Assessing the response of orchard productivity to soil water depletion using field sampling and modeling methods

Soil water deficit in apple orchards is a common phenomenon related to land degradation on the Loess Plateau. However, little is known regarding the degree of soil water depletion and its effects on orchard productivity in rainfed apple orchards. We used a combination of field sampling and modeling to understand the impact of apple orchards on soil water availability and changes in orchard productivity over a long-term time series. A total of 51 soil profiles from eight experimental sites in the Loess Plateau, were collected in 2010 and 2016 and modeling was used to evaluate the long-term effects of apple plantations on soil water depletion and orchard productivity. A process-based model, the Environmental Policy Integrated Climate (EPIC), was calibrated and validated using survey data from field experiments. The calibrated EPIC model could well simulate soil moisture and orchard productivity with relative root mean square errors (RRMSE) of 11.12 % and 2.71 %, respectively. Field sampling and modeling showed that conversion from farmlands to orchards decreased soil moisture, leading to severe soil water depletion (SWD) in the 0–15.0 m soil profiles. Stand age was the main factor influencing soil moisture, and SWD gradually increased with increasing stand age. Depleted soil water led to land degradation and decreased orchard productivity, especially in water-limited regions. Simulation results suggested that the optimal planting density and fertilizer application rates were often related to variability in climatic conditions; therefore, appropriate management practices need to be adapted to local natural conditions. Although SWD in apple orchards is inevitable, the detrimental effects could be minimized during orchard development, provided that appropriate management measures are selected based on precipitation and soil water conditions. These findings may provide a basis for evaluating the extent of SWD and its effect on orchard productivity in dryland apple orchards.