Amelioration of magnesium deficiency in a Norway spruce stand (Picea abies) with calcined magnesite

Norway spruce has shown needle yellowing and defoliation symptoms on many s ites of the Bohemian Forest in north central Austria since the early 1980s. A forest amelioration experiment was set up to evaluate the response of sp ruce to magnesite based fertilizers with different solubilities. Response v ariables were a crown vigor index, diameter growth, nutrient contents in ne edles, soil solution chemistry, and soil chemistry. Soil solution at fertil ized plots showed an immediate response in base cation concentrations, nitr ate concentrations and pH-values. Fertilization increased the pool of excha ngeable cations in the upper 15 cm of the soil and reduced levels of exchan geable Al. The magnesium and calcium content of the needles of dominant tre es was greatly improved. Fertilization has increased the mineralization rat e of soil organic matter. Diameter growth, as a measure of tree vigor, show ed a pronounced positive response with a time delay of 5 years. Our results demonstrate that magnesite based fertilizers are a viable option to improv e the nutritional status of spruce forests on granitic bedrock.