Profitability analysis of cropping systems for biogas production on marginal sites in southwestern Germany

Abstract

Power based on biomass, in particular biogas, is increasing, with a concomitant increase in the need for energy crop production. The objective of this study was to determine the profitability of biogas substrate production on a marginal site in southwestern Germany. The effects of crop rotation and nitrogen fertilization level were evaluated in a three-year filed experiment. Production costs for supply of biogas substrates and sales of produced electricity were assessed using five crop rotations (CR1: annual monoculture maize; CR2: perennial monoculture perennial ryegrass; CR3: perennial monoculture Jerusalem artichoke; CR4: three-course crop rotation of sorghum – winter triticale – clover grass; CR5: four-course crop rotation of catch crop – maize – winter wheat – winter triticale) and three nitrogen fertilization levels (zero, middle and high levels of nitrogen). The variables were production costs, dry matter yield, substrate costs, energy output, biomass energy supply price, biomass energy sales price and sale/supply ratio. Production costs increased in the order CR4 (1252 € ha−1 a−1) < CR2 (1256 € ha−1 a−1) < CR5 (1404 € ha−1 a−1) < CR3 (1462 € ha−1 a−1) < CR1 (1649 € ha−1 a−1) due to differing mechanical cultivation needs. Dry matter yields ranged from 10.8 t ha−1 a−1 (CR3) to 4.0 t ha−1 a−1 (CR2) and showed significantly higher yields with increasing fertilization levels. Accounting for all variables, the lowest biomass energy supply price was achieved with CR3 (6.6 ct kWh−1), and increased in the order CR1 < CR5 < CR4 < CR2 (12.4 ct kWh−1). It was determined that only CR3 and CR1 were effective for the production of biogas substrates on marginal sites. The biogas substrate costs of the remaining crop rotations were not compensated for by the sale of electricity.