Improving the energy balance of bioethanol production from winter cereals: the effect of crop production intensity

Abstract

Energy balances were calculated on the basis of biennial field trials conducted at two locations in southwest Germany. Winter cereals (rye cultivar ‘Farino’, triticale cv. ‘Modus’, wheat cv. ‘Batis') were grown under different crop production conditions (and intensities) optimized for ethanol production. To minimize the use of fossil energy, previous legume crops (pea, grass–clover) or stillage were substituted for mineral nitrogen. Stillage is a liquid processing residue from bioethanol processing that contains nitrogen in organic form. Along with the grain, straw, and bioethanol yields per hectare, both the cultivation and conversion processes were considered. The net energy gains (GJ ha −1) and output/input ratios were computed either with or without by-product stillage and straw. As crop production intensity increased, both the energy output and the net energy gain per ha rose. However, the output/input ratios fell. Peak net energy gains (max. 56.4 GJ ha −1) and highest output/input ratios (max. 3.07) without by-product consideration occurred after a previous pea crop. In stillage manuring, the net energy gains remained minor in comparison to mineral nitrogen fertilization because of poor cereal yield. Hence, the entire replacement of mineral nitrogen with stillage could not be approved unreservedly. Replacing basic nutrients (i.e. P 2O 5, K 2O) appears more feasible instead.