| In the hilly red soil region, seasonal droughts occur frequently, and the water and nutrient retention capabilities of dry slopes are relatively weak. Long-term water and fertilizer management significantly impacts the physical and chemical properties of orchard soils. This study focuses on the Fangtai watershed in Xingguo County, Jiangxi Province, selecting navel orange orchards with different planting durations (3 years, 5 years, 7 years) and a forested control plot to analyze changes in soil organic matter (OM), organic carbon (OC), total nitrogen (TN), total phosphorus (TP), total potassium (TK), ammonium nitrogen (NH4+-N), nitrate nitrogen (NO??-N), available phosphorus (AP), available potassium (AK), pH, and soil particle size. The results indicate that navel orange cultivation significantly affects soil pH distribution. Forest soil pH increases with soil depth, whereas orchard soil pH shows the opposite trend. In the 0.5-0.7m soil layer, the pH of 3-year, 5-year, and 7-year orchards decreased by 5.9%, 12.8%, and 8.1% respectively compared to the forested land, indicating significant acidification in deeper orchard soils. The increase in orchard planting duration promotes soil nutrient accumulation. The OM, OC, TN, TP, and TK content in the surface soil of 7-year orchards was significantly higher than in the forested land, 3-year, and 5-year orchards, suggesting that long-term orchard management is beneficial for enhancing soil fertility. The content of NO??-N, AP, and AK also significantly increased with the duration of orchard cultivation, with accumulation intensifying in deeper soil layers, posing a potential threat to groundwater environments. Changes in soil particle size between forested and orchard lands were relatively minor, with forested soil having the highest clay content and 3-year orchards having the highest sand content, indicating a potential risk of soil erosion in the early stages of orchard establishment. Long-term orchard management has a dual effect of promoting soil nutrient accumulation and exacerbating acidification, highlighting the urgent need for comprehensive management measures centered on soil conservation, enhanced monitoring and regulation of deep soil nutrient dynamics, and ultimately achieving synergistic improvement in orchard production and ecological health in the region. |