Compost and Mulch Use in Agriculture: Organic Materials Management
The agricultural sector uses compost and mulch on annual crops, perennials, orchards, vineyards, and grasslands.
- Compost:
- Provides nutrients in a stable organic form.
- Increases plant growth and health.
- Saves water.
- Mulch:
- Discourages weed growth.
- Maintains soil temperature.
- Saves water.
California Agriculture
Agriculture is the single largest market for compost in California.
California compost facilities are:
- Permitted under state law and CalRecycle regulations.
- Inspected by CalRecycle’s network of local enforcement agencies (LEA).
- Meet high standards for reducing pathogens and testing the final product.
California has committed to using compost on natural and working lands.
Rangeland
Rangelands of open, native grass and plants cover about half of California.
Using compost on rangelands:
- Helps grasses grow.
- Store more carbon climate pollution in the soil.
- Hold water.
The Marin Carbon Project is a long-term experiment using large quantities of compost to:
- Actively pull more carbon climate pollution from the air and store it in the soil.
- And grow more range grass for agricultural grazing.
Organic-Certified Agriculture
For compost to be used in organic-certified agriculture, it must meet USDA National Organic Program (NOP) requirements.
In California, the California Department of Food and Agriculture (CDFA) verifies that the compost meets these requirements through its Organic Input Material (OIM) Program.
For marketing purposes, many organic compost manufacturers also include a separate verification from the Organic Materials Review Institute (OMRI) for compliance with the USDA National Organic Program and other organic standards. But it is not required in California.
Where to Buy Compost in California
- Solid Waste Information System
- Compost Source Locator (U.S. Composting Council)
- Zero FoodPrint
Benefits of Compost and Mulch Use
The positive impacts of compost vary based on:
- How much and how often you apply compost.
- The soil type, crop rotations, and other factors.
Benefits include:
- Improves plant health, growing stronger plants with deeper roots by
- Improves soil tilth condition.
- Gives natural, non-chemical nutrients to plants.
- Supports micro-organisms growth in soil.
- Conserves water by holding more water in soil.
- Stores carbon climate pollution in the soil.
- Reduces erosion.
- Mulch discourages weeds from sprouting and insulates soil temperature.
Compost Use Guidelines
The use of compost depends on soil properties and crop type. Many growers rely on soil testing and crop advisers to determine the right application rates based on properties, including:
- Levels of nutrients and organic matter
- Maturity
- Stability
- pH
- Particle size
- Other parameters
Test compost to ensure it meets specifications.
To help users decide if a compost product is right for their use, the US Compost Council’s Seal of Testing Assurance (STA) Program:
- Uses standardized testing methods in certified labs.
- Reports test results.
Additional Tools and Guides:
- University of California Agriculture and Natural Resources Assessing Compost Quality for Agriculture tool can help estimate initial compost-soil mixture salinity levels.
- The US Compost Council Field Guide to Compost Use
- Compost Research and Education Foundation compost specification sheets for Row Crop Production and Supplementing Plant Nutrition.
On-Farm Composting
Often compost on farms is made from:
- Plant residues and manure produced on the farm.
- Yard trimmings and other materials from cities.
Compost made on farms may be subject to CalRecycle regulations, depending on the:
- Volume of material on-site.
- Amount sold or given away.
- Some other factors.
Agricultural Use of Mulch
Agricultural markets for mulch products continue to grow.
Use mulch in agriculture for:
- Erosion control.
- Disease and weed suppression.
- Water conservation.
- Keeping soil from getting too compacted.
Additional Resources
For more information contact: Compost Use in Agriculture, organics@calrecycle.ca.gov