Updated potential soil carbon sequestration rates on U.S. agricultural land based on the 2019 IPCC guidelines

Abstract

The Intergovernmental Panel on Climate Change (IPCC) recently updated the 2006 IPCC Guidelines to reflect the most current research and information available for countries to accurately estimate their reporting data for greenhouse gas emissions. To report on changes in soil organic carbon (SOC), the IPCC method uses fixed factors to estimate how land-use and management changes affect default reference SOC stocks. The 2019 IPCC Guidelines incorporate additional studies and more recent research to modify the default reference SOC stocks and the factors used to estimate the effect of land use and management changes on SOC stocks. The research presented here applies the 2019 IPCC factors to agricultural land in the conterminous U.S. and compares the results to the same research conducted using the 1996 IPCC factors. Baseline SOC stocks were slightly higher estimated with 1996 IPCC factors compared to 2019 factors (17.1 vs 15.2 Tg C yr−1 (million metric tonnes of carbon per year)), but the source was quite different. Applying the 1996 factors resulted in about 52 percent of the SOC stock increase from land-use-change (LUC) and 42 percent from tillage effects while the 2019 factors indicate about two-thirds of the SOC stock increase was from LUC and one-third from tillage effects. Using the 1996 IPCC documentation provided estimates of annual SOC stock increases of 83.2 Tg C yr−1 for twenty years (66 Tg C yr−1 more than the baseline) from set-aside, including winter-cover crops, eliminating fallow, and no-till adoption. Smaller increases from these same activities are estimated when using the 2019 IPCC factors with a total potential increase of 47.3 Tg C yr−1. The SOC stock increases are predominantly in the wetter regions. The two activities that provide the greatest increase in estimated SOC stocks were from the addition of cover crops, which increased SOC by 17.7 Tg C yr−1 using 2019 IPCC factors compared to 22.8 Tg C yr−1 using the 1996 IPCC factors, and full adoption of no-till which increased SOC by 18.4 compared to 30.3 Tg C yr−1 for the same comparison.