Use of Wood Ash as Soil Amendment on Annual Rangelands

Final Report for FW11-037

Project Type: Farmer/Rancher
Funds awarded in 2011: $28,995.00
Projected End Date: 12/31/2013
Region: Western
State: California
Principal Investigator:
Mel Thompson
Sierra Farms
Glenn Nader
University of California Cooperative Extension
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Project Information


This project attempted to quantify benefits from the use of wood ash on rangeland. Five locations were chosen, representing soil diversity typical of Butte County. Plots were 50’x100’, with ash spread at two rates, 10 and 20 tons/acre, on opposite strips within the plot. Four exclusion cages were used on the treated areas; two per application rate and one in non-treated adjacent area as a control sample.

Sporadic, insufficient rainfall during the 2012 season prevented ash from filtering into the soil profile and produced so little forage that valid measurement was difficult. The project was extended one year, which resulted in slightly better conditions. Sampling occurred in May and June 2013 and is included in this report.

Generally, response to potassium was greatest, showing in positive legume growth, with moderate nitrogen and phosphorous response. Rainfall amounts and timing varied across the five locations and seem to be the most significant variables in test results. Ideally this study should proceed for several more years in order to get a better assessment over average rainfall amounts.


Based on prior, non-technical trials, the use of wood ash was seen as having noticeable positive results in production of legumes found in local annual rangelands. Species shifting toward increased legume content is a positive trend in rangeland livestock husbandry, wherever possible.

Fly ash is a by-product of co-generation facilities that use ag and forest wood waste to turn steam-powered electrical generators. Recent interest in forest management and orchard replacement, combined with incentivized alternative energy production, has increased the potential for ash production. Prior ash waste from the local plant was being trucked approximately 100 miles to a landfill. Local ash usage on rangeland was seen as beneficial to both the co-gen facility and local farmers and rangeland owners. Approximately 16,000 tons per year would treat 800-1600 acres annually.

The local plant employees 35 persons and contributes approximately $50 million yearly to the local economy in wages and associated business activity. Ash waste removal was a $1 million or more expense to the facility, while being a lost opportunity as a soil amendment. This study attempted to merge the two circumstances to the benefit of each.

Rangeland soils in Butte County tend to be slightly acidic, red clay loam with surface rocks and underlying hard pan or lava cap. These conditions have discouraged attempts at cultivation even on relatively level terrain. Vegetation is mostly annual grasses and forbs, with major invasions of medusahead and yellow starthistle. Plant diversity is fair and plant density (soil coverage) often is very low. Initial trials with wood ash have shown dramatic improvement in forage growth without seeding, especially in annual legumes. The native annual legume seedbank is present, while ash, with high potassium and moderate phosphorous, sulphur and nitrogen levels seems to be the catalyst. High calcium levels tend to loosen the clay structure, allowing improved soil porosity, water infiltration and reduced runoff.

Project Objectives:

The objectives of the project were:

1. Determine best means and rate of ash application, considering area coverage, labor requirements, vegetation response and impact on RDM.

2. Analyze soil and vegetation differences between ash-treated and untreated areas.

3. Determine forage production changes.

4. Record changes in plant diversity and density.

5. Observe changes to soil texture, porosity and infiltration rates.

6. Determine if grazing season has lengthened.

7. Provide outreach to other ranchers and interest groups as to findings, benefits and unforeseen problems.

8. Provide outreach to co-generation plant owners on ash usage, application requirements, time of use and other issues specific to rangeland application.

9. Determine if carbon sequestration is enhanced by ash usage on annual rangelands.

10. Publish findings and post on website.

The overriding objective is to expand on observed vegetation changes found in earlier experiments and make ash application acceptable to a wider group of ranchers, while simultaneously anchoring the local biomass conversion facility by demonstrating safe, feasible means of utilizing its ash by-product.

A long-range objective is to form an LLC of rangeland owners to contract ash dispersal from the facility, with the ability to absorb full application accountability for the product's safe usage. Biomass conversion plants commonly pay for ash removal, which, if possible, could add more incentive toward improving range conditions, as well as serve as a model for similar applications in other areas.


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  • Dr. Pelayo Alvarez
  • Dave Daley
  • Valerie Eviner
  • Holly Foster
  • Mitchel Gorsky
  • Steve Lambert
  • Wallace Roney


Materials and methods:

Fly ash was delivered to a central location from where it was loaded into a small commercial fertilizer spreader and transported to each plot location. The plots were 50’ x 100’, with two application strips on either long side. Rates were calculated for 10 and 20 tons/acre by using five catch pans spread across the spread path. Due to ash’s low density relative to commercial fertilizer, and spreader design, many passes were necessary to attain the rates of 7.5 and 15 ounces/square feet as measured and adjusted from the pan contents. These amounts yielded target rates of 20,000 and 40,000 lbs/acre.

Multiple passes had the negative result of destroying the standing dry grass sward in the tread paths in the center of each spread band; an unfortunate problem. Two exclusion cages (triangles, 65 square feet each) were placed in each test strip, with a fifth cage placed in adjacent untreated area. The remaining 50 x 100 plots were left open to grazing. Cages were secured against cattle impact, which proved difficult since ash had near immediate improvement in forage palatability, drawing livestock like magnets. One plot had to be abandoned due to being quickly destroyed by cattle. Protective electric fencing was necessary in another plot.

Soil and forage samples were taken in May and June 2013, dried, weighed and sent for analysis. Results are attached.

Research results and discussion:

As expected, ash encouraged legume growth and some plant species diversity, although with varying results. Drought conditions promoted invasive Medushead growth on some sites, thus effecting positive results. On other sites, lower application rates proved more agreeable to plant growth. In previous trials with normal rainfall, forage response was proportional to rates of ash application. According to veteran rangeland researchers, trials need to span at least five years to mitigate seasonal variations.

Previous trials used tilling incorporation in some locations and surface-spreading without tilling in other plots. Response rates seem to favor incorporation. This study purposely avoided tilling, which combined with low moisture, may account for slow plant uptake and response. However, ash remains viable and will gradually settle into the soil structure, thus acting like time-release nutrition.

Forage quality was slightly-to largely improved, according to ADF, NDF and protein analysis, as shown in attachments.

It is conceivable that improved forage production and optimism will lead to other environmental practices becoming accepted and more generally used. Division fencing, rotational grazing, stock watering development, riparian protection and many other practices are being unevenly implemented. Controlled grazing, the first order of improved range management, easily leads to observable changes in vegetation classes, quality and quantity, and any enhancement gained through ash usage. Since annual rangeland, with its invasive weeds, poor soil and low yield, has proven unable to return an investment in commercial fertilizer, the use of a free waste product is the only foreseeable amendment likely to begin a shift in soil and plant ecology and long-term agricultural beneficial impact.

Participation Summary

Research Outcomes

No research outcomes

Education and Outreach

Participation Summary:

Education and outreach methods and analyses:

We had three ranch workshops that were attended by a diverse audience, about 75 folks in all, including co-gen representatives, academics, environmental and rangeland advocacy groups, NRCS, RCD, UC Extension, ranchers and general public. The publication generated for these workshops (linked below) was distributed to over 150 persons and is still being requested.

Additionally, a slide presentation was given at the 2013 CalCAN Summit, attended by over 250 people. The slide show (below) featured overall ash usage on our ranch, with specific reference to this Western SARE project, addressing the theme “Building Resilience to Climate Change.”

Education and Outreach Outcomes

Recommendations for education and outreach:

Potential Contributions

With luck, this study will encourage more research and fly ash usage. Ash seems the best and only means of improving rangeland soils and production, where feasible. More information is needed, over a longer duration.

Future Recommendations

Further study is needed to build relationships between the co-generation industry and ranchers wishing to use fly ash as a soil amendment. Ash is the best viable source of nutrients, especially costly potassium and is capable of improving soil on rangeland scales, with benefits to the co-gen industry.

A business model also is needed that assumes ownership and environmental accountability for the ash and provides brokering services for both industry and agricultural use. Proving to ranchers that economic gains will offset initial application expenses and traditional risk anxiety also will be a formable task. Much future benefit depends on the bio-mass industry, which currently is not as stable as previously thought due to political inertia and plant conversion to inexpensive natural gas alternatives.

If a connection to carbon sequestration and other eco-services can be established as a result of ash usage on natural rangeland, further economic benefits will be assured.

Any opinions, findings, conclusions, or recommendations expressed in this publication are those of the author(s) and do not necessarily reflect the view of the U.S. Department of Agriculture or SARE.