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

Energy balances were calculated on the basis of biennial held trials conduc ted at two locations in southwest Germany. Winter cereals (rye cultivar 'Fa rino', triticale cv. 'Modus', wheat cv. 'Batis') were grown under different crop production conditions (and intensities) optimized for ethanol product ion. To minimize the use of Fossil energy, previous legume crops (pea, gras s-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 he ctare, both the cultivation and conversion processes were considered. The n et energy gains (GJ ha(-1)) and output/input ratios were computed either wi th or without by-product stillage and straw. As crop production intensity i ncreased, both the energy output and the net energy gain per ha rose. Howev er, 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 considera tion occurred after a previous pea crop. In stillage manuring, the net ener gy gains remained minor in comparison to mineral nitrogen fertilization bec ause of poor cereal yield. Hence, the entire replacement of mineral nitroge n with stillage could not be approved unreservedly. Replacing basic nutrien ts (i.e. P2O5, K2O) appears more feasible instead. (C) 2000 Elsevier Scienc e Ltd. All rights reserved.