Leaching of wood ash and lime products: Laboratory study

Deposition of acidifying compounds (sulphur and nitrogen) in combination wi th the harvest of forest biomass leads to diminished amounts of exchangeabl e base cations and micronutrients in soil. A larger loss of base cations th an is supplied by weathering and deposition leads to diminished product:ion capacity of the soil. This might be compensated by the spreading of wood a sh, thereby returning mineral nutrients to forest soils. The purpose of thi s study was to illuminate variation between different wood ashes with respe ct to acid neutralizing capacity (ANC), base cations and mineral nutrient s olubility. This has been done as a laboratory leach study. Leaching was car ried out by mixing wood ash and distilled water adjusted to pH 4.0 (ratio 1 :2000). Leachate was poured off after 24 h and new solution added. Leachat e was analysed. This procedure, with daily change of solution, continued fo r 30 days. Concerning ANC, tested ash products were more reactive during sh ort time tests than lime products. Rates of leaching varied between differe nt substances in the ashes. Mean values for totally leached amounts from as hes were 79%, 53%, 27%, 22%, and 48% for Ca, Mg, Mn, Al and P, respectively . Particle size was less important for ANC and leached amounts from ashes c ompared to that for lime products.