Effect of wood ash on soil chemistry of a pine stand in Northern Germany

Addition of wood ash to acid soils will affect the soil chemistry of forests in a number of ways which were assessed for a pine stand in northern Germany. A field experiment was carried out in a fifty-year old pine stand on a sandy Podzol at Fuhrberg (Luneburger Heide, Lower Saxony/Germany) which involved depositing wood ash (2.4 t ha(-1)) on the surface. Soil solution chemistry was investigated monthly at different depths for 24 months. Prior to and 19 months after the ash addition, exchangeable cations and amounts of heavy metals were determined at different depths. Two to four months after addition of wood ash, maximum mean concentrations in the soil solution of Ca were 240 mu mol l(-1) at 0 cm (surface of mineral soil) and 100 mu mol l(-1) at 100 cm and of K 980 mu mol l(-1) and 140 mu mol l(-1), respectively. The pH values in soil solutions dropped temporarily by 0.3 units at 0 and 10 cm depth. Nitrate concentrations increased at all depths and maximum mean concentration was 230 mu mol l(-1) at 100 cm. Concentrations of Pb and Cr in soil solution did not change significantly (p < 0.05) after ash addition. Concentrations of Cd and Zn increased significantly at some depths but stayed well below the legal limit for drinking water and below the limits given by the German recommendation for soil conservation. Nineteen months after ash addition, the cation exchange capacity (corrected for the release of cations from the ash) of the upper 6 cm of the organic layer was almost doubled and amounts of exchangeable Ca and Mg increased significantly in the upper 8 cm of the organic layer. Amounts of Zn were increased in the entire organic layer, but changes were significant only in the upper 4 cm. The results of is study suggest that ash from untreated wood (using modest additions) may be recommended for amelioration of forest soils.