Factors that Influence the Vertical Distribution of Soil Water Content in the Critical Zone on the Loess Plateau, China

Abstract

In arid and semiarid regions, determining the vertical distribution of the soil water content (SWC) in the Earth’s Critical Zone is important for understanding hydrological processes and for evaluating soil water storage (SWS) levels. However, the vertical distribution of SWC and its storage in deeper layers are unclear due to the difficulties associated with soil sampling. In this study, we investigated the vertical distribution of the SWC and SWS, and analyzed the relationship between SWC and related soil properties, including bulk density (BD), sand, silt, clay, and soil organic C (SOC), from the top of the soil profile to the bedrock at five sampling sites on the Loess Plateau in China (Yangling, Changwu, Fuxian, An’sai, and Shenmu) by soil core drilling. The results showed that the SWC variations at the five sampling sites tended to become weak as the depth increased. The mean SWC of all sampling sites exhibited a decreasing trend from south to north, with a significant difference ( < 0.01). Stepwise multiple regression analysis and state-space modeling showed that the BD was an important factor that affected the variations in the SWC in the deep soil layer. The trend of vertical distribution of the SWS was similar to that of the SWC. The results of this study deepen our understanding of the water conditions in deep soil layers, as well as the evaluation of SWS on the Loess Plateau in China.