Evaluation of the effect of accounting method, IPCC v. LCA, on grass-based and confinement dairy systems’ greenhouse gas emissions

Abstract

Life cycle assessment (LCA) and the Intergovernmental Panel on Climate Change (IPCC) guideline methodology, which are the principal greenhouse gas (GHG) quantification methods, were evaluated in this study using a dairy farm GHG model. The model was applied to estimate GHG emissions from two contrasting dairy systems: a seasonal calving pasture-based dairy farm and a total confinement dairy system. Data used to quantify emissions from these systems originated from a research study carried out over a 1-year period in Ireland. The genetic merit of cows modelled was similar for both systems. Total mixed ration was fed in the Confinement system, whereas grazed grass was mainly fed in the grass-based system. GHG emissions from these systems were quantified per unit of product and area. The results of both methods showed that the dairy system that emitted the lowest GHG emissions per unit area did not necessarily emit the lowest GHG emissions possible for a given level of product. Consequently, a recommendation from this study is that GHG emissions be evaluated per unit of product given the growing affluent human population and increasing demand for dairy products. The IPCC and LCA methods ranked dairy systems' GHG emissions differently. For instance, the IPCC method quantified that the Confinement system reduced GHG emissions per unit of product by 8% compared with the grass-based system, but the LCA approach calculated that the Confinement system increased emissions by 16% when off-farm emissions associated with primary dairy production were included. Thus, GHG emissions should be quantified using approaches that quantify the total GHG emissions associated with the production system, so as to determine whether the dairy system was causing emissions displacement. The IPCC and LCA methods were also used in this study to simulate, through a dairy farm GHG model, what effect management changes within both production systems have on GHG emissions. The findings suggest that single changes have a small mitigating effect on GHG emissions (,5%), except for strategies used to control emissions from manure storage in the Confinement system (14% to 24%). However, when several management strategies were combined, GHG emissions per unit of product could be reduced significantly (15% to 30%). The LCA method was identified as the preferred approach to assess the effect of management changes on GHG emissions, but the analysis indicated that further standardisation of the approach is needed given the sensitivity of the approach to allocation decisions regarding milk and meat.

Whole-farm models to quantify greenhouse gas emissions and their potential use for linking climate change mitigation and adaptation in temperate grassland ruminant-based farming systems

“…With similar milk production, greater enteric emissions from grazing-based systems is offset by lower manure emissions to provide a lower C footprint for milk produced in grazing systems (e.g. Rotz et al, 2009;O'Brien et al, 2012a and2012b). With a much greater milk production from confinement dairies though, the C footprint of the milk produced may be similar or less than that from a grazing system (Rotz et al, 2010).…”

“…Some models include simple EFs from silage effluent relating the biological oxygen demand to CH 4 production (e.g. Foley et al, 2011;O 0 Brien et al, 2012a and2012b) or relating NH 3 volatilisation losses to silage DM loss (e.g. Schils et al, 2006;Del Prado et al, 2011a).…”

“…Grazing v. confinement production systems Farm models have been used to compare the GHG impacts of grazing systems compared with confinement systems (Arsenault et al, 2009;Anon, 2010;Belflower et al, 2012;O'Brien et al, 2012a and2012b) or gradients of replacing grazing by greater use of maize (Schils et al, 2007b). The total effect on GHG emissions depends on whether the greater enteric emission and soil N 2 O emissions from grazing-based systems compared with confinement systems are counteracted by lower manure emissions.…”

Implications of dairy systems on enteric methane and postulated effects on total greenhouse gas emission

“…High grain diets may also lead to greater methane emission from the manure (Hindrichsen et al, 2006). These studies underline the importance of studying the broader implications of differences in diet among systems on GHG impact in the dairy industry, which include direct (on farm) and indirect (before and after the farm gate) effects (O'Brien et al, 2012b).…”

“…Lower milk production relative to that of cows fed more grain in confinement elevates EM emission per kg milk of grazing cows (Chagunda et al, 2001), a common gage of dairy impact on climate change; however, all inputs and predicted environmental impacts relative to yield of milk were reduced by MIG such that MIG may be considered a GHG mitigation strategy (Phetteplace et al, 2001).…”