Compensation of Nutrient Losses Resulting from the Intensified Use of Woody Biomass Using Bark-Ash Pellets

Given the increasing exploitation of low-diameter and low-quality woody biomass from forests for energy and industry purposes, the forest nutrient balance needs to be granted greater consideration. In order to return nutrients to the forest, bark-ash pellets (RIA pellets) were produced and spread on trial sites in the Oberlausitz and in north-eastern Bayern. The impact on soil chemical parameters and the nutrition status of the trees was monitored in the initial phase after the treatment. At the Oberlausitz sites, 2years after the RIA pellet treatment, a slow and moderate increase of the humus pH as well as a change in cation composition towards base cations was detected. The effect occurred slower and more moderately compared to a liming treatment. All effects were limited to the upper organic layer. At the trial site in Bayern, increased nutrient concentrations in the humus outflow were detected throughout the first 5years after the RIA pellet treatment. Nutrient concentrations in the seepage water at 40cm depth in the mineral soil horizon were not elevated compared to the control site, indicating that no loss of nutrients to the groundwater occurred due to the RIA pellet treatment. The slow nutrient release behaviour of the RIA pellets makes them an interesting option for returning nutrients to forest soils with a low sorption capacity. Under current economic conditions, it is not feasible to implement RIA pellets on a larger scale. This does not, however, reduce the relevance of the study, as with increasing energy prices, the costs might become acceptable in the future.