Spatial and temporal variability of soil organic carbon on a corn-soybean watershed with 23 years of agroforestry

Unsustainable agricultural practices deplete soil organic carbon (SOC), affecting ecosystem services, land productivity, soil health, and water quality. This study evaluated the long-term effects of row crop (RC), agroforestry buffers (AB), grass buffers (GB), and grassed waterways (GWW) on SOC. Agroforestry buffers (grass and tree) and grass buffer treatments were established in 1997 on a corn (Zea Mays L.)-soybean (Glycine Max [L]. Merr.) rotation. Grid soil samples from 86 locations were collected in 10 transects to determine SOC at 0-10 and 10-20 cm depths. The general linear model and the generalized linear mixed model were conducted to evaluate treatment, landscape, soil depth, and series effects on SOC. Kriging interpolation was used to visualize the temporal and spatial change of SOC in the watersheds, comparing samples collected in 2000 and 1994 with samples collected in 2020. The mean SOC percentage (SOC%) in the top 10 cm depth for the RC, AB, GB, and GWW areas was 1.94, 2.19 2.41, and 2.51%, respectively (rho < .001). The soil depth was significant (rho < .001) between samples from 0-10 cm and 10-20 cm. The mean SOC% among soil series showed no significant differences at the studied depths. The mean SOC% of 0-10 cm for RC, AB, and GWW were 1.85, 1.88, and 2.30% in 2000 and 1.94, 2.19, and 2.51% in 2020. The foot-slope position had the highest (2.41%) and the summit position had the lowest SOC (2.02%) percentages. The SOC% in the RC treatment from 0-10 cm at the summit, backslope, and foot slope positions were ranked 1.83 < 2.22 < 2.31%, respectively. Perennial vegetation and undisturbed land management practices increased SOC compared with the RC areas.