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Among energy crops, short-rotation coppices (SRC) are recommended to provide renewable energy. Compared to annual crops, willows and poplars are regarded as plants with low requirements for nutrients, herbicides, pesticides, and soil maintenance. However, only little is known about N-fertilizer effects on SRC and the few studies are even inconsistent. Therefore, we studied the effects of N on yields of willows and poplars in a field experiment. The effects of N fertilization on nitrate leaching and nitrous oxide emissions from the loamy-sand soil were also measured. Cuttings of willows (Salix viminalis clone Inger) and poplars (Populus maximovizcii × P. nigra clone max 4) were planted on farmland in 2008. The experiment was arranged in a random block design with three levels of N fertilizer (0, 50, and 75 kg N ha–1 y–1). After 2 y, the trees were harvested for the first time. Fertilization did not affect the yields of willows or poplars. However, the application of 75 kg N ha–1 y–1 caused an average increase of N leaching in the willow and poplar plots of 25 kg N ha–1 y–1 and 40 kg N ha–1 y–1, respectively. Emissions of N2O were increased by a maximum of only 0.2 kg N ha–1 y–1. Further, the N fertilizer stimulated the growth of the weed biomass in case of the willow plots by 46% and of the weed N content by 52% (r = 0.53). In conclusion, in the first 2 y, SRC could be produced in a more effective and environmentally friendly manner without mineral fertilizer.

Crops cultivated as feedstock for energy conversion processes (energy crops) could cover about 5% of the total energy demand of the European Union. Therefore, cultivation, harvest, processing, and finally utilisation of feedstock are required to be sustainable minimising environmental pressures and maximising environmental benefits. This contribution will give a comprehensive view on the environmental impacts of cultivating conventional energy crop species like cereals, rape seed and maize and of the hitherto uncommon species such as willow and poplar. Generalisations of environmental relevant parameters are deduced based on literature surveys as well as on results from own long-term experiments at Leibniz-Institut fur Agrartechnik institute. These parameters include biomass yield and energy yield, demand for water, fertiliser and pesticides as well as other environmentally relevant substances, emission of nitrous oxide and depletion and enrichment of soil carbon. In addition, recent results regarding ene...