Silage maize and sugar beet for biogas production in crop rotations and continuous cultivation - energy efficiency and land demand

Empirical data on energy performance (net-energy yield, energy efficiency, land demand) of biomass crop cultivation are needed for policy and agronomic decision making. Energy input and energy performance of the cultivation of silage maize (SM), sugar beet (SB), and winter wheat (WW) in crop rotations and continuous cultivation were evaluated on the basis of three field experiments on highly productive sites in Germany. Silage maize and SB root were considered as crops for biogas production and WW as a food crop. Even if SM cultivation needed the largest energy input across sites and years (19-22 GJ ha−1 a−1), the energy output compensated for it and largest net-energy yield (212-317 GJ ha−1 a−1), energy efficiency (11.4-17.1 GJ GJ−1), and smallest land demand (33-48 m2 GJ−1) were observed. For SB cultivation, energy input (15-19 GJ ha−1 a−1) and energy performance were lower (119-266 GJ ha−1 a−1, 9.1-14.7 GJ GJ−1, 38-279 m2 GJ−1, respectively). Differences between both crops were significant (p ≤ 0.05), but not in all cases. Winter wheat cultivation required an energy input of 13-18 GJ ha−1 a−1 and showed the lowest energy performance (103-119 GJ ha−1 a−1, 6.6-8.6 GJ GJ−1, 84-102 m2 GJ−1, respectively). The net-energy yield and land demand values presented are among the largest and the lowest, respectively, for rainfed Central European conditions. As the preceding crops, SB induced a higher energy performance of the subsequent WW than SM. When taking such crop rotation effects into account for the overall evaluation, we concluded that SB root as a biomass crop is a suitable alternative to SM.