How Long-Term Orchard Management Revitalizes Soil Health beyond the Topsoil

Soil health is a key indicator of agronomic, economic, and environmental functions, yet its significance in deeper soil layers, especially in deep-rooted orchard systems, remains largely unexplored. This study examines soil health index (SHI) in topsoil and subsoil across various soil classes in long-term apple orchards. We measured 27 soil health indicators to develop a soil health framework for apple orchards using 240 soil samples. Significant differences (p < 0.05) were found between topsoil and subsoil for most indicators, including soil stability index (93 to 132%), organic carbon (100 to 130%), macronutrients (40 to 147%), and heavy metals (8 to 75%), while bulk density (1 to 5%), total soil pore spaces (4 to 12%), pH (0.03 to 0.12 unit), calcium carbonates (6 to 21%), and cation exchange capacity (7 to 18%) showed no significant differences. In the topsoil, the liner-SHI and non-linear-SHI scores ranged between 0.5 and 0.9 and 0.3 to 0.6 compared with the subsoil with corresponding ranges of 0.4 to 0.77 and 0.32 to 0.56, respectively. Both the liner-SHI and non- linear-SHI scores were higher in the topsoil, explaining 25-29% of the variance in apple productivity. Our results bring further insight into a quantitative method for assessing soil health at the soil type-scale and creatively analyzes the changes of SHIs with soil depth and their relationship with product performance in the apple orchards under long-term continuous intensive practices.