Changes in cropping systems associated with biogas plants in French cereal-growing areas

CONTEXT

Anaerobic digestion (AD) is a process that produces a renewable gas (biogas) and an organic fertilizer (digestate). Energy cover crops, grown between two main crops, are expected to become the predominant AD feedstock in France and other European countries, potentially reshaping cropping systems and agricultural practices. However, farming systems linked to AD remain understudied, potentially leading to AD assessments disconnected from actual farming practices.

OBJECTIVE

Our aim was to address this gap by characterizing the cropping system changes in French farms associated with biogas plants mainly relying on energy cover crops in cereal-growing regions and to discuss the differences with agricultural practices usually considered in AD assessments.

METHODS

We conducted interviews on 33 farms in French cereal-growing regions between late 2020 and 2023 to characterize changes in cropping systems of non-livestock farms associated with AD. The interview guide covered general farm and biogas plant information, main crop and energy cover crop management, farm-scale fertilization and digestate management. Land cover changes before and after AD were considered, as well as the calculation of a simplified farm-scale nutrient (N, P and K) balance.

RESULTS AND CONCLUSIONS

Key findings revealed that energy cover crops were grown on an average of 30 % of farm surfaces each year. They were generally treated with pesticides, and irrigated on half of the surveyed farms when cultivated in summer. Their introduction implied significant reductions in surfaces of crops with longer growing periods, such as wheat and rapeseed, while the surface of barley, maize and other cereal crops increased. Yield losses of −10 % to −40 % in main crops following winter energy cover crops were reported by 39 % of respondents, who mainly attributed them to delayed sowing dates of summer crops, resulting in a shorter growth period. Potential fertilizer savings achievable through digestate application varied across farms and were positively correlated with the proportion of agro-industrial byproducts in the digester.

SIGNIFICANCE

This study provides the first description of agricultural practices of non-livestock farms with AD based mainly on energy cover crops in cereal-growing regions. It highlights discrepancies between observed practices and those considered in AD assessments. Future local or national assessments of AD should account for actual on-farm practices, evaluating the impacts of climate change and the potential water scarcity on cropping systems with AD. This is necessary to mitigate any adverse effects resulting from the energy transition.