Deep soil water storage and drainage following conversion of deep rooted to shallow rooted vegetation

Deep soil water management is important for agroforests to combat frequent droughts. However, little is known about how deep soil water (up to 15.0 m) and its deep drainage after trees fell evolves with time (< 20 years) in deep vadose zone. Therefore, this study was aimed at evaluating the impact of orchards removal on the replenishment of deep soil water and its deep drainage in a sub-humid region on the Loess Plateau, China (LPC). We established paired experimental plots between cultivated farmlands after deforested land and mature/aged orchards. Soil water storage and deep drainage were calculated from the measured soil water contents based on deep soil sampling (down to 6–15.0 m). Then, the time evolution of soil water storage and deep drainage rates were obtained based on the space for time substitution. Results showed that the replenishing front (indicated by the increase of soil water) deepened with time after orchard removal, which progressively increased deep soil water content. The drainage rates increased suddenly right after orchard removal and attained a constant value of 22.0 ± 3.1 mm yr−1 after the conversion. With this deep drainage rate, deep soil water deficit created by prior mature orchards would require 48–69 years of annual crop cultivation. Therefore, this study helps improve the further understanding of ecohydrological process under land use and management of deep soil water storage for increasing resiliency of agroforests to climate change.