Regional and site-related patterns of soil nitrogen, phosphorus, and potassium stocks and Norway spruce nutrition in mountain forests of the Bavarian Alps

For the mountain forests of the Alps, limited comprehensive information is available about soil stocks of important nutrients (N, P, K), stand nutrition, and relationships between soil status and stand nutrition. We investigated total and plant-available soil N, P, and K stocks and the nutritional status of Picea abies concerning these elements on 14 forest soil monitoring sites in the Bavarian Alps. Mean soil N, P, and K stocks are 8.0 Mg N ha(-1), thereof 14 % bound in the forest floor, 1.7 Mg P ha (-1) (2 % in forest floor), and 42 Mg K ha(-1) (0.2 % in forest floor). Citric acid-extractable orthophosphate and exchangeable K contribute to 3 and 0.7 % of total P and K, respectively. Spruce N, P, K, and Mn nutrition differs considerably among sites, with Rendzic Lithosols being most critical, whereas trees on deeply weathered soils are well supplied. According to our estimation, the forest is characterized by an insufficient supply with N, P, and/or K at about 30, 20 and 10 % of the forest area in the Bavarian Alps, respectively. A large part of the Bavarian Alps can be judged critical and prone to nutrient shortage in the course of humus degradation and associated SOM losses.