Production of biomass for energy in post-mining landscapes and nutrient dynamics

Since the German reunification in 1990 lignite production in the Lusatian mining region has significantly been decreased as a result of substantial economic and structural changes. This development coincides with efforts of the government of the state of Brandenburg to enhance the production of biomass for energy use on arable set-aside and post-mining land. In this context, the goal is to obtain a share of 3% of the primary energy consumption from biomass. As a part of the ongoing recultivation activities in the post-mining landscapes, short-rotation tree plantations as a special form of energy forests have recently come into focus. Thus, in 1995 a 2.5 ha short-rotation plantation was established on clayey–sandy, nutrient-poor substrates in the Lusatian mining area Welzow–Süd in order to study the yield potential of fast-growing tree species under the prevailing site conditions. Even under unfavourable soil conditions with a low N and P supply, above-ground biomass production after 4 years ranged from 5.3 to 19.6 tons dry matter (DM) per hectare. 4-year-old plants of fast-growing tree species like clones of poplar and willow and aspen progenies were marked by low mean N — ( 4.9 mgg−1 DM), Cl — (113 μgg−1 DM), Cd — (0.8 μgg−1 DM) and Pb — (0.5 μgg−1 DM) concentrations and a high ash softening temperature point of about 1680°C. For the biomass accumulated within this 4 year period, a calorific value of 42.000 MJha−1 a−1 has been calculated. The ash content of 2.4% allows this material to be used for amelioration purposes. This recycling approach guarantees balanced phosphorus, potassium, calcium and magnesium supply. To maintain adequate site productivity only for nitrogen a compensatory fertilization is required.