Including long-term soil organic carbon changes in life cycle assessment of agricultural products

Abstract

Regional values for prospective soil organic carbon (SOC) change in Australian cropland were derived via state-of-the-art modelling. This paper evaluates the applicability of the results in the context of life cycle assessment (LCA). Results of soil carbon modelling need to align with LCA requirements in order to be applicable. The following aspects were investigated in more detail: effect of SOC and variability on product carbon footprint results, data symmetry and consistency, attribution of the SOC change to activity and allocation of the SOC change to crops in rotations. Results show that greenhouse gas (GHG) emissions or removals associated with SOC change even in the absence of recent land use change or land management change can potentially change Australian crop carbon footprints considerably. Over a modelling period of 62 years, the SOC continues to change. In attributional LCA, issues with attribution, allocation and data symmetry of the SOC change values are complex. Without a comprehensive understanding of the causal link between individual crops and pasture in a rotation and the change in SOC, and without a SOC change figure for an appropriate reference baseline, application in attributional LCA is limited to certain types of studies only. In consequential LCA, the data symmetry issues as well as the need for allocation and attribution can be avoided. The SOC change results cannot be allocated to individual crops and are therefore valid only for a full rotation cycle. This means results may be applied in attributional LCA but only in certain contexts. The main applicability is foreseen as a business-as-usual baseline for consequential LCA. A set of SOC change values will be derived for this purpose and made available with accompanying guidance for use and interpretation.