Effects of Wood Ash Application on Tree Nutrition and Soil Dynamics in a Pinus taeda System

Many Brazilian forest industries use wood biomass as a sustainable energy source that generates a wood ash by-product. This residue is typically discarded in nearby planted forests. To evaluate the effects of wood ash rates on Pinus taeda L. growth, a study was established on a high clay soil in 2006. Five rates of wood ash (0, 10, 20, 40, and 80 T ha(-1)) were applied to a P. taeda system. Soil chemical properties were evaluated three times at different depths. Tree growth (i.e., height, diameter at breast height, and commercial volume) and nutrition (needle elemental composition) were determined. After 11 years, litter accumulation and soil mobilization (bioturbation) were also evaluated. Ash application did not affect tree growth/yield or litter accumulation. A small reduction in soil acidity and increased bases in the upper soil layer were observed two years after ash application; this effect reached deeper layers after six years but retreated to shallower depths at 11 years. A soil amount of 14.6 m(3) ha(-1) year(-1) was relocated closer to the soil surface due to bioturbation by edaphic fauna. The application of wood ash to forest soils appears to be an ecologically sound alternative for disposal of this industrial by-product. Study Implications: Wood ash residue is an environmental liability that requires adequate disposal. Our study showed that even high amounts of this residue (80 T ha(-1)) can be safely applied to a planted forest system, reducing the costs when compared with disposing the residue in landfills.