黄土高源沟壑区流域土壤干层的分布特征

以长武王东沟小流域为研究对象，从土壤干层的量化指标、分级评述和分布特征等3个方面初步探讨了黄土高原沟壑区小流域的土壤干层问题，并就小流域内的植被建设中的一些问题提出了几点看法。结果表明：在王东沟小流域内，土壤干层已成为一个普遍存在的水分现象，不同程度地影响植物生长和植被的恢复，并具有如下特点：①土壤干层的干燥化程度和干层厚度都表现为林地大于果园，果园大于草地，农地最小；②同一种植被类型由于密度、生物量、树龄、坡度、坡向以及坡位不同，其土壤干层的干燥化程度和深度也不相同。

Distribution characteristic of dried soil layer in Wangdonggou Watershed in gully region of the Loess Plateau

Dried soil layer results in soil degradation,slows down the vegetation growth rate,makes it withering,and imperils serious ecological environmental construction in northern China,especially in the gully region of the Loess Plateau.It has aroused our attention in recent years.Based on this phenomenon,dried soil layer in Wangdonggou Watershed in gully region of the Loess Plateau was studied in this paper.First,the measured indexes of dried soil layer are discussed according to the soil properties.The result shows that in Wangdonggou Watershed,the soil layer under2m with a moisture be-low14%can be regarded as dried soil layer.Second,according to the soil moisture profile and the degree of soil water conditions affect-ing vegetation growth,the dried soil layer can be divided into4grades such as non-dried,low-grade,medium-grade,and serious grade.Third,the distribution characteristics of dried soil layer in the watershed are analyzed.The result shows that dried soil layer is a general soil water phenomena in the whole watershed.In general,farm land>grass land>orchard land>forest land in the dryness degree and thickness of dried soil layer.In the same time,distribution characteristics of dried soil layer are affected by plant density,age,biomass,slope degree,slope aspect,and slope direction.Finally,some advices on vegetation construction are put forward:1)to adjust the land use structure,increase the proportion of rosebush and grassland to form a reasonable land use struc-ture;2)to develop the native tree categories to carry tree categories diversification off;3)to re-duce community density and control community productivity to assure a relative balance of water consumption and circumstance water supply;and4)in the process of vegetation regeneration and rehabilitation,the effect of ecologic niche on the distribution of soil water should be consid-ered fully to choose feasible category and keep reasonable vegetation density.