The growth productivity, and environmental impact of the cultivation of energy crops on sandy soil in Germany

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Energy plants, cultivated on set-aside land, could substitute nearly 3% of the primary energy in Germany and could raise the income of farmers. However, the substitution of fossil fuels by plants requires the selection of plant species with high site suitability, an ecologically benign farming system and high yields. This paper describes results of the cultivation of 10 energy plant species suitable for combustion. Over a period of 6 yr , yield, energy gain, and environmentally relevant substances in the plant and the soil were determined under practical conditions. Fertilization was carried out in four variants each ranging from 0 to 150 kg N ha −1 and with wood- and straw ashes, as well as basic mineral fertilizer. Plant protection products were entirely dispensed with. The results show that, except for topinambur haulm (Jerusalem artichoke) and short rotation coppice with undersown crops, the mean yield ranges between 8 and 12 t DM ha −1 and that a reduction of nitrogen application from 150 to 75 kg N ha −1 causes only slight yield losses. Without fertilization, yields diminish by 20–40% after 6 years , except for poplars, which reach similarly a high yield level as with fertilization. The contents of the emission- and combustion-relevant plant nutrients, such as nitrogen, potassium, sulfur and chlorine, are significantly lower in poplars and willows than in grass, rye, triticale and hemp. Heavy metals, such as cadmium, copper, zinc, and lead, are absorbed differently. Hemp, poplars, and winter rye allow high-energy yields to be achieved. Even if nitrogen fertilization is reduced, net energy gains of more than 120 GJ ha −1 yr −1 ( 3.2 kl oil equivalent ha −1 yr −1 ) are reached.