Using soil E horizon in salvaged topsoil material – effect on soil texture

Abstract

AbstractSoil is a limited natural resource that needs to be efficiently salvaged during landscape construction operations for its further use as topsoil. To avoid inclusion of undesirable subsoil material (e.g. excess clay from Bt horizon), the majority of current guidelines define borrowed topsoil material as the surface layer of native soil, or the soil A horizon. Using information from over 7000 soil pedons from the 48 contiguous United States, we characterized selected topsoil properties and simulated the mixing of A and E horizons. The selected soil properties were compared among four different operationally defined topsoils: A surface layer, ASL; AP surface layer, APL; A horizon, A; and a mix of A and E horizons, AE. Average topsoil depth decreases in the order: AE > A > APL > ASL; sand content decreases in the order: ASL > AE > A > APL; clay decreases in the order: APL > A > ASL > AE; and organic carbon decreases in the order: ASL > A > APL > AE. On average, mixing of A and E horizons increases excavation depth by over 2.5 fold while having minor effects on soil texture; with AE/A ratio of 1.03, 1.00 and 1.07 for sand, silt and clay content, respectively. Yet, average soil organic matter content decreases by 38% upon mixing A and E horizons. Given the marked increase in soil volume and minor effect on soil texture, it is our suggestion that, for landscaping purposes, protocols for salvaging excavated soil material, for reuse as topsoil material include the E horizon (where it exists). Supplementing the recovered soil material with organic matter, such as compost, to overcome its dilution due to the incorporation of E horizon is recommended.