Cover crops and carbon sequestration: Lessons from US studies

Sequestering soil organic carbon (SOC) with cover crops (CCs) to mitigate climate change and enhance other soil ecosystem services is generating much enthusiasm. However, the potential of CCs to sequester large amounts of SOC appears to be debatable, which warrants further discussion on regional and national scales. This paper discusses both CC effects on SOC based on studies in the United States up to 30 May 2021 and practices that could enhance CC ability to sequester SOC. Cover crops accumulated SOC only in 22 (29%) of 77 comparison (CC vs. no CC) counts. Cover crops accumulated 0.2-0.92 Mg C ha(-1) yr(-1) (0.41 Mg C ha(-1) yr(-1) average) across the 22 comparisons where CCs increased SOC and 0-0.92 Mg C ha(-1) yr(-1) (0.12 Mg C ha(-1) yr(-1) average) across the 77 comparisons in the upper 30-cm soil depth. Cover crops increased SOC most in low-C soils (<1% C) and after 5 yr but not when CCs produced <2 Mg biomass ha(-1). Because SOC accumulation was primarily correlated (r = .38; p = .006) with CC biomass and years under CCs (r = .37; p = .009), current CC management practices need modification to enhance SOC accumulation. Planting after crop harvest in summer and terminating late to increase CC biomass production along with long-term (>5 yr) use can be potential strategies. Overall, CCs can accumulate SOC only in one-third of cases based on U.S. studies, which urges the modification of current CC management practices to boost SOC sequestration.

Automated summary

The potential of cover crops to sequester soil organic carbon is debated and further research is needed. Cover crops only increased soil organic carbon in a fraction of cases, with biomass and years of cover crop cultivation being key factors. Current management practices for cover crops should be modified to enhance soil organic carbon accumulation.