Agricultural Demonstration Projects

Compost and Mulch

The California Integrated Waste Management Board (CIWMB)–now known as the California Department of Resources Recycling and Recovery, or 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.

The primary methodology and results from each project are summarized below, including the project involving the use of green material or compost to suppress Phytophthora cinnamomi in mulched avocado orchards. The demonstration results have been excellent, showing promise for erosion control or disease suppression in some crops. Numerous growers had never used compost, composted mulch or green waste previously and were willing to experiment with these products made primarily from curbside-collected, yard trimmings. Many of the participating growers continue to use one or more products as part of their normal growing practices.

Abstracts of the Demonstrations

Thirteen demonstration projects focusing on agricultural or soil erosion issues promote use of curbside-collected green material. General agricultural production concerns were common to each of the initial five agricultural demonstrations that were conducted for three growing seasons during 1994-1997.

The following are abstracts of the demonstration final reports. The reports can be downloaded via the Internet from CalRecycle’s online publications catalog.

Apricots, cherries, grapes, peppers, radicchio, strawberries, tomatoes, walnuts. Compost Demonstration on the Use of Yard Trimmings Products
Agriculture in Partnership with San Jose investigated the use of fresh yard trimmings, semi-mature compost, and mature compost (produced commercially and on farm). Commercial crops in Alameda, San Benito, and Santa Clara counties included apricots, cherries, grapes, peppers, radicchio, strawberries, tomatoes, walnuts, and Christmas trees.

Test results show that composting effectively eliminates weed seed viability. Composting for 30 days usually kills all weed seeds. Fresh yard trimmings can contain substantial numbers of viable seeds and would not be suitable for applications where weed growth is a concern.

Baby lettuce, broccoli. Maximizing Benefit and Utilization of Compost in Vegetable Production

Presents data from field trials studying the effects of using compost in the intensive vegetable production systems of the Salinas Valley, and examines factors that could influence the use of composts made with municipal organic materials.

Baby lettuce, cabbage, celery and baby greens. Compost Maturity and Nitrogen Release Characteristics in Central Coast Vegetable Production
Report characterizing three compost types produced within the Pajaro River Watershed–green waste, poultry manure, and blends of green waste and poultry manure. Field tests evaluated quantitative maturity index and determined the effect of compost characteristics and maturity on nitrogen (N) release in soils of different textures (sandy, loamy, and clayey). Comparisons were derived regarding crop performance and nitrogen uptake in response to compost type and maturity status. Compost quality was also linked to potential agronomic/economic benefits for differing soil types.

Broccoli, cauliflower, lettuce, onions, potatoes and beets. Compost Demonstration: Monterey Bay Region
The Monterey Bay project demonstrated the value of on-farm composting and increased awareness of the potential benefits of compost use in Monterey, San Benito, and Santa Cruz counties on plots of broccoli, cauliflower, lettuce, onions, potatoes, and beets.

The trial findings range from significant suppression of plant disease to crop pest damage due to an unusually high population density of a soil inhabiting insect. Compost applications appeared to influence soil nitrogen dynamics and soil microbiology. One cannot assume that all composts will provide the same benefits considering the diversity of soils, crops, and management practices.

Caltrans roadside revegetation Compost Demonstration Project, Placer County: Use of Compost and Co-Compost as a Primary Erosion Control Material

The University of California, in cooperation with Caltrans, evaluated several composts and green waste as potential erosion control materials. The initial phase of this U.C. product characterization study was completed in 1999.

The U.C. research project was designed to (1) help develop specifications for using compost for roadside re-vegetation, (2) evaluate its performance for erosion control, (3) evaluate the availability of nutrients for roadside vegetation, and (4) develop a roadside demonstration project in Placer County.

Citrus and Avocado Compost Demonstration Project, Southern California : Use of Yard Trimmings and Compost
In January 1997, CIWMB, the City of San Diego, the City of Los Angeles, and the County of Santa Barbara financed a compost and green waste demonstration in a four-county area of Southern California. In cooperation with the University of California, avocado and citrus orchards were evaluated for disease suppression of Phytophthora cinnamomi over a two-year period.

