A long-term study at the University of California Davis Russell Ranch Sustainable Agriculture Facility, in the western U.S., found that practices that increase soil organic carbon, such as compost, helps increase long-term soil carbon storage. 


For the 19-year study, scientists dug more than 1.2 meters (6 feet) deep in plots that had been in a variety of systems in a semi-arid region. Their findings demonstrated the complexity of carbon in supporting soil health. The study summary explains:

  • Conventional soil management systems neither release nor store much carbon.
  • Cover crops increase carbon in the top 30 cm (12 inches) of soil, but surprisingly lose carbon deeper in the soil.
  • Adding both compost and cover crops increased soil carbon content about .07% per year, for a total increase of 12.6% during the study.


The researchers attribute these findings in part to the nutrient needs of microbes that maintain soil health. Adding nutrient-rich organic matter like the poultry compost used in this study may improve soil health – and its ability to store carbon. 

The full study details the soil systems compared since 2000.