BRIAN PAIGE
Using RECEIVES Wood Ash BEACON as a Soil AWARD Amendment
BRIAN PAIGE
Using RECEIVES Wood Ash BEACON as a Soil AWARD Amendment
By Sam Corcoran, UMass Extension Soil and Plant Nutrient Testing Lab Manager Artie Siller, UMass Extension Soil Health Educator wood ash generated by a home or farm analyzed by a fertilizer lab. If using non-commercial ash sources, apply ash conservatively and use routine soil tests to track the effect.
Wood ash can have long-term effects on the soil, and large, infrequent applications are often most practical. That said, too much wood ash can lead to excessively high soil pH and soil potassium levels. Wood ash generally produces a smaller rise in pH than the same amount of lime due to the differences in CCE. However, the liming effect of wood ash can be faster than traditional lime and may temporarily raise pH higher than intended. Due to the high pH of wood ash, it also should not be applied with ammonium or urea fertilizers since it can increase the amount of nitrogen volatilization.
Wood ash can be used to improve soil health, including fertility. Using wood ash for fertilizer also keeps it out of landfills. The term“ wood ash” refers to ash from smallscale wood burners, paper and lumber mills, and power plants. All of these materials can be used as liming agents and potassium fertilizer, though the source of the wood ash can impact the properties of the material.
Wood ash is mostly made of minerals bound to hydrogen, oxygen, