A Preliminary Study on Producing Volatile Fatty Acids from Winter Cover Crops

Winter cover crops provide many ecological benefits, though their economic impacts have been shown to be mixed. While cover crop biomass is typically terminated or used as livestock feed, it can also serve as a feedstock for bioenergy production, offering opportunities for additional revenue. This study evaluated the potential of wild pennycress, CoverCress™, annual ryegrass, cereal rye, and field pea biomass for volatile fatty acids (VFAs) production through arrested anaerobic digestion (AAD). Specifically, the effects of harvest timing on cover crop biomass composition and VFAs yield were examined, given the need for effective utilization and storage of early-harvested biomass. The five cover crops were planted in fall 2023 following soybeans and harvested at three different times in 2024. Batch AAD experiments were conducted with a methanogenesis inhibitor added. Results showed that harvest timing significantly affected biomass yield, composition, and VFAs production. Protein content decreased whereas lignin content increased as the crops matured. Total VFA yields ranged from 0.08 to 0.30 g/g-VS (volatile solids), with acetic, butyric, and propionic acids as the main components. The early-harvested cover crops produced similar or higher VFA yields, indicating that AAD is a suitable technology for these feedstocks. Estimated revenues from the produced VFAs were substantial, demonstrating the potential of winter cover crops as feedstocks for VFAs production. Evaluated volatile fatty acids (VFAs) yields from biomass of five cover crops. Harvest timing significantly affected cover crop biomass composition and VFAs yield. Total VFAs yields were in the range of 0.08–0.30 g/g-VS from cover crop biomass. Early-harvested cover crop biomass is suitable for VFAs production. Revenue from cover crop–derived VFAs can be substantial.