Depth-Wise Assessment of Soil Fertility and Organic Carbon under Different Land Use Systems: Implications for Climate Change Adaptation and Resilience in Smallholder Agroecosystems

This study investigates the influence of various land use systems (LUSs) on soil physico-chemical properties, nutrient dynamics, and soil organic carbon (SOC) stocks in the Central Plain Zone of Uttar Pradesh, India. Soil samples were collected from six distinct LUSs, i.e., fallow, crop-based, horticulture-based, forest-based, vegetable-based, and barren land, and analyzed across three depth intervals (0–15 cm, 15–30 cm, and 30–60 cm). Soil pH increased steadily with depth, ranging from 7.43 to 8.58 at the surface layer to 7.55 to 10.32 in deeper layers. Horticulture-based LUSs recorded the lowest pH, while barren lands had the highest. Electrical conductivity (EC) also rose with depth, ranging from 0.12 to 3.63 Mgm-1, at the surface to subsoil layers, all below critical salinity thresholds. Soil organic carbon (SOC) content decreased with increasing soil depth across all land-use systems. Among the studied systems, horticulture-based land use recorded the highest SOC content (0.77%), whereas barren land showed the lowest SOC content (0.21%).”Due to greater organic matter inputs and reduced disturbances, horticultural systems also exhibited significantly higher levels of macronutrients (N: 17.98 kgha⁻¹, P: 330.45 kgha-1, K: 374.81 kgha⁻¹, S: 84.33 mgha⁻¹) and micronutrients (Fe: 164.12 mgha⁻¹, Mn: 60.89 mgha⁻¹, Cu: 2.85 mgha⁻¹, Zn: 1.80 mgha⁻¹). Bulk density increased slightly with depth (1.46–1.63 Mgm-³), while soil moisture content remained relatively stable (43.43% to 42.31%) with moderate variability (CV: 24–27%). The mean total SOC stock was 10.77 t C ha⁻¹, ranging from 5.44 to 14.46 tCha⁻¹. Microbial properties also varied among land uses: dehydrogenase activity (DEA), an indicator of microbial functionality, peaked in vegetable-based systems (30.54 µgTPF g⁻¹), whereas microbial biomass carbon (MBC) was highest in forest-based systems (184.83 µg g⁻¹). Correlation and regression analyses revealed a strong positive relationship between SOC and nutrient availability, with the highest correlation observed for Zn (R² = 0.99), followed by N (R² = 0.83) and K (R² = 0.75). Overall, barren lands showed the poorest soil quality indicators, while horticulture-based systems consistently demonstrated superior soil fertility and carbon sequestration potential. These findings emphasize the critical role of land use management in regulating soil fertility, SOC dynamics, and the long-term sustainability of agro-ecosystems in the region.