Reduction of greenhouse gas emissions by wood ash application to a Picea abies (L.) Karst. forest on a drained organic soil

Wood ash additions of 3.3 and 6.6 t ha(-1) reduced greenhouse gas (GHG) emissions from a spruce forest (Picea abies) on a minerotrophic drained organic soil. Emissions of carbon dioxide (CO2), methane (CH4) and nitrous oxide (N2O) were measured using static dark chambers for two years following the ash treatment. The CO2 emission from the soil was significantly reduced by 17-23% by both doses during 2006-2008. The mechanism behind the reduction could not be related to a direct inhibition of soil C mineralization by the ash. The emission of N2O was also significantly reduced by 44 and 46% during the first year, mainly due to reductions in the winter emissions. Similar reductions of 34 and 50% were found in the second year for the low and the high wood ash, respectively. Increased pH of the soil due to the ash additions may have caused the effect. The control and amended soils consumed ambient CH4. The low wood ash dose increased the annual net CH4 uptake rate by 9%, due to an increased winter uptake. No changes in tree growth could be detected over the short 2-year measurement period. The net effect of wood ash application was a reduction in the total GHG emissions during the first two years after the treatment.