根据咸阳庞西村苹果林地、梧桐林地和草地土壤含水量测定,研究了0~6m土壤含水量的变化和土壤干层特点与分布。结果显示, 咸阳人工林地从表层向下含水量呈现由高到低再到低的变化;10龄苹果林地2~4m深处土壤含水量平均为8.3%,12龄梧桐林2~4m深处土壤含水量平均为8.6%,均发育了明显的土壤干层;4龄苹果林下土层有干化显示,但无干层发育;草地土层含水量明显较苹果林地高,无土壤干化的显示。研究表明,土壤干层形成的具体原因一是降水量少决定的薄膜水带埋藏深度小,二是薄膜水的运移速度缓慢和含水量低。为保持人工林基本正常的生长和土壤水的正常运移,应避免严重的土壤干层出现。咸阳附近土壤干层的出现表明土壤干层在黄土高原广泛分布,该区的植被恢复首先应以疏林或森林草原为主,待土壤水分改善后再考虑恢复森林植被。

According to soil moisture content determination of apple forest land and the Chinese parasol forest land at Pangxi and Dongshi villages in Xianyang, the change of 0-6-m soil moisture content and the characteristic and the distribution of dry soil layers were studied in this paper. The result shows that the soil moisture content in 6-m soil profile under artificial forest in Xianyang is high in the upper layer and becomes low in the middle and then become high in the lower layer; mean soil moisture content is 13.2% in 0-1-m earth layer under 10-year apple forest, 8.3% in 2-4-m earth layer, and 10.8% in the 4-6-m earth layer. Mean soil moisture content under Chinese parasol trees forest grown for 12 years is 12.8% in 0-1-m earth, 8.6% in 2-4-m earth layer, and 12.2% in the 4-6-m deep earth layer. Mean soil moisture content is 12.4% in 0-1-m earth layer under 4-year apple forest, 11.9% in 1-4-m earth layer, and 13.6% in the 4-6-m earth layer. Mean soil moisture content is 12.3% in 0-1-m earth layer under grassland, 13.2% in 1-4-m earth layer, and 14.5% in the 4-6-m earth layer. The change of the above mentioned indicates that, dried soil layer develops in 2-4-m earth layer under 10-year apple forest and 12-year Chinese parasol trees forest; soil drying also occurs in 2-4-m under 4-year apples forest, but has no the development of dry soil layer. The soil moisture content is obviously higher in grassland than in the apple forest land, soil drying does not occur in grassland. The research result indicated that one of development causes of dry soil layer is that burial depth of film water belt is small, which is decided by the a little precipitation; anthor is slowly moving speed of the film water and low moisture content. In order to maintain normal growth of the artificial forest and the normal circulation of soil water, we should avoid the development of serious dry soil layer. The development of the obvious dry soil layer nearby Xianyang indicates that the soil drying layer is distributed widespread in the Loess Plateau, and the vegetation reconstruction in this area should first develop the thin forest or the forest-steppe, then restore the forest vegetation after the soil moisture improvement. Taking the project measure and improving soil structure, enhancing soil permeability, also can increase burial depth of film water belt and reduces the development intensity of dry soil layer.