Use of composted manures and plant materials in farming has a history almost as long as farming itself. California farmers enjoy access to high-quality compost and mulch products from a variety of feedstocks virtually everywhere in the state. California compost facilities permitted in accordance with state law and CalRecycle regulations, and inspected by our network of local enforcement agencies (LEA), meet high standards for pathogen reduction and testing of final product. Additionally, compost facilities selling to organic food producers are inspected annually by the California Department of Food and Agriculture for strict adherence to National Organic Program regulations.

Governor Brown’s administration has recognized the importance of soil health, establishing the Healthy Soils Initiative. With CalRecycle and the California Department of Food and Agriculture as lead agencies, goals for this initiative include building soil organic matter, increasing climate resiliency and maintaining high yields.

Regular use of compost brings many benefits to the farmer. Some of these benefits have been studied. Other benefits are more difficult to quantify, and will vary for farmers based on frequency and amount of compost applied, soil type, crop rotations, and other factors. They include:

  • Increased soil water holding capacity and reduced runoff
  • Beneficial micro-organisms to improve soil health
  • Addition of humus
  • Addition of organic matter and carbon sequestration
  • Improved soil tilth

Compost provides low levels of all primary, secondary and micronutrients. Many micronutrients become depleted from agricultural lands over time and may not be replenished with conventional fertilizers. Compiled analyses of more than 1,600 compost samples from the southwestern United States performed by Soil Control Lab found average levels of these micronutrients.

Case Studies of Compost Use

  • Climate change drives farmer-focused digestate and compost in agriculture research in the United Kingdom. Digestate and compost in agriculture or the DC-Agri Project, is a four year research project on the use of quality anaerobic digestate and compost in agriculture. The results of this research show that digestate and compost can improve soil fertility and provide valuable plant nutrients.
  • GO Compost is making up to 15,000 tons of compost per year from tomato skins and seeds, and other locally sourced materials. GO stands for the partners in the project, General Mills and OLAM.
  • Crop Yields and Plant Health for Growing Processing Tomatoes: Processing tomatoes grown with 10 tons per acre of composted poultry manure achieved yields 9 to 22 percent above controls, according to new research funded by the California Tomato Research Institute and carried out by the University of California Cooperative Extension. Yield increases were most pronounced for soils with potassium levels below 200 ppm.
  • Compost use in large-scale production of salad greens: Michael Brautovich has five watchwords when it comes to purchasing compost for Earthbound Farm, one of the nation’s largest growers of fresh salad mix and organic vegetables. “Quality, safe, consistent, mature, organic” said Brautovich, Earthbound’s senior manager for quality, food safety and organic integrity. “We are looking for compost free of chemical, physical, and biological contaminants.”
  • Compost use on California winery: The Joseph Phelps Winery: Using compost to help capture “terroir”. Sustainable agriculture practices contribute to production of world class wines.
  • Compost use on California rangeland: The Marin Carbon Project is performing a long-term experiment using large quantities of compost to improve forage on California rangeland. Early results suggest significant improvements in forage quality and quantity, benefits to native perennial grasses, and significant soil carbon sequestration. The work includes a suite of farm management practices to compliment compost application in a manner that builds soil carbon and soil health and improves productivity. Each farm has developed a comprehensive carbon farm plan, including known climate-beneficial practices such as windbreaks, riparian and range management improvements, and grass, plant and tree establishment.
  • CalRecycle projects:

Scientific Research on Compost Use



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