Trees and grass buffers impact on soil carbon in an agroforestry alleycropping watershed

Perennial vegetation in farmlands can mitigate anthropogenic greenhouse gases (GHG) by capturing atmospheric carbon and storing it in the soil for extended periods. The objective of this study was to quantify soil organic carbon (SOC) concentrations and stocks under tree buffer (TB), grass buffer (GB), grass waterways (WW) and crop field (CS, corn-soybean rotation) to evaluate the significance of conservation measures in C sequestration projects. Soil samples were collected up to 1 m depth at upper, middle, and lower landscape positions from 26-year-old TB, GB, and WW in a watershed. The SOC concentration decreased with increasing soil depth for all four land uses. However, as expected, bulk density increased with increasing soil depth for all four land uses. It was highest for the CS land use. In 2023, for the depth of 0–10 cm, SOC increased by +0.63, +1.06, +1.37 and +1.63% in CS, GB, TB, and WW, respectively, since the land uses were established 26 years ago. Land uses had greater impacts on SOC stock in the top 50 cm depth, with WW (113.5 ± 12.9 Mg ha⁻¹), TB (106 ± 14.5 Mg ha⁻¹), and GB (102.4 ± 11.6 Mg ha⁻¹) compared to CS (90.9 ± 10.2 Mg ha⁻¹). However, at watershed level, with ~ 10% cover by TB or GB areas and the rest under CS, SOC stock up to 50 cm depth was respectively 91.6 and 91.2 Mg ha⁻¹ compared to 90 Mg ha⁻¹ by CS alone—1.3 to 1.8% increase. This is a significant increase in soil organic carbon across the landscape, which was realized with the conservation practices and agroforestry, while also playing a crucial role in protecting surface runoff in the landscape. Future studies may consider valuation of the overall ecosystem services due to the land uses (conservation measures) and the trees by considering optimization of incorporating such technologies in the farming systems to reduce negative trade-offs.