Liming acid forest soils with flue gas desulfurization by-product: growth of Northern red oak and leachate water quality

Flue gas desulfurization (FGD) by-product is created when a dolomitic lime [CaMg(CO3)2] is used to remove SO2 during the burning of high sulfur coal in electricity generating power plants. This study evaluated growth of Northern red oak (Quercus rubra L.) in an acid forest soil (Rayne silt loam—a fine loamy, mixed, mesic, Typic Hapludult) and water leachate quality when FGD by-product was applied topically or mixed within the A horizon at rates equivalent to 0.25, 0.50, 1.0, 1.5, 2.0 and 2.5 times the soil’s lime requirement. Soils were leached with deionized water on a monthly basis and the leachate samples were analyzed for pH, conductivity, P, S, B and metals (Al, Ca, Cr, Cu, Fe, Mn, K, Mg, Pb, Ti and Zn). Tree growth significantly increased (p 0.05) when soil was treated with FGD and the greatest growth (75% increase over the untreated control) occurred when FGD was applied at 1.5 times the lime requirement rate. Boron toxicity symptoms were observed in plant tissue when FGD by-product was applied at two times (or higher) the lime requirement rate. Sulfur concentration increased from less than 10 mg l−1 (control soil) to 234 mg l−1 (soil treated with FGD at 2.5 times the lime requirement) in the leachate four months after treatment. Boron also approached toxicity concentrations (≈l mg l−1) in the leachate from soil treated at the highest rate during the initial leachings, but concentrations tended to decline with time. Applying FGD by-product onto acid forest soils has the potential to provide growth benefit to a commercially important tree species (red oak) but care will need to be taken to avoid using FGD materials that may release toxic levels of B.