Citrus. Mulch Demonstration Project Brochure, “Stop Runaway Soil, Use Mulch”

The Ventura County Resource Conservation District (RCD) project completed in 2000 investigated the use of cover crops and green waste mulch for erosion control in citrus orchards. U.C. farm advisors documented the erosion control benefits of green material use on citrus orchard floors.


The two-page color brochure containing the project results is available for downloading from the CalRecycle website publications catalog.

Corn, tomatoes and watermelon. Compost Demonstration: Stanislaus County

The Stanislaus County trials measured benefits of compost use on ornamental nursery stock and field crops. The nursery trials were conducted for two years and the field crops for three years.

In the nursery trials, pre-plant soil tests showed that potting media containing compost has greater nutrient-holding capabilities than media lacking compost, especially for nitrogen. For most of the plants tested, 25 percent compost and potting soil mix performed best. For the field crops, trials on sandy, acidic soils showed that compost treatment beneficially changed soil structure, significantly increased soil organic matter, and raised soil pH. The finely textured compost also increased the soil’s water-holding capacity. This may have implications for water savings in field crop production and potted plants.

A fact sheet that summarizes the findings of this report, Avocados Grow Better with Chips, is also available. (Pub. #443-99-020)

Peach trees Compost Demonstration: Fresno County
Composted green waste was applied in a commercial “Elegant Lady” peach orchard over a multi-year period. Data shows that green waste compost can furnish the necessary level of nutrients to commercial peach trees and compares favorably to other fertilizers used for stone fruit production.

Fruit yields, size, quality, and post-harvest parameters were not significantly different among the treatments. No increase in either disease or insect damage was noted where compost was used. In one year, evidence showed that brown rot disease was significantly reduced when compost was used. Brown rot levels during the following two years were so low that validation of this observation was not possible.

Vineyards. Compost and Mulch Demonstration Project, Mendocino County: Use of Compost and Mulches for North Coast Vineyards
U.C. researchers investigated the impact of using compost in phylloxera-infested vineyards of Mendocino County. An erosion control trial was also conducted using compost wood-overs in another vineyard. The initial phase of the U.C. phylloxera project was completed in 2002.


No treatment effects were seen regarding what impact the compost had relative to phylloxera populations present following two seasons for a variety of reasons. Therefore, the U.C. researchers elected to make design adjustments and study the most recent, phylloxera-infested vineyard for up to five years. The erosion control results with compost wood-overs were excellent using an application rate of eight tons per acre. The compost wood-overs provided initial erosion control and helped in the establishment of a cover crop.

Vineyards. Mulch Demonstration Project Report, “Utilization of Composted Mulch for Erosion Control in Hillside Vineyards”

The Napa County Resource Conservation District (RCD) partnership involved commercial vineyards in the Napa Valley and Sonoma County. U.C. farm advisors from Napa and Sonoma counties investigated the use of composted mulch in the vine row only to control soil erosion in four California vineyard plots. This erosion control project was completed in 2001.

Vineyards. Mulch Demonstration Project Report, “The Effects of Green Material Mulches on Erosion and Dissolved Organic Nutrient Loss from Recently Disturbed Hillside Vineyard Soils”
The Upper Valley Recycling (UVR) partnership investigated alternative materials that might prove useful for erosion control in commercial vineyards in the Napa Valley. The partnership researchers evaluated partially composted green waste in this erosion control project that was completed in 2001.

The UVR demonstration project compared the effectiveness of using composted mulch generally broadcast in three California vineyard plots vs. the traditional straw treatment to control soil erosion. The report includes data tables, graphs, and charts as well as cost-benefit analyses, specifications for mulch production, and application guidelines.

Wheat, cotton, silage corn Compost Demonstration: Tulare County
The Tulare project demonstrated the use of green material compost. Cotton was planted in the first year of the demonstration. Pre-plant fertilizer was applied to all treatments. During that season, nitrogen was side-dressed on all treatments, but the compost and manure treatments received 60 pounds less nitrogen per acre than the conventional.


Wheat was planted after cotton. A second compost application followed the harvest of winter wheat prior to planting silage corn. In addition to the original compost treatments, compost was applied at the rate of 20 tons dry weight per acre during 1996 on either side of the initial demonstration.

For more information contact: Compost Use in Agriculture,