Soil-solution chemistry in a coniferous stand after adding wood ash and nitrogen

Wood-ash applications have been proposed to promote the long-term sustainability of forest production at increased harvest intensities. Effects of wood-ash and nitrogen (N) application on soil-solution chemistry were studied for 9 years following application in a coniferous stand in Sweden. Crushed, self-hardened wood ash was applied at 3, 6, and 9 Mg·ha–1 alone, the lowest dosage both with and without 150 kg N·ha–1. Pelleted wood ash (3 Mg·ha–1) and N were also applied alone. The soil solution was sampled by suction cups at 50 cm depth. The crushed, self-hardened ash readily dissolved in water, as reflected in increased soil-solution concentrations of sodium and sulphate. Significant (p < 0.05) elevations were also found for potassium, calcium, aluminum, and total organic carbon. Vanadium, chromium, manganese, nickel, copper, zinc, arsenic, and lead were not significantly affected by the ash treatments, but cadmium tended to increase in the treatments with ash alone. From the fourth year onwards, the pH of the soil solution was lowered and the aluminum concentration raised in the plots given 9 Mg crushed ash·ha–1. Fertilization with N alone temporarily increased concentrations of inorganic N, cadmium, aluminum, and zinc and decreased the pH. The crushed ash generally had longer lasting effects than N fertilization.