Wood ash as a fertilizer on drained mires — growth and foliar nutrients of Scots pine

The availability of phosphorus (P) and potassium (K) commonly limits tree growth on drained peatlands. The nutritional status and volume growth of Scots pine (Pinus sylvestris L.) after varying doses of wood ash fertilization were investigated in seven field experiments located on deep-peated sites in Finland between latitudes 63 degrees N and 67 degrees N. Needle samples were taken 14-20 years after fertilization and trees measured 15 years after fertilization. Annual growth rates and differences in foliar nutrients were analyzed with a two-way ANOVA model. A regression model was used in the analysis of periodic relative volume growth. High doses of wood ash (100-265 kg P(.)ha(-1), 225-450 kg K(.)ha(-1)) resulted in greater changes in foliar nutrient concentrations and in a stronger growth response than low doses (5-50 kg P(.)ha(-1), 14-210 kg K(.)ha(-1)). Significant increases in needle mass and concentrations of P, K, and B were observed in the ash-fertilized stands, with a good status for these elements 20 years after fertilization. Depending on the ash dose, the mean annual volume growth was 0.5-1.4 m(3.)ha(-1) higher than in the control plots during the 15 year postfertilization period.