The Process of Soil Desiccation under <i>Haloxylon ammodendron</i> Plantations: A Case Study of the Alxa Legue Desert, China

<i>Haloxylon ammodendron</i> is a desert shrub widely used as a windbreak and for sand fixation, and it has achieved remarkable results in China. However, in desert areas, large-scale afforestation increases soil water consumption and forms a dried soil layer (DSL), the development of which seriously threatens the sustainable development of the ecosystem. In this study, soil moisture in the 0–400 cm soil profile was measured in selected 5-, 11-, 22-, 34-, and 46-year-old plantations of <i>Haloxylon ammodendron</i> plantations in Alxa Legue, China, and three soil desiccation evaluation indices were calculated—the soil desiccation index (SDI), DSL thickness (DSLT), and DSL soil water content (DSL-SWC)—to analyze the change pattern of the soil water content for different stand ages. The results showed that the shallow water layer (0–200 cm) was depleted sharply in the first five years of <i>Haloxylon ammodendron</i> plantation growth, but no DSL developed; the inflection point of soil water content change appeared after 10 years of growth, after which the shallow soil water was depleted and the drying process of the deep soil water content was significantly faster than that in the early growth period. The deep soil layer (200–400 cm) was depleted seriously after 22 years of afforestation, the soil drying phenomenon was obvious, and the DSL developed from the 172 cm soil layer. After 46 years of afforestation, the DSL was fully developed and the DSL-SWC was only 0.034 cm³ cm⁻³. Priority should thus be given to the use of less water-consuming shrub species; alternatively, after 5 years of growth of <i>Haloxylon ammodendron</i> plantations, certain water control measures should be taken to maintain the soil water balance.