68. Impact of Transitioning to Adaptive Multi-paddock Grazing on Soil Carbon and Ruminant Greenhouse Gas Footprint in the Southeastern US.

Abstract Adaptive multi-paddock (AMP) grazing has been proposed as a strategy to reduce the greenhouse gas (GHG) footprint of beef production by enhancing soil organic carbon (SOC) accrual. Few life cycle assessments (LCAs) of AMP systems have incorporated measured SOC change, and none have evaluated transitional AMP systems-where grazing management is in place but animal productivity remains below regional potential-so the climate benefits of such systems are uncertain. We conducted a farm-scale LCA using four to six years of on-farm animal productivity and SOC data from a Tennessee beef and sheep operation that had recently adopted AMP grazing. The Transitional AMP system (TR-AMP) reflected current management and documented beef herd underperformance. We compared it with two alternative beef systems scaled to the same annual beef output: an Advanced AMP system (AD-AMP), representing a productive AMP scenario, and a Business-as-usual system (BAU), representing the regional conventional cow-calf, backgrounding, and feedlot pathway. In all three scenarios, sheep were included under the farm’s current AMP management. We quantified GHG emissions from enteric fermentation, manure, feed production, on-farm energy, and transport, and we measured SOC stocks in the top 30 cm over the study period. We did not detect a statistically significant change in SOC (p > 0.05); we therefore did not include SOC as a quantified sink in the main footprint and report gross emissions. For combined beef and sheep, GHG intensity was 40.6, 30.5, and 23.2 kg CO2-e kg-1 carcass weight (CW) for TR-AMP, AD-AMP, and BAU, respectively; for beef only, the values were 47.0, 33.1, and 22.5 kg CO2-e kg-1 CW. TR-AMP used 172 ha, AD-AMP 89 ha, and BAU 79 ha. Differences in weaning rate, finishing age, average daily gain, and stocking rate aligned with these differences in land use and GHG intensity. A sensitivity analysis using a literature-based SOC accrual rate of 0.28 Mg C ha-1 yr-1 showed that, were such a rate achieved on grazingland, net intensity could fall to 23.1, 21.9, and 16.6 kg CO2-e kg-1 CW for TR-AMP, AD-AMP, and BAU. We conclude that in this context herd performance–not AMP grazing label alone–was a key driver of GHG intensity, and that SOC did not provide a statistically robust sink over the period observed. For AMP to deliver meaningful GHG benefits, it likely needs to be paired with strong reproductive and growth performance, and short-term expectations for large SOC-based offsets in transitional systems should be tempered.