Response of soil water in deep dry soil layers to monthly precipitation, plant species, and surface mulch in a semi-arid hilly loess region of China

Large-scale deep soil desiccation has occurred in the Loess Plateau caused by large-scale introduced vegetation rehabilitation over many years. Consequently, this occurrence has raised concerns among scholars regarding the obstacles to plant succession that may result from deep soil desiccation following large-scale artificial vegetation construction. In order to answer the question of whether vegetation can be replanted and water can be restored in the deep dry soil environment in this region, large soil columns in the field were used to simulate dry soil in the 0-1000 cm layer. Some soil columns were planted with Robinia pseudoacacia, Caragana korshinskii, alfalfa (Medicago sativa L.), jujube (Zizyphus jujuba Mill.), and Poa annua, while other columns were covered with stones, branches, ground cloth, and white plastic film. Bare soil columns were used as the control treatment (CK). Dynamic changes of soil water in the 0-1000 cm soil layer of the soil columns were regularly observed, and five years (2014-2018) of continuous observation data were analyzed. The results showed that: (1) Under the condition of severe desiccation of the deep soil layer in the semi-arid loess region of China, reintroducing plants can be successful, and the reintroduced plants can grow normally depending on the amount of local precipitation; (2) Due to the different water consumption amounts of reintroduced plants, a new soil water balance can emerge in the dry soil layer. Plants with high water consumption planted on dry soil can result in more severe soil desiccation, while plants with low water consumption planted on dry soil can alleviate soil desiccation. (3) The use of soil surface mulching had a strong effect on soil water restoration, with the order of effectiveness for soil desiccation remediation being white plastic film > ground cloth > branches approximate to stones > control (CK). In particular, the use of white plastic film can transform severely desiccated soil in the 0-640 cm layer into a non-desiccated state. These research findings directly address long-standing concerns of ecologists regarding plant succession and soil water restoration in deep desiccated soil, and can serve as a reference for the sustainable development of ecological construction in the Loess Plateau of China.