Modeling soil organic carbon dynamics and uncertainty in life cycle assessment of agricultural systems

Abstract

ISO 14067:2018 mandates accounting for land use and land use change (LULUC) impacts on global warming impact due to carbon stock changes in living biomass, litter, dead organic matter, and soil organic carbon (SOC). Furthermore, the SOC changes are particularly relevant for cropland-based products. Despite methodological advancements, there is still no universally agreed-upon approach on how to evaluate LULUC-related global warming impact within Life Cycle Assessment (LCA), highlighting the need for a standardized approach. This study presents a comprehensive method for assessing SOC dynamics due to land use in LCA, incorporating uncertainties associated with model-based estimations. Using the Tier-2 IPCC Steady State Soil Carbon model, the study analyzed SOC changes in sugarcane cultivation on mineral soils in Thailand. The study examined the effects of land use history across different study periods (T-20, T-50, and T-100 years), as well as the impact of land management practices (full-, reduced-, and no-tillage) and residue management strategies (100 % burnt, 100 % retained, and mixed) on SOC change. While the model study period considerably influenced the initial SOC stocks, the variations in soil organic carbon stock change due to study periods, land management, and residue management practices were statistically not significant. However, the model-associated uncertainties were found to be substantial. The distribution fit assessment revealed that CO₂ emission/removal related flow follows a normal distribution [X ~ N (μ, σ²)]. Our findings highlighted the importance of incorporating ∆SOC into carbon footprint calculations to accurately capture the carbon sequestration potential of soils, which can significantly offset emissions. Neglecting SOC dynamics may lead to an overestimation of CO₂ emissions and an incomplete assessment of net carbon impact. Therefore, given the significant variations observed in global warming impact, integrating SOC considerations into LCAs is essential for improving the precision of environmental evaluations of agriculture-based products.