The effects of trees on soil properties and carbon storage in spatially distributed agroforestry systems in northwestern India

The impact of trees on soils is diverse, varying based on tree species and environmental conditions. To better understand the functionality and services of agroforestry systems, we assessed the impact of trees on soil properties and carbon storage in 14 traditional agroforestry systems in Rajasthan, India. Trees were counted for species and density, and were measured for height, diameter at breast height (dbh), and canopy diameter in 0.5 ha plots on 84 farmlands. Soil pH, electrical conductivity (EC), organic carbon (SOC), total nitrogen (TN), available phosphorus, and exchangeable potassium were assessed for samples collected at 1 m from the tree, the canopy edge, and 5 m away from the canopy edge as a control. Soil variables differed significantly between systems and distances from the trees. SOC, TN, phosphorus, potassium, and C-stock showed + 2.3–25.0% increase, whereas pH/EC decreased beneath the tree canopy compared to the control. P. cineraria , P. juliflora , and A. indica exhibited high SOC, TN, phosphorus, and potassium, respectively. Soil pH and EC were low under A. excelsa . Most soil variables increased with an increase in tree size. Rainfall negatively impacted soil pH, EC, and potassium. Climate significantly influenced the distribution of agroforestry systems, and the growth and dynamics of the dominant trees within these systems were key drivers for improving soil nutrients, properties, and carbon storage. These findings suggest that integrating trees into farming systems through planting can improve soil fertility, enhance carbon storage, and help restore degraded farmlands, contributing to both sustainable agricultural production and climate change mitigation.