Age- and Drought-Related Variation in Plant-Available Water of Rain-Fed Jujube Orchards on the Loess Plateau of China

As an important part of the large-scale ecological restoration project of “Grain for Green”, the planting area of jujube (Ziziphus jujuba) trees has increased significantly in the hilly region on the Loess Plateau of China, which aims to improve water and soil conservation and develop economic prospects of the region. Understanding the long-term effects of expanding orchards and the responses of soil water dynamics to drought are important for orchard management. Therefore, we use a space-for-time substitution to investigate the variations of plant-available water storage in returning cropland to orchards with different stand ages (2, 6, 10, and 15 years) in a normal year (NY2014, 442.1 mm rainfall) and the next year with low annual precipitation (DY2015, 388 mm rainfall). The results showed that the plant-available water storage in jujube orchards decreased with increasing stand age, and the trend was most obvious in the 60–180 cm layer. The mature stands (10 and 15 years) primarily absorbed soil water from the deep layer (180–300 cm) in DY2015, leading to negative values of plant-available water storage. The whole soil profiles were all subjected to severe water deficits in our study. The findings will help guide rain-fed orchard management in the loess hilly region of China and similar dryland regions