The trade-off between soil water recovery and nitrate leaching following the orchard-to-cropland conversion in the Chinese Loess Plateau

A large-scale conversion of apple orchards into farmland has occurred in the tableland region of the Chinese Loess Plateau due to the aging of apple trees and the increase in pests and diseases. However, the impact of this conversion on soil desiccation recovery and soil nutrient transportation remains unclear, posing a new challenge for sustainable agricultural development in the region. The study employed the space-time substitution approach to select a long-standing orchard and croplands that has been growing maize for 1-, 3-, 5-, and 10-years post-orchard conversion as sampling sites, to investigate the effects of recovery durations of orchard-to-cropland conversion on deep soil water recharge and residual nitrate dynamics, as well as the key factors driving these changes. The results indicated that within 5 years, the conversion led to a rapid recharge of desiccated deep soil (6–9 m), followed by a stable and slow increase in subsequent years. The annual soil water recovery rate in the deep soil was as high as 5.90 mm m −1 a −1 . While, the increased water input also caused rapid leaching and accumulation of nitrate in the deep soil, with its peak depth increasing significantly from 3.4 m to 7.0 m over time (R 2 = 0.92). Soil water was identified as the key factor influencing nitrate leaching, with a correlation coefficient of 0.48 ( P