Soil drought and water carrying capacity for vegetation in the critical zone of the loess plateau: A review

The Loess Plateau (LP) of China is a good representative area for critical zone (CZ) science studies. The LP is famous for its deep loess. In most areas, the thickness of the loess profile is deeper than 100 m, and two-thirds of the area is arid and semiarid. With the Grain-for-Green project, the vegetation of the plateau has recovered gradually. However, with the increase in vegetative coverage, especially the planted vegetation, the water content of the soil profile has decreased and the soil is much drier. In this review, particular emphasis is paid to the dry conditions of deep soil, drought, regional restoration of vegetation, and effective management of soil moisture. We reviewed the progress of research on dried soil layers (DSLs) that resulted from soil drought in the past decades on the Plateau, and then we summarized the development of the concept and models of soil water carrying capacity for vegetation (SWCCV). This review is helpful for understanding the development of DSLs, optimizing soil water management through vegetation mediation, and designing a long-term sustainable framework for water-limited ecosystems.