Organic sulfur and the retention of nutrient cations in forest surface soils

Abstract

Sulfur and cation transformations were studied in A-horizon soils from 9 plots in Deer Run State Forest (DRSF) in southeastern Missouri on two dates, and from 27 plots of the Missouri Ozark Forest Ecosystem Project (MOFEP) near DRSF, seasonally for three years. The DRSF plots were chosen based on history of timber harvest; 2–3 yr and 8–10 yr post clear-cut, with controls about 40 yt post cut. Total C and S, organic sulfur (OS), exchangeable K+ and Mg2+, and rates of microbial OS production varied by season and year in surface soils from MOFEP plots. Exchangeable K+ concentrations were correlated with total C, total S, and OS. In clear-cut DRSF A-horizon soils, OS production was greatly reduced (p < 0.05) compared with controls. Exchangeable K+ and Mg2+ also were much lower in soils from clear-cut plots than in soils from control plots (p < 0.01). Cation exchange for OS compounds with sulfhydryl groups was only marginally greater than for organic matter of similar structure with no sulfhydryl groups. Overall, litter input appears to be a key to maintaining long-term surface soil OS, K+, and Mg2+ concentrations.