flow year in Xi'an area,using drying method the research has been carried out on the moisture content of the soils in the planted forests such as poplar,chinese parasol and chinar.The results indicate that the moisture content of the soils in the poplar,chinese parasol and chinar forestlands at a depth ranging from 1.5 to 4 m are separately 9.3%,9.0%,9.7% and 9.1% before extreme precipitation in the high flow year in Xi'an area.They are all lower than 12%,indicating that the dried soil layer exists under the condition of normal precipitation in Xi'an area.The dried layers develop widely with a thickness of about 2.5m.The soil moisture content from 0 to 6 m in the four planted forests has restored well after extreme precipitation in high flow year and the dried layer from 1.5 to 4 m have disappeared completely.Through about one year infiltration,the depth of the moisture restoration may reach to about 6m.After two years of extreme precipitation,the soil dried layers in the four planted forests still do not appear.According to the consumption of the soil moisture after high flow year,it is preliminarily determined that the dried layers in the planted forests will appear again after three or four years of high flow in Xi'an area on the basis that there is normal precipitation after the high flow year.In Xi'an area the soil dried layers in the four planted forests develop weakly.The weakly-developed dried layers do not affect the normal growth of the planted forest and the four planted forests such as poplar,chinese parasol and chinar grow well in Xi'an area,indicating that in Xi'an area or in other areas of the Loess Plateau with similar precipitation to Xi'an area planting arbor forests is feasible.