The Theory of Sandy Land Soil Hydrology and Mode of Low Coverage Afforestation in Northwest China

Author(s): Mingyuan Wang

Most of the sandy land areas in northwest China belong to semi-arid area and the average annual rainfall is about 250-500 mm. Sandy land has the potential to reverse itself when man-made pressure is removed. The specific permeability structure of sandy soil showed heterogeneous anisotropy in the horizontal direction (x or y) of the soil surface (0-10cm) and showed interlayer homogeneity and isotropy in the vertical direction (z) of the underlying of soil surface, which formed rainfall infiltration process of the special combination of both channel flow and capillary flow percolation systems in sandy soil. It is reflected in the combination structure of "source" and "reservoir" in the soil water profile due to lateral gravity water recharge. There is no hydraulic relation between large area exposed sandy land and groundwater, and the model of shrub community consuming soil water reflects the relationship between soil water deficit and free gravity water recharge in sandy land formed by precipitation. On the one hand, sandy land afforestation preserves a part of bare sandy land intermittently to gather surface and subsurface soil runoff (or called collecting internal drainage from source) and adopting sandy land afforestation methods and techniques with low coverage and patch vegetation configuration. On the other hand, shrub plants in sandy land have a higher root-shoot ratio. According to the balance between soil water storage (collection) and vegetation water consumption, plantation vegetation coverage in sandy land can be determined by the square of root-shoot ratio . This formula indicates that the deep roots and horizontal ductility of plants in sandy land expand the soil water space available to vegetation under drought conditions so that the water consumption of transpiration is relatively supplemented. These two aspects are the key to the success of large-scale desertification control and afforestation.