Results from a long term study on carbon sequestration in California soils were recently published in the Agronomy Journal. A team of UC Davis soil scientists, Cooperative Extension advisers, and USDA Natural Resources Conservation Service partners carried out the project, and found numerous co-benefits associated with reduced tillage and cover crop use.

The study was conducted from 1999 to 2009 at the UC West Side Research and Extension Center in the San Joaquin Valley. Researchers focused on the effects of conservation tillage and cover cropping on carbon storage, water use, and yield in tomato-cotton rotations. Most crop production in the San Joaquin Valley relies heavily on costly, intensive tillage for its presumed benefits to crop establishment and yield, but this study shows that conservation tillage offers far greater benefits.

Researchers compared standard and reduced tillage systems with and without cover crops. During most years, a cover crop mixture including triticale, rye, and peas was planted in November, and was then chopped and either disked in (on standard till plots) or left on the surface (on reduced till plots) the following March. Over the ten-year study, plots where the rainfed cover crops were planted captured more carbon in soils than those without. 

The largest gains in soil carbon were found in reduced tillage plots where the winter cover crop was planted, demonstrating the importance of combining conservation practices in a whole-farm system approach to maximize climate benefits. This combination has other important co-benefits such as increased yield, reduced dust, stabilized soil carbon, reduced water use, and decreased tractor use. In this study, reduced tillage cut tractor operations by 50% for tomato and 40% for cotton, providing significant labor and fuel savings.

Leading author Jeff Mitchell noted the significant rise in soil carbon in the reduced till cover crop plots: soil carbon increased from baseline levels of about 8.8 tons per acre, to 12.9 tons per acre– a nearly 47% rise. Quantifying the potential for carbon sequestration in agricultural soils is an important step toward including farmers in the carbon market. “Providing a stable storage location for carbon could allow agriculture to be part of future cap and trade programs,” Mitchell said.

CalCAN agrees that supporting California agriculture with cap-and-trade dollars is a smart idea. This is why we are sponsoring the Agriculture Climate Benefits Act, SB 367, which would establish a competitive grants program to fund on-farm demonstration projects such as this that reduce greenhouse gas emissions or sequester carbon.

Read more about this study here.