Environmental impact of grass-based cattle farms: A life cycle assessment of nature-based diversification scenarios

Abstract

Diversification is widely considered to positively influence the environmental sustainability of livestock farming. Multiple options exist to diversify cattle farms, but few have been examined at a systems level for grass-based livestock farms. Three nature-based diversification options recommended for livestock farms were examined in this study: mixed grass–white clover swards (GWC), organic farming (OFS) and agroforestry (AGF). They were applied on dairy and suckler calf-to-beef farming systems common in the Republic of Ireland. Both of these bovine systems were evaluated over a 3-year period (2017–2019) and were nationally representative. The environmental impact and resource use of dairy and suckler calf-to-beef systems were modelled using life cycle assessment (LCA). The system boundary of the LCA model extended from the extraction of raw materials to the sale of milk and cattle from the farm, i.e. cradle to farm-gate. Six of the major environmental impacts of cattle farming were simulated; global warming potential (GWP), non-renewable energy (NRE) depletion, land occupation (LO), acidification potential (ACP), freshwater and marine eutrophication potential (FEP and MEP). Impacts were scaled to the following functional units: land area, fat and protein corrected milk (FPCM) for dairy and carcass weight (CW) for beef. The result illustrated that GWC swards reduced the GWP of milk production by 9% and cut the GWP of beef LW by 3%. Per unit of product, this strategy decreased ACP by 4%–5%, NRE depletion by 13%–19% and LO by 6%–7%. However, it increased MEP by 5%–12% due to clover fixing more N than it replaced. Cattle farms based on GWC were more productive than conventional farms, but tended to increase impacts per hectare. Organic farming had the lowest environmental impacts per unit of land and reduced GWP and NRE depletion. Without carbon sequestration, organic farming had the opposite effect on GWP of FPCM and increased ACP and MEP per product unit. Declines in productivity in organic systems led to the rise in these impacts per unit of product and increases in LO relative to conventional systems. Partial conversion (10%–20%) of grassland to silvopasture decreased milk and beef output, and slightly improved environmental performance. Carbon sequestration was greater in silvopasture than in grassland, albeit LCA models struggle to accurately quantify the influence of management change on this process. This issue can be overcome through more field and modelling research on sequestration. Further research is also required on combining diversification options to optimise the environmental sustainability of cattle farming.