Towards a common nutrient use efficiency assessment method for livestock supply chains: a case study of mixed dairy supply chains in western europe

The comprehensive assessment of efficiency of nitrogen (N) and phosphorus (P) use in livestock supply chains is a key step towards sustainable nutrient management [1]. Previously, we identified supply chain level nutrient use efficiency (life-cycle NUE), as a pertinent indicator to support monitoring of practice changes and benchmarking of livestock supply chains [2]. The quantification of life-cycle NUE [3] requires the computation of NUE at each stage of supply chain, including crop/pasture production, animal production and processing. A ‘perfect’ NUE assessment in crop/pasture production would require measurement of all nutrient flows, including inputs, soil stock changes (SSC), losses and removals in harvested biomass. However, no dataset could be found that includes comprehensive measurement of both SSC and losses. Therefore, existing models commonly estimate the value of these variables by modelling one of these two flows and deriving the other from mass balance. The aim of this study, part of the FAO Livestock Environmental Assessment and Performance (LEAP) partnership, was to assess the extent to which reported life-cycle NUE values depend on such methodological choices. We compared three N accounting approaches: i) a simple input-output approach where SSC is set to equal 0 [4], ii) an approach where N losses are modelled [5] and iii) an approach where SSC is modelled, based on assumptions about NUE values [6]. Additionally, for P-NUE, we explored methodological approaches to account for “sustainable fertility build-up” in P-deficient and optimum soils [7]. We illustrate both these N and P assessments for mixed dairy systems in Western Europe.


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