Lessons from a next generation carbon ranching experiment

Authors: Reinhart, Kurt; Rinella, Matthew - Matt; SANNI WOROGO, HILAIRE - University Of Parakou; Waterman, Richard; Vermeire, Lance

Submitted to: Global Change Biology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 7/15/2022
Publication Date: 7/21/2022
Citation: Reinhart, K.O., Rinella, M.J., Sanni Worogo, H., Waterman, R.C., Vermeire, L.T. 2022. Lessons from a next generation carbon ranching experiment. Global Change Biology. 425. Article 116061. https://doi.org/10.1016/j.geoderma.2022.116061.
DOI: https://doi.org/10.1016/j.geoderma.2022.116061

Interpretive Summary: Problem- Managing grasslands to sequester carbon is of global importance, but effects of grazing on soil organic carbon (SOC) stocks remain uncertain. In other words, the existing research base isn't adequate to reliably predict where/how to manage livestock to sequester the maximum amount of SOC. Accomplishment- We performed a next generation carbon ranching experiment. After five-years, no grazing and severe summer and fall grazing accrued 0.85 to 1.22 kg × m-2 (0-60 cm soil depth) more SOC than conventional moderate summer grazing and represent appreciable increases in SOC stocks. Unclear is whether these grazing treatments can accrue SOC over longer periods of time (>5 years). While severe grazing may have positive effects on SOC accrual in the short-term (~5 years), severe grazing may negatively impact plant species composition, soil structure, and other ecosystem services.

Technical Abstract: Identifying grazing practices that maximize food production and soil carbon sequestration is of global importance. Currently, we cannot reliably predict which grazing practice will accrue the most soil organic carbon (SOC) partly because of confusion created by an abundance of low-quality experiments. Here we tested the effects of five grazing treatments on SOC stocks with a gold standard randomized controlled trial (RCT) with pre-treatment data. Treatments were no grazing, severe summer grazing, moderate fall grazing, severe fall grazing, and the conventional approach for the system of moderate summer grazing. Because grazing experiments are little-replicated, we gauged the dependence of results on pre-treatment data by comparing the results of analyses with vs without pre-treatment data. We also tested for relationships between plant and soil properties and SOC. After five-years, no grazing and severe summer and fall grazing accrued 0.85 to 1.22 kg × m-2 (0-60 cm soil depth) more SOC than conventional moderate summer grazing and represent appreciable (i.e. greater than 4 per mille per yr) increases in SOC stocks. Furthermore, the entire portfolio of new grazing practices increased SOC accrual compared to conventional management. Given the divergent characteristics of the newly applied practices, sustainable accrual of SOC may depend on management heterogeneity. Accrual of SOC was likely driven by a reduction in SOC mineralization related to increased soil density and nitrogen, decreased root biomass, and change in plant species composition. We found unique results for analyses with and without pre-treatment data, thereby indicating the risk of unreliable results for little-replicated RCTs without pre-treatment data. Well-designed experiments are needed to correctly identify grazing practices that accrue the most SOC.