Changes in soil organic carbon, nitrogen and sulphur along a slope gradient in apple orchard soils of Kashmir Himalaya, India

Accumulation and losses of soil organic carbon (SOC), total nitrogen (TN) and sulphur (S) influence food security and global warming. Therefore, their spatial distribution and variability at regional scale, and their relation to topographical variables are of great interest. In this study, the variability of SOC, TN and S content was evaluated in apple orchard soils of Kashmir region, at three depths (D₁: 0-10, D₂: 10-20, and D₃: 20-30 cm) on slope gradient i.e.: flat, medium, and high. With an increase in slope, a significant decrease of SOC and TN was observed, with concentration of SOC and TN recorded highest (14.3±2.06 g kg^-1 & 0.97±0.35 g kg^-1) in flat slope orchards and lowest (9.6±2.07 g kg^-1 & 0.84±0.41 g kg^-1) in high slope orchards. On stock basis, the values recorded for flat, medium, and high slope orchards_, for SOC and TN were 54.62±4.24 Mg ha^-1 & 0.38±0.06 Mg ha^-1, 44.13±5.11 Mg ha^-1 & 0.32±0.09 Mg ha^-1, and 38.73± 5.94 Mg ha^-1 & 0.28±0.10, respectively. The differences for S concentration and stocks were modest, with flat (0.21±0.15 mg kg^-1 & 0.09±0.0.003 Mg ha^-1) > high (0.16±0.07 mg kg^-1 & 0.06±0.007 Mg ha^-1) > medium (0.12±0.04 mg kg^-1 & 0.075±0.009 Mg ha^-1). Across slopes, SOC, TN and S decreased with increasing soil depth, suggesting clear downward trend. Overall, SOC and TN increased with the increase of altitude, precipitation and clay content while its relationship with soil acidity and soil bulk density was negative. The findings may provide scientific basis to structure agricultural development plans or prioritize regions for soil conservation efforts.