An interesting and important study conducted for 19 years by the USDA National Institute of Food and Agriculture and the UC Davis College of Agriculture and Environmental Sciences, found that practices that increase soil organic carbon, such as the use of compost, help increase long-term soil carbon storage.
By moving beyond the surface level and literally digging deep, scientists at the University of California, Davis, found that compost is a key to storing carbon in semi-arid cropland soils, a strategy for offsetting CO2 emissions.
- Conventional soils neither release nor store much carbon.
- Cover cropping conventional soils, while increasing carbon in the surface 12 inches, can actually lose significant amounts of carbon below that depth.
- When both compost and cover-crops were added in the organic-certified system, soil carbon content increased 12.6 percent over the length of the study, or about 0.07 percent annually.
That is more than the international “4 per 1000” initiative, which calls for an increase of 0.04 percent of soil carbon per year. It is also far more carbon stored than would be calculated if only the surface layer was measured.
Carbon has to filter through soil microbes to create stabilized forms of carbon in soil. Compost provides not only carbon but also additional vital nutrients for those microbes to function effectively. One reason that explains losing organic matter from soils is that the focus is on feeding the plant, and on forgetting the needs of others who provide important services in soil like building organic carbon.
The results also indicate an opportunity for compost to provide multiple, interconnected benefits to farmers and the environment by improving soils, off-setting greenhouse gas emissions, and transforming animal and food wastes into a valuable product the soil needs.