Conditions for efficient alkaline storage of cover crops for biomethane production

[Display omitted] •Alkaline storage was used on rye and sunflower cover crops in wet and dry conditions.•The abiotic transformations that occur during the very first hours were investigated.•Stable and unstable alkaline storage were obtained depending on TS content.•Microbial fermentation was able to restart after three weeks at pH 12.•The methane potential of the crops were increased in the stable alkaline condition. An innovative process aiming to combine storage and alkali pretreatment of cover crops was investigated using lime as a low cost and environmental friendly reactant. Different lime loadings and Total Solid concentrations (TS) allowed to highlight the abiotic mechanisms of deacetylation during the early stages of the process. Long-term storage experiments of rye and sunflower cover crops at 100 g.kgTS−1 lime loading allowed to evaluate the fermentation kinetics and to compare performances in dry and wet conditions to classical silage storage. The dry condition allowed an efficient alkaline storage and up to a 15.7% Biochemical Methane Potential (BMP) increase, while the wet condition underwent a succession of fermentations with a high butyric acid accumulation and H2 production, leading to a 13% BMP loss. Silage experiments allowed an efficient preservation of the BMP, with no significant variation over the 6-month storage duration.