Assessing the environmental impact of ruminant production systems

Taro Takahashi, Graham A. McAuliffe, Michael R.F. Lee

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As discussed elsewhere in this book, one of the most common methods to evaluate environmental footprints of farming systems is life cycle assessment (LCA). Although LCA itself is suitable for and indeed adopted by a wide range of industries far beyond agriculture, what separates agriculture, and in particular pasture-based ruminant production systems, is the high degree of uncertainties associated with physical, chemical and biological processes that underpin production (McAuliffe et al., 2018a). In the presence of uncertainties, point-estimates provided by LCA models are unlikely to be informative enough to offer robust policy implications (Chen and Corson, 2014); when this is the case,
the resultant environmental burdens must be expressed in the form of probability distributions and interpreted accordingly (McAuliffe et al., 2017). For carbon footprint (CF) analysis of ruminant systems, one significant challenge of collating a life cycle inventory is uncertainty associated with emission factors (EF), or parameters linking nutrient inputs into the system to greenhouse gas (GHG) emissions arising from the system (Pouliot et al., 2012). On commercial livestock farms, various factors can affect their relationships; for example, weather, soil, plant/animal genetics, management practice and interactions between them. Despite these variabilities, the majority of LCA studies adopt EFs derived outside the actual system boundary, most commonly as parameters defined as part of Intergovernmental Panel on Climate Change guidelines (IPCC, 2006). As these “generic” EFs are designed to be applicable to a wide spectrum of production environments within a single agroecological zone, a considerable level of uncertainty
surrounds each of these values (Dudley et al., 2014). As a case in point, the two parameters for nitrous oxide (N2O) emissions suggested by IPCC (2006), commonly known as EF1 (% fertiliser N lost as N2O) and EF3PRP (% urine and dung N deposited on pasture lost as N2O), are both deemed to have a 95% confidence interval between −67% and +300% of the respective point estimates. To facilitate evidence-based debates about the environmental impact of ruminant production systems and, by extension, the role of ruminants in global food security, it is therefore imperative to improve reliability of EFs in a more location-specific context. This, however, requires a significant investment into field-based research, something that is not always feasible for practical reasons. Through a review of recent literature and a quantitative case study, this chapter explores how this practical trade-off between feasibility and scientific rigour should be addressed.
Original languageEnglish
Title of host publicationAssessing the environmental impact of agriculture
EditorsBo Weidema
Place of PublicationCambridge
PublisherBurleigh Dodds Science Publishing
Number of pages18
ISBN (Print)9781786762283
Publication statusPublished - 27 Aug 2019

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