Effects of a second wood ash application to soil on Picea mariana (Mill.) B.S.P. and Picea glauca (Moench) voss growth and foliar nutrition and soil chemistry
As the Canadian biomass energy sector grows, so too does its production of by-products such as wood ash from the combustion of wood biomass for energy. Wood ash can be land applied with the goal of increasing the productivity of a site through an increase in soil pH and available nutrients. Most studies have focused on a single ash application to the soil. The purpose of this study is to investigate the effects of re-applying wood ash on the chemistry of a forest soil and the growth and foliar nutrition of two commercially important tree species (Picea mariana (Mill.) B.S.P. and Picea glauca (Moench) Voss). A low and high carbon wood ash sourced from vibrating power boilers at the Resolute Forest Products facility in Thunder Bay were re-applied in 2019 to plots established in 2012 at the Ministry of Natural Resources, Northwest Science and Technology Center, 25th Side Road. The wood ashes were applied at 0, 1000, and 10 000 kg ha-1 alone and in combination in 5 replicate blocks. Tree height and diameter were measured in the Fall of 2019 and 2020 and soil and foliar samples were collected at the same time for chemical analyses. A second application significantly affected concentrations of soil C, C:N, conductivity, pH, total soil Ca, S, Sr, and exchangeable Ca, K, Mg, Na, and extractable Cu, Mn, and Zn concentrations. Differences attributable to species were observed for soil C concentrations, conductivity and exchangeable K concentrations. Concentrations of soil C, conductivity, exchangeable K and extractable Zn differed between years. Three trends were observed in soil chemistry: 1) low C ash had a greater effect on measured parameters than the high C ash, 2) applying ash at higher rates had a greater effect, and 3) applying low C ash in addition to high C ash had greater impact on soil than when high C ash was applied alone. Foliar and growth response from wood ash re-application were species dependant. Picea marianna (black spruce) showed a negative foliar Mn response and a non-significant but negative height growth response to ash where Picea glauca (white spruce) did not show any effect of ash application. Lower foliar Al and black spruce foliar Mn were observed when higher amounts of ash were applied and when low C ash was applied. Foliar S responded to ash application after the first growing season and low C ash had the greatest effect. Comparing these results to the first ash application in 2012: 1) high C ash had a greater impact on soil chemistry after the second ash application, 2) the concentration of some soil metals (extractable Cu, Zn, and Mn, and total Sr and Ca) increased with the second application, though not to toxic concentrations. This study shows that a repeat ash application to soils can increase concentrations of Ca, K, Mg, and S in soil, reduce the impact of soil acidification, and combat soil C depletion that follows whole tree harvesting, at least in the short term, while having no significant immediate negative effects on black and white spruce growth and foliar nutrition.