Quantifying the impact of climate smart agricultural practices on soil carbon storage relative to conventional management

Climate smart agricultural practices have received considerable attention recently for their potential for climate change mitigation through sequestering atmospheric carbon. Despite the enthusiasm for climate smart practices, there is limited evidence they are more effective at removing carbon from the atmosphere and storing it in the soil than current practices. We hypothesized that a field with aspirational (ASP) practices (i.e., no-till corn-soybean-wheat-hay rotation with cover crops) would accumulate more soil organic carbon (SOC) versus a business-as-usual (BAU) field (i.e., conventional-tillage, corn-soybean-soybean rotation). We used deep soil cores (1 m) to assess changes in soil organic carbon (Delta SOC) between 2016 and 2022 for the two fields and compare with estimates based on eddy covariance calculation of Delta SOC. We found that the ASP field had Delta SOC that was positive, and larger than the BAU field. Both the soil sample method (Delta SOCSS) and the eddy covariance method (Delta SOCEC) agreed on this point, but the magnitude of Delta SOC was much larger when estimated with soil samples (Delta SOCSS was 1.9 +/- 1.7 % yr(-1) and-0.7 +/- 1.3 % yr(-1) at ASP and BAU, respectively) than with eddy covariance (Delta SOCEC was 0.80 +/- 0.09 % yr(-1) and 0.12 +/- 0.06 % yr(-1) at ASP and BAU, respectively). Finally, we used the continuous measurements of carbon fluxes from the eddy covariance towers to examine how conservation practices (cover crops, no-till, or expanded crop rotation) led to increased carbon storage. We found that unharvested cover crops add carbon to the soil that offsets net carbon losses that otherwise reduce soil carbon storage when the field is fallow. No-till and expanded crop rotations also affect the carbon budget of the agroecosystems. Results from this study illustrate the value of conservation practices in a changing climate and the value of eddy covariance measurements for assessing climate smart practices.