Variability of soil carbon in row crop watersheds with agroforestry buffers

Abstract

Good understandings of soil carbon (C) variability are important to develop mitigation strategies for global warming and for enhanced ecosystem services. The objective of this study was to examine agroforestry, corn-soybean (row crop; control) and landscape effects on variations in soil C. One-m deep soil cores were sampled from two paired watersheds under agroforestry management with buffers and corn-soybean rotations and soils were analyzed for soil C, texture, pH, and cation exchange capacity. To observe the effect of landscape positions, both agroforestry and control watersheds were divided according to the landscape positions and area. The agroforestry watershed was divided into 0–2, 3–5, and 6–9 % slope segments and control watershed into 0–2 and 3–9 % slope segments. The results showed non-significant higher values of soil C in the agroforestry watershed after 3 years of establishment compared to the control treatment. Coefficient of variation (CV) showed ranges of variability for soil C by soil depth in both watersheds. Soil C distribution under agroforestry (CV 0.19–0.31) was moderately variable whereas under control (CV 0.30–0.40) it was moderate to most variable. Significantly higher amounts of soil C were observed at lower landscape positions compared to the upper and middle positions probably due to the depositions of eroded plant materials and retention by the grass waterway. Similarly, higher soil C was observed on both watersheds where depths to the claypan were shallow. It might be due to the lower drainage and soil water movement. Establishment of agroforestry practices decreased the variability of soil C, helped increase the soil C during long run as well as helped to enhance the ecosystems services.