关键词: 关中地区, 人工林, 干层分布, 重力水, 薄膜水, 生态环境

Abstract: Moisture content change and characteristic, distribution, formation reason of dried earth layer under artificial forest land and lawn ranging 0~6m depth in Guanzhong Plain were studied in this article by drying-weight method.The aim of the research is to verify the distribution scope of dried earth layer in the south of the Loess Plateau and the reason of it, and to provide scientific basis for the prevention and control of dried earth layer. Experiment results show that the average earth moisture content is 8.4% between 2 and 4m of 10 age apple trees, the average earth moisture content is 9.0% between 2 and 4m of 12 age phoenix trees in Xianyang. The average earth moisture content is between 9.3% and 9.5% between 1.8~3.6m of 12 age phoenix and poplar trees in Lantian. The average earth moisture content is 9.2% between 2 and 3.5m of 15 age apple trees in Wujiafen, and there is formation of dried earth layer between 2 and 3.5m. There is obvious formation of chronic dried earth layer in artificial forest land at Xiekou of Lintong and Weiqu of Chang'an.The average earth moisture content is more than 12% below 4m of the middle age artificial forest land, which indicates that the dried earth layer doesn't extend to the layer below 4m.The average earth moisture content is more than 12% below 2m of 6 age and 4 age apple trees land, and there is no formation of dried earth layer. According to the computation of CaCO₃ migration depth model, under 600mm annual precipitation condition in Guanzhong Plain, the migration depth of gravity water is less than 4m, which indicates that the dried earth layer in this area is chronic. The changes of the moisture content of the artificial forest land show that the dried earth layer is distributed extensively on the Loess Plateau, and the south boundary of it has reached the northern foot of the Qinling Mountains.In Northwest China, where annual precipitation is less than 600mm, the dried earth layer in the artificial forest land is a universal natural phenomenon. The formation reason of the dried earth layer is that the gravity-capillary zone depth, which is determined by precipitation, is obviously smaller than 2 m.The direct action of water factor of dried earth layer is that the buried depth of the zone is small and the water movement velocity is slow, while the high water consumption tree species is the vegetation factor of it. It is clearly shown that the depth of the gravity water and the capillary water in Guanzhong Plain is the main natural factor for the formation of the dried earth layers. Whether the artificial forest or natural forest, the dried layers generally develop in the middle age forest land. The formation of the dried layer doesn't mean that the forests can not develop in this area, but they cannot develop well.Trees can be planted in areas where dried earth layer developed poorly, but they are not suitable to be planted in areas where dried earth layer developed intensely.

Key words: Guanzhong area, artificial forest, distribution of dried earth layer, gravity water, capillary water, ecological environment