Spatial variability in organic carbon stocks on level sites: Relation to vertical penetration of the A horizon

Understanding the source of spatial variability in soil organic carbon (SOC) stocks will contribute to improved sampling strategies to detect changes in stocks. Most of the variability in SOC stocks in cores collected from small (2 × 3 m) level plots on seven soils with similar cropping histories was related to variation in A horizon depth. Increased variability in horizon depth within plots coincided with the development of zones where the A horizon penetrated to greater depths. Consequently, accurate estimates of SOC stocks cannot be made from shallow measurements at the soil surface (e.g., 10 cm) and minimizing the spatial variability in locations of repeated sampling is necessary when characterizing changes in SOC stocks.Key words: Carbon sequestration, soil organic carbon, spatial variability, soil profile, A horizon