Yield and energy balance of annual and perennial lignocellulosic crops for bio-refinery use: A 4-year field experiment in Belgium

- Energy use efficiency of crops with potential use in biorefinery chains was studied.
- Maize, timothy, and miscanthus achieved high DMY under the studied field conditions.
- Energy use efficiency was the highest for switchgrass and willow.
- Fertilizer application and starting material were major factors in the energy cost.
- Breeding should focus on resource efficiency and seed-based varieties.

In densely populated regions, such as, Belgium, value chains in the bio-economy can be organized on locally produced primary feedstock, allowing cutting down transport costs and reducing greenhouse gas emissions. The energy use efficiency of three major cropping systems under two fertilizer regimes was compared side by side in a 4-year field trial, with the farm-gate as system border. The annual crops maize, sorghum, and Italian ryegrass were compared with the grassland species perennial ryegrass, cocksfoot, timothy and tall fescue, and the lignocellulosic crops miscanthus, switchgrass, common reed, reed canary grass, and willow. Maize yielded as average a dry matter of 19.6 t ha−1 y−1 at medium fertilization level. The average dry matter yield of the other crops varied between 3 t ha−1 y−1 for common reed and 21.1 t ha−1 y−1 for Miscanthus × giganteus. However, the highest energy use efficiency was obtained for switchgrass and willow. The factors with the most important impact on the total energy input (EI) were fertilizer application, up to 79% for perennial ryegrass, and the preparation of starting material (e.g., up to 81% of the total EI is attributed to the production of miscanthus rhizomes). Targets for further improvement of the sustainability of the primary feedstock production are the development of resource efficient varieties, e.g., fertilizer use efficient maize varieties or seed-based miscanthus varieties, or the inclusion of energy efficient crops into the rotation system, such as energy beet instead of Italian ryegrass. This study provides interesting insight in the energy balances at the farm level for both the farmer and the industrial actors in the locally organized bio-refinery chains.