Implementation and soil ecological characterization of short rotation coppices and agroforestry systems in the bioenergy regions "district of Göttingen" and "Thuringian cropping Area"

In the context of climate change and the decrease of fossil fuels the production of renewable energies should be extended. The use of biomass is one option to help secure the energy supply. Based on the need for regional increase of biomass production for material and energetic use the research framework BEST - for the support of bioenergy regions - is being conducted since 2010. One focus of BEST is set on the development of regionally adapted concepts and innovative systems for the production of woody biomass taking into account ecological and economic effects. Research activities of BEST were linked to two bioenergy regions: the district of Göttingen (Ldk. Gö.) located in Southern Saxony and the initiative "BERTA" (BioEnergy Region Thuringian cropping Area) in the center of the Thuringian cropping area. The subproject "Agroforestry and short rotation coppices" of BEST as the base of this study analyses innovative systems for the production of woody biomass. Main goals of the study are: (i) the development of regionally adapted concepts and innovative systems for the production of woody biomass within the land use systems short rotation coppice (SRC) and agroforestry (AF). SRC provide woody biomass with fast growing trees, like poplar or willow, on agricultural land. The combination of SRC rows and grassland or arable crops on the same agricultural site are called AF. (ii) Establishment of practical SRC and AF study sites in both bioenergy regions Ldk. Gö. and BERTA. (iii) Soil ecological characterization of the study sites. (iv) Deduction of practical recommendations. Furthermore, the following subgoals were identified for achieving the main goals: (i) provision, analysis and assessment of geological, climatic, soil physical and soil chemical data for the study sites in both bioenergy regions, (ii) analysis of the nutritional status of the fast growing trees, (iii) verification of success by gathering information on growth and yield, (iv) measurement and comparison of litter production, litter loss and nutrient release for the used clones, (v) estimation of fluxes and pools of initial nitrogen cycling, (vi) integrated assessment of suitability for the study sites concering KUP and AF. Several disciplines (meteorology, soil science, geology, geography), data (long term data from the German Weather Service) and observations (detailed soil mapping, soil profiles, leaf nutrient content, buried bags, deposition) were used for evaluation of the study sites with fast growing trees (poplar clone "Max 1" and willow clone "Tordis"). For characterization of water supply climatic and soil physical data were used. Based on the results of the long term mean precipitation and the available water capacity of soil an establishment of SRC and AF in BERTA cannot be recommended. However, the planting of SRC and AF can fully be recommended in Ldk. Gö. Geological and soil chemical data indicate good nutrient conditions for plant growth of poplar and willow. However, low initial biomass yields, with a maximum of 3.2 tatro ha-1 a-1 were calculated for both study sites with the help of allometric power equations. Survival rates and initial biomass yields were higher by poplar in comparison to willow. Especially the survival rates of willow (approx. 90 %) were higher than for poplar (maximum of 74 %). Further litter production, decomposition and nutrient release was higher for poplar clone "Max 1" in comparison to willow clone "Tordis". Therefore, more nutrients are returned with poplar litter into the soil in comparison to willow. Initial nitrogen (N) cycling, fluxes and pools of N and N use efficiency were analyzed for SRC and AF in both regions. Fluxes of mean Net-N-Mineralization (NNM) plus the measured atmospheric N bulk deposition were taken as the input terms. Using buried bags for NNM, no significant differences between SRC, AF and agricultural control plot were detected. Atmospheric N deposition was very similar for both regions (11 - 13 kg (N) ha -1 a-1). Output terms for N were defined as the plant uptake in wood, including bark, plus the losses of N by nitrate leaching and N2O emissions. High nitrate leaching was especially determined immediately after establishment of SRC and AF but decreased towards the end of the observation period. Highest nitrate leaching was observed for willow in SRC on both study sites. Plant uptake of N in wood, including bark was highest in poplar SRC, mainly caused by higher nutrient contents and biomass yields in comparison to willow. N2O emissions for poplar SRC were determined up to a maximum of 2 kg ha-1 a-1 in both regions. Initial N-budgets for all plots (considering the input and output fluxes) ranged between -14.7 kg (N) ha-1 a-1 and 22.5 kg (N) ha-1 a-1 for SRC and AF. In Ldk. Gö., SRC and AF always showed positive N-budgets whereas in BERTA, negative N-budgets were calculated for SRC with willow and SRC with poplar. A positive N-budget indicates an accumulation of N despite of nitrate leaching, N-uptake in wood and N2O emissions. Willow seems to be more efficient than poplar with respect to N use efficiency. A higher biomass production was observed for willow in comparison to poplar considering the same amount of nitrogen, which means willow is more effective in the use of nitrogen. Considering low stock of nitrogen in soil, willow is the most N-efficient system to produce woody biomass. Poplar should be used if the main goal is diminishing N eutrophication and yielding high woody biomass. The study site in Ldk. Gö. can be recommended for the establishment of KUP and AF considering natural characteristics and N-balance