Soil water and chemical characteristics of sandy soils and their significance to land reclamation

Long-term observations were made of moisture and chemical content changes in sandy soils at ten locations in China, located in five different climatic zones: hyperarid, arid, semi-arid, sub-humid and subtropical humid. These sandy soil zones were delineated based on their bioclimatic characteristics, aridity, mean soil moisture content and precipitation. Spatial and temporal variations in soil moisture and water balance components of the top 1 m soil layer were monitored in different sandy soils. The water balance equation for the top 1 m soil layer was defined as: DeltaS = (P+M)-E in the hyperarid and and areas, DeltaS= (P+U)-(D+E+T-R) in the semi-arid areas, and DeltaS+DeltaV = (P+U)-(D+E+T-R) in the semihumid and subtropical humid areas. Sandy soil organic matter content (OMC), CaCO3, and soluble salts content were also investigated. Afforestation and a selection of land management techniques are suggested to slow or stop the development and expansion of sandy lands. In China, four land management regions, defined by the prevailing natural conditions and complexity of reclamation/mitigation techniques implemented are: Region I: trees and shrubs to fix shifting sands, land can then be used for high-profit agriculture and commercial crops; Region II: some species of shrub plants and grasses to fix shifting sands; Region III: mechanical methods to enhance biological methods to fix shifting sands; Region IV: improvement of afforestation practices, and stabilization of low-lying wetland sites, engineering works, and irrigation systems. The results of such programs have important implications in terms of the economic benefits of irrigated agriculture and environment of sandy lands in China. (C) 2002 Elsevier Science Ltd.