| Land application of wood ash is gaining popularity as an alternative disposal method due to increasing landfilling costs. However, ash application increases soil pH and salinity and affects plant water and nutrient dynamics. This study determined the effects of high-volume wood ash application on (1) trace metal accumulation in soil and groundwater, (2) uptake of plant (slash pine) nutrients and trace metals, (3) the impact of changes in pH and electrical conductivity on the leachability of trace metals and (4) changes in physical properties in a forest soil. Ash application slightly increased soil metal concentrations, but groundwater metal concentrations increased substantially. Soil arsenic concentrations exceeded the United States Environmental Protection Agency (USEPA) Region 4 clean up goals and the groundwater concentrations of Se, Cr and Cd exceeded the National Primary Drinking Water Standard (NPDWS) for a few months before decreasing. The high pH (∼8.5) induced by ash application solubilized organic matter and increased metal leaching into groundwater. Acidification of the ash to pH 6–7 before application reduced the concentration of dissolved organic carbon (DOC) thereby decreasing metal leaching. Although the high pH mobilized large concentrations of DOC at our site, laboratory column studies using ash only showed that most of the fulvic acid fraction of DOC was retained in the matrix due to the high ionic strength. Fulvic acid metal reduced the leachability of some metals (e.g. Cu), but had very little effect on those elements that do not normally complex with organic matter. Total and plant available Ca, Mg, K, Cu, Mn, Fe and Zn increased substantially in the soil after addition of ash. Although plant uptake of trace metals was not enough to cause toxicities in slash pine (Pinus Elliottii, L), plant biomass was significantly reduced due to nutrient uptake problems caused by the salinity and high pH. Ash application at this site also increased soil water holding capacity and reduced hydraulic conductivity due to its fine texture, but the added salinity may have neutralized this potential benefit by increasing the plant energy requirement for water uptake. Wood ash application should be done conservatively, based on the liming and nutrient requirements of the soil, in order for it to be sustainable. |
