Long terms effects of the application of bark-ash-pellets on seepage water, soil chemistry and nutrient development in an old growth spruce forest

The rising demand for biomass with increasing use of small sized wood for energy purposes asks for a nutrient sustainable management. In this study long term application effects of bark-ash-pellets were investigated in a spruce stand in north-east Bavaria (Tab. 1). The bark-ash-pellets are an attempt to bring back the nutrients contained in wood ashes into forest stands while negative properties of untreated ashes are being minimized. The bark-ash-pellets are a multiple nutrient fertilizer with high contents of Ca, Mg, K and also P (Tab. 2). Calcium was chosen as an index element to compare the application of bark-ash-pellets (60% bark, 40% wood ash) with a typical liming of 3 t ha-1. Thus, the application of these pellets was 4.31 t ha-1 (Tab. 1). To analyze the effects on changes in nutrient concentrations water samples collected below the humus layer and seepage water in the depth of 40 cm were taken for six years. Also the changes of cation exchange capacity (humus layer, mineral soil in depths of 0-5 cm, 5-10 cm, 10-20 cm, 20-40 cm), nutrient content of the humus layer and the development of the pH-value in the humus layer and soil were investigated. Three years after application, done in August 2008, the pH-value of the outflow in humus lysimeter (Fig. 1) and the concentrations of Ca (Fig. 2), Mg (Fig. 3) and K (Fig. 4) increased significantly. In seepage water for pH and Ca only in the years of 2011 and 2013 differences were observed (Fig. 1+2). In the case of Mg the differences between both variants were statistically different since 2010, but concentration differences were on low level (Fig. 3). At the end of the observation period a higher concentration of nitrate were measured below the humus layer, but not in 40 cm depth (Fig. 5). After the application of bark-ash-pellets the BaCl2-exchangeable cations of Ca, Mg and Mn increased in the humus layer (Tab. 3). Changes in mineral soil properties (cec) were marginal (Tab. 3). The application increased the nutrient contents of Ca, Mg, Mn and K in the humus (Tab. 4). The nutritional state of the spruce stand significantly improved for Ca, Mg and P (Fig. 10). The bark-ash-pellets are an ecosystem compatible way for the recycling of nutrients exported by using fire wood. At the investigated site there were only minimal nutrient losses with seepage water, so that nearly all nutrients applied by bark-ash-pellets were kept in the system.