Comparative analysis of soil physicochemical properties under Melia composita- and Populus deltoides-based agroforestry systems and monoculture cropping

Introduction Soil degradation and declining soil organic carbon stocks pose major challenges to agricultural sustainability. Agroforestry systems are increasingly recognized for their potential to enhance soil quality, nutrient cycling and carbon sequestration, yet comparative information on Melia composita - and Populus deltoides -based systems under subtropical conditions remains limited. Methods A two-year (March 2021 - February 2023) factorial randomized block field experiment with six replications was conducted in the subtropical Jammu region of India to compare Melia composita - and Populus deltoides -based agroforestry systems across tree species, distance from the tree base and soil depth. The agroforestry systems were further evaluated against their respective adjacent monoculture cropping controls. Cowpea ( Vigna unguiculata ) and turmeric ( Curcuma longa ) were grown in rotation during each crop cycle. Eight key indicators-pH, electrical conductivity (EC), bulk density (BD), organic carbon (OC), available nitrogen (N), available phosphorus (P), available potassium (K) and soil organic carbon (SOC) stock were quantified. Results Among the two agroforestry systems, the Populus deltoides -based agroforestry system consistently exhibited superior soil properties, characterized by lower pH and bulk density, higher electrical conductivity and nutrient availability compared with the Melia composita -based agroforestry system. Significant spatial variations were observed within AFS, with soil quality significantly improving closer to the tree base and in the upper soil layer. After two crop rotations, both agroforestry systems showed increases in organic carbon, available nutrients and soil organic carbon stock relative to the first rotation. When compared with conventional monoculture, both agroforestry systems significantly enhanced soil organic carbon and available nutrients while reducing soil bulk density. Baseline soil properties at the two control plots were broadly comparable, with no statistically significant differences (p > 0.05). Pearson correlations confirmed strong positive associations among OC, N, P, K and SOC stock and negative associations of these properties with pH and BD. Conclusions The findings demonstrate that tree-based agroforestry systems, particularly those incorporating Populus deltoides , improve soil health, enhance system resilience and promote sustainable land management while contributing to carbon sequestration in subtropical agricultural landscapes.