2.2. Life cycle inventory(LCI) analysis

All foreground data were sourced from the UK Research and Innovation National Bioscience Research Infrastructure, the North Wyke Farm Platform (NWFP). Despite having a range of long-term system trials on the NWFP, for the purposes of this study, the permanent pasture system (50°46′10″N, 3°54′05″W) was deemed sufficient to elucidate the research goal detailed in section 2.1 (figure ​(figure1).1). The NWFP is one of the most instrumented farms in the world for assessing the environmental performance of farming systems (Orr et al 2016, Takahashi et al 2018). The data utilised in the current study covered the 2016 permanent pasture cattle grazing system, meaning animals for finishing were born in 2015, grazed in spring and summer of 2016, and typically finished towards the end of 2016 (table ​(table1).1). The finishing farm occupies approximately 21 ha, and in 2016 the beef enterprise maintained 30 Charolais × Hereford–Friesian finishing cattle sourced from an adjacent suckler herd farm which is managed in the same manner as the NWFP permanent pasture system (e.g. fertiliser rates, stocking densities etc; tables ​tables22 and ​and3).3). All GHG emissions for 2016 were calculated according to McAuliffe et al (2018) using a modified IPCC (2006) Tier 2 approach, which aligns with the majority of extant grassland LCA literature.

Livestock performance of finishing cattle grazing the permanent pasture system on the NWFP.

Suckler herd structure and performance.

Material inputs to the system and measured pasture quality for the 2016 grazing season. All values were recorded by farm staff throughout the production cycle.

A large-scale sensitivity analysis capturing emission factor uncertainties was developed to assess the effect of climate impact interpretation of a typical lowland grazing beef system whilst also capturing coefficient uncertainties (i.e. Y _m, EF₁ and EF₃) which fall within the range of latest IPCC guidelines (IPCC 2019). As the permanent pasture system also supports sheep (75 ewes plus their offspring: typically twins), on-farm impacts of sheep grazing, both positive through lamb production and associated soil fertility via excreta deposition as well as negative through GHG emissions, were separated from the model using the economic allocation-based decomposition method outlined in McAuliffe et al (2018). Material inputs to the system are displayed in table ​table3.3. Emissions associated with background processes, such as field activities and the production of small quantities of supplementary feeds (rapeseed expeller in the current case), were sourced from the life cycle databases ecoinvent (Wernet et al 2016) and Agri-footprint (Blonk et al 2022). Embedded CO₂ emissions (e.g. energy consumed, fertiliser production, transportation, etc) were calculated using the aforementioned LCA databases. A 9 × 10 full factorial virtual experiment was designed to include various combinations of CH₄ (Y _m range = 4.5%–8.5%, in steps of 0.5%, with 6.5% being the default) and N₂O (EF₁ range = 0.2%–2.0%, in steps of 0.2%, with 1% being default, + EF_3PRP range = 0.4%–4.0%, in steps of 0.4% with 2% being default) emission factors. These stepwise changes were adopted to test decision-making surrounding EFs mathematically, but it is important to reiterate that our calculations remain within IPCC’s novel recommended uncertainty ranges (i.e. 95% confidence intervals), particularly given the new system-specific seasonally- and feed-driven tailored CH₄-yield (MY; kg CH₄ per kg dry matter intake; DMI) calculations available from IPCC (2019).