Compost and Mulch Use in Agriculture: Organic Materials Management

Use of composted manures and plant materials in farming date to the earliest beginnings of agriculture. Modern agriculture uses compost and mulch on annual crops, perennials, orchards, vineyards, and grasslands. Compost improves soil properties, provides nutrients in a stable organic form, increases plant growth and health, and conserves water. Mulch reduces weed germination, moderates soil temperature, and conserves water.

Croplands with compost

California Agriculture

Agriculture is the single largest market for compost in California. The California Compost Coalition estimates irrigated cropland in the state uses 7.5 million tons of bulk compost annually. California farmers enjoy access to high-quality compost and mulch products 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, California Department of Food and Agriculture conducts annual inspections of compost facilities that sell to organic food producers to ensure strict adherence to National Organic Program (NOP) regulations. The Third Assessment of California’s Compost and Mulch-Producing Infrastructure identified the major crop types using compost in California.

Organic Agriculture

In 2015, according to CDFA, organic agriculture in California grew to 687,000 acres and topped $2.2 billion in value, which represents approximately 40% of the nation’s organic production. Organic crop inputs, such as compost, are required to meet USDA National Organic Program (USNOP) requirements. The California State Organic Program (CASOP) is the only program approved by the USDA National Organic Program, and it is co-administered by the California Department of Food and Agriculture (CDFA) for organic producers and the California Department of Public Health (CDPH) for organic products. The CASOP oversees production and handling operations within the state. The Organic Materials Review Institute (OMRI) provides an independent review of compost products for organic farming. Many growers use OMRI-certified compost to ensure it is compliant with USNOP requirements.


Rangeland ecosystems cover approximately half the land area of California. In the last several years, there has been a movement to use enhanced land management or conservation agriculture practices, including compost use, to increase carbon sequestration (i.e., long-term storage of carbon in soils and vegetation) on these lands. Compost use on rangelands increases grassland productivity, carbon sequestration, and water conservation.

Cows in Pasture

Benefits of Compost and Mulch Use

Regular use of compost and mulch brings many benefits to the farmer. Benefits will vary for farmers based on frequency and amount of compost applied, soil type, crop rotations, and other factors. Benefits include:

  • Improves plant growth and health
  • Provides organic matter
  • Provides plant nutrients in a stable organic form
  • Improves soil tilth
  • Beneficial micro-organisms to improve soil health
  • Sequesters carbon
  • Increases plant rooting depth
  • Improves physical, biological, and chemical soil properties
  • Reduces erosion
  • Increases water holding capacity and reduces runoff
  • Conserves water
  • Mulch reduces weed germination and moderates soil temperature


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 these levels of micronutrients.

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 complement 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.

Read about the ‘4 per Thousand’ initiative, launched at the Paris Climate conference, to implement practical actions on soil carbon storage and encourage ag and other stakeholders to transition towards a productive, highly resilient agriculture that creates jobs and ensures sustainability.

Compost Use Guidelines

Compost characteristics and application rates for crops are dependent on soil properties and crop type. Many growers rely on soil testing and crop advisers to determine suitable compost application rates based on compost properties, including levels of nutrients and organic matter, maturity, stability, pH, particle size, and other parameters.

Test compost to ensure it meets specifications. The USCC’s Seal of Testing Assurance (STA) Program uses standardized testing methodologies, certified laboratories, and reports test results so that users can determine if a given compost product is suitable for its intended use.

Crop-specific salinity thresholds require that growers consider compost salinity, pre-compost salinity, compost application rate, soil organic matter, and soil texture. A tool developed by UCANR (see p. 5 of Assessing Compost Quality for Agriculture) allows growers to estimate initial compost-soil mixture salinity levels.

USCC Field Guide to Compost Use

Compost Research & Education Foundation – Compost Specification Sheets for Row Crop Production and Supplementing Plant Nutrition.

Agricultural Use of Mulch

Agricultural markets for mulch products continue to grow, most of which is green material applied to agricultural land as mulch. Use mulch in agriculture for erosion control, disease and weed suppression, water conservation, and to reduce soil compaction and allow access after heavy rainfall.

On-Farm Composting

Agriculture uses compost produced both outside and on-farm. On-farm compost, produced from plant residues generated on the farm as well as yard trimmings and other materials from cities, provides many benefits. On-farm composting may be subject to CalRecycle regulations, depending on the volume of material on site, amount sold or given away, and other factors.

Food Safety

Rules, regulations, and agreements ensure organic inputs such as compost protect food safety.

Grant Funds for Agriculture

Grant funds assist agriculture in improving soil health by building soil organic matter with compost and mulch, and cleanup of illegal solid waste sites on farm or ranch property.

Healthy Soils Initiative. In 2015, Governor Brown’s administration, recognizing the importance of soil health, established the Healthy Soils Initiative, with CalRecycle and the California Department of Food and Agriculture (CDFA) as lead agencies. Goals for this initiative include building soil organic matter, increasing climate resiliency and maintaining high yields. The Healthy Soils Program (HSP) provides grants for projects that use compost and mulch, the HSP Incentives Program and the HSP Demonstration Projects. The HSP Incentives Program provides grants for projects that implement conservation management practices that improve soil health, sequester carbon, and reduce greenhouse gas (GHG) emissions. The HSP Demonstration Projects provides grants for on-farm demonstration projects that conduct research and/or showcase conservation management practices that reduce GHG emissions and improve soil health and create a platform promoting widespread adoption of conservation management practices throughout the state.

Farm and Ranch Solid Waste Cleanup and Abatement Grant Program. CalRecycle’s Farm and Ranch Cleanup Grants provides up to $1 million annually in grants for cleanup of illegal solid waste sites on farm or ranch property zoned for agricultural use where unauthorized solid waste disposal has occurred.

Compost and Mulch Use

  • Agricultural Demonstration Projects. CalRecycle funded various partnerships that proposed large-scale demonstrations between 1994 and 2002. These partnerships involved commercial growers throughout California monitoring the effects of compost, composted mulch or green material (e.g., yard trimmings) on various commodity crops by examining one or more of the following–crop yields, incidence of plant disease, compost characteristics, soil profiles, or measurable soil erosion.

Where to Buy Compost in California

Additional Resources

For more information contact: Compost Use in Agriculture,