Sequential Burning Effects on the Soil Chemistry of a Grassland Restoration in the Mid-Atlantic Coastal Plain of the United States

Prescribed burning is a common management tool used in grassland restorations to improve conditions for plant growth. At a grassland restoration in Maryland, we studied the impacts of sequential prescribed burning on near-surface soil chemistry of a highly weathered soil. We hypothesized that soil pH and base cations in the surface soil would increase in the nutrient-poor soils after the burning from char hydrolysis and that cations would be retained in the surface soil between the burns. We collected soil cores 12 days and one year after a fall burn and 12 days after a subsequent spring burn. After the fall burn, we observed that soil pH, extractable cations, and organic matter (OM) were elevated in the soil profile in comparison to soil conditions before initiation of any burning, suggesting an impact of the dissolution of char (the mineral-containing carbonaceous residue of burning), increased root productivity since restoration, and leach­ ing of soluble constituents from aboveground litter in the case of soil K. One year after the second burn, only cations remained elevated. After the third burn, soil pH, OM, Ca, and Mg were greater in the depths below 10 cm in comparison to conditions prior to initiation of burning. We conclude that the net change over time in soil pH, extractable cations, and OM of grassland restorations in the first few years of prescribed burning will depend primarily on the input of new char, the presence of residual char, and the timing and magnitude of leaching events. As the grassland restoration ages, belowground productivity will likely contribute more significantly to changes in soil chemistry.