University of California-Davis Study Finds Compost is Key to Sequestering Carbon in Soil

Researchers at the University of California at Davis recently published the results of a 19-year study into the carbon storing potential of conventional soils versus cover-cropped and compost-added soils. Unlike previous studies, UC-Davis scientists dug down 6 feet to measure carbon content, not just 12-inches as with conventional soil studies. The study was published in the journal Global Change Biology.

The study team looked at changes in soil carbon content and found that conventional soils did not release or store much carbon. They found that cover cropping conventional soils increased the carbon content in the first 12-inches of soil but actually lost carbon content below that top layer of soil. With compost added to cover-cropped soils, the researcher found that carbon content increased 12.6% over the term of the study – or about 0.7% annually. The international “4 per 1000” initiative is pushing for an increase of 0.4% in soil carbon content per year as a way of combating climate change. UC-Davis’ results using compost promise more carbon sequestering, especially when looking deeper than just the surface layer.

In the UC-Davis press release about the study, cropping systems scientist Nicole Tautges from UC-Davis’ Agricultural Sustainability Institute, commented on the carbon storage potential of conventional soils and cover crops, saying “We’d make more progress by incentivizing compost.”

The research, which was funded by the U.S. Department of Agriculture, will have important implications for agricultural incentive programs. It also suggests we have not been properly measuring carbon levels in soils. The researcher at UC-Davis plan to continue studying soil carbon content, looking at compost alone, without cover crops. The results will inform strategies for offsetting CO2 emissions.