GC012-05
Greenhouse Gas (GHG) Accounting in Agricultural Supply Chains
Greenhouse Gas (GHG) Accounting in Agricultural Supply Chains
Monday, 7 December 2020: 07:16
Virtual
Abstract:
Ambitious agricultural supply-chain GHG reduction initiatives require practical yet scientifically-robust methods to quantify net GHG emissions. Engagement with stakeholders reveals that assessment of supply-chain GHG emissions must be conducted with limited and spatially-aggregated data. GHG accounting in large supply chains is typically implemented by commodity aggregators, wholesalers and retailers with limited long-term connections to a particular farm resource base and without detailed farm-level management knowledge.
These data-limited conditions create a tension between simplification versus comprehensive and reliable accounting. Accordingly accounting tools that prioritize simplicity over comprehensive analysis are proliferating. Examples include accounting methodologies that measure only soil organic carbon but ignore other GHG sources or sinks. To address this tension, we developed a GHG accounting methodology for assessment of commodity grains in U.S. supply chains. Our method accounts for cover-crop, tillage-regime, and fertilizer-management impacts on soil organic carbon (SOC), nitrous oxide (N2O) emissions, fertilizer and seed production, on-farm energy use, leakage due to changes in crop yield, and permanence, while requiring very few input parameters. We thus show that the key drivers of net GHG emissions vary with location, with crop yield, N2O, and fertilizer production often dominating over SOC. Improved monitoring of yield and N impacts of agricultural best management practices is therefore critical and often lacking in simplified methodologies. The importance of leakage indicates the need for coordinated implementation of sustainable agricultural practices such that existing demand for commodity crops does not drive unsustainable practices elsewhere.
These data-limited conditions create a tension between simplification versus comprehensive and reliable accounting. Accordingly accounting tools that prioritize simplicity over comprehensive analysis are proliferating. Examples include accounting methodologies that measure only soil organic carbon but ignore other GHG sources or sinks. To address this tension, we developed a GHG accounting methodology for assessment of commodity grains in U.S. supply chains. Our method accounts for cover-crop, tillage-regime, and fertilizer-management impacts on soil organic carbon (SOC), nitrous oxide (N2O) emissions, fertilizer and seed production, on-farm energy use, leakage due to changes in crop yield, and permanence, while requiring very few input parameters. We thus show that the key drivers of net GHG emissions vary with location, with crop yield, N2O, and fertilizer production often dominating over SOC. Improved monitoring of yield and N impacts of agricultural best management practices is therefore critical and often lacking in simplified methodologies. The importance of leakage indicates the need for coordinated implementation of sustainable agricultural practices such that existing demand for commodity crops does not drive unsustainable practices elsewhere.