The following document is intended to outline a procedure for guiding land application of wood ash as a lime substitute on agricultural lands. It details one method that should be suitable to manufacturers, suppliers, dealers, and landowners. While these recommendations carry no regulatory authority in Georgia, they have been reviewed and accepted by the Environmental Protection Division of the Department of Natural Resources and the Georgia Department of Agriculture. Although these procedures do not hold any regulatory authority, land application of the wood ash should not have any adverse environmental effects or result in regulatory activity if these conditions are met. These recommendations are intended to facilitate the process of land applying wood ash to take full advantage of both the liming and nutrient values inherit to wood ash as well as benefiting the State's landfills through a reduction of inputs.
Wood ash is the ash derived from the combustion of bark, wood, sawdust, leaves, woody debris, pulp, sludge from pulp and paper wastewater treatment systems, and unbleached wood fiber. Except for the auxiliary use of gas or oil, it does not include ash from mixed fuels or other products. While mixed ashes and other residuals from pulp and paper manufacturers also have value as a soil amendment and lime substitute, this document only considers wood ash as defined above. The University of Georgia, in cooperation with several other organizations, is currently studying many of these other by-products. If these studies indicate that it is appropriate, similar procedures will be recommended for these products. These procedures do not apply to any materials registered with the Georgia Department of Agriculture and do not replace or circumvent any State regulations.
Any supplier wishing to make wood ash available to the public for land application should first test the product. Testing should include an analysis for nitrogen (N), phosphorus (P), potassium (K), sodium (Na), calcium (Ca), magnesium (Mg), lime equivalency (CCE), and the nine metals outlined in EPA regulations for application of "exceptional quality" municipal sludge (40 CFR part 503.13) and listed in Table 1 of this document. All analysis should be conducted using EPA approved procedures and laboratories. If any of the metal concentrations exceed the pollutant concentrations shown in Table 1, the wood ash should not be land applied as outlined in this document. Testing of the ash should be accomplished using weekly composite samples (2 to 3 samples per day over five days) twice per year. In addition, the supplier should also retest the ash after any significant process modification or changes in raw material inputs. The corporation should maintain records of all test results for at least three years and these records should be provided upon request to the county Extension office, land owner, or commercial applicator for the purpose of calculating application rates.
The amount of wood ash that may be land applied to a particular area should be based on the desired soil pH and the nutrient loadings for the crop. Each land owner/farm operator who wishes to receive bulk wood ash should test the soil on each site prior to each application of wood ash. For use as a lime substitute, application rates should be calculated from liming rate recommendations, the soil test pH for the site and the lime equivalency (CCE) of the ash. The "Soil Testing Handbook" of the University of Georgia Extension Service or laboratory recommendations should be used to determine the proper liming rates. While the application rates should primarily depend on the lime requirements to bring the soil to the optimum pH, the nutrient contribution of the ash may also be calculated so that fertilizer inputs can be reduced where appropriate. An estimate of the total amount of wood ash required for each location based on the farmer's available land base should also be calculated using the application rate. It will be the responsibility of the land owner/farm operator to adhere to these loading rates for the application of this product. All soil testing and application rate calculations can be made available through The University of Georgia Cooperative Extension Service, however, any qualified individuals may provide these services.
Before providing wood ash to any farmer/landowner, the wood ash supplier should insure that the following requirements have been satisfied: 1) the wood ash has been tested and the test results did not exceed the allowable metal concentrations. 2) at each application site, soil testing has been performed and the optimum application rate has been calculated. 3) Each land owner has received a copy of The University of Georgia Cooperative Extension Service Bulletin on Best Management Practices for Wood Ash Used as an Agricultural Soil Amendment. 4) Each receiver of ash has completed and returned to the supplier an acceptance form stating that they agree to take ownership, control, and responsibility for this material as provided. To insure that these conditions are met, the supplier may wish to keep records of each transaction. These records should include the name and address of the person receiving the wood ash, the amount of ash provided, and the date it was provided.
Table 1. Pollutant concentrations from 40 CFR part 503.13 Pollutant Pollutant Concentration
Arsenic 41 Cadmium 39 Copper 1500 Lead 300 Mercury 17 Nickel 420 Selenium 100 Zinc 2800 * Dry weight basis, 1 mg/kg= 1 ppm.
Note: These are the pollutant concentrations from the EPA regulations for land application of municipal sludge. They are being used as a guideline in this document. The wood ash should have concentrations below these pollutant levels, however, they do not need to meet all of the conditions outlined in 40 CFR part 503.13. If the concentration of any metal exceeds these concentrations then the wood ash should not be land applied.
- Dr. Mark Risse, University of Georgia Cooperative Extension Service, Agricultural Pollution Prevention Specialist
- Dr. Larry Morris, University of Georgia School of Forest Resources
- Dr. Glen Harris, University of Georgia Cooperative Extension Service, Agronomy Specialist
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