The feasibility of using marginal hay meadow biomass for anaerobic digestion

Marginal (‘upland’) areas in the UK are enjoyed by many tourists, and provide ecosystem services of clean water, soil carbon storage and agricultural produce (breeding livestock, meat and wool). However, poor financial return from the agricultural land puts it at risk of abandonment. Hay meadows in marginal areas are prized for their biodiversity, which is maintained by their traditional, low-input management including sheep production. If their management was abandoned, their biodiversity would fall. This thesis examined if bioenergy production (by anaerobic digestion (AD)) could provide a sufficiently high income compared to sheep farming, to prevent total abandonment. In addition to encouraging biodiversity, this could mitigate climate change by reducing fertiliser input and producing renewable energy. In marginal areas in northern England, fresh vegetation from five hay fields (not receiving inorganic fertiliser) was compared to five silage fields (receiving inorganic fertiliser), because grass silage is commonly used in AD. Biodiversity; biomass yield; biomethane production by laboratory AD; greenhouse gas (GHG) emissions; and financial returns from sheep farming or using the silage/hay crop in AD were measured. Compared to silage fields, the hay fields had greater biodiversity, lower GHG emissions but similar biomethane production. And hay was more financially viable in AD than silage, partly due to lower cost. However, in order to make a similar profit per ha to that achieved by sheep production, a farmer would have to sell their hay to a nearby AD plant (such as a dairy farm AD), rather than form a co-operative AD. Bioenergy is commonly perceived as an ‘enemy’ of biodiversity, but my work shows that bioenergy and biodiversity could co-exist, through AD of hay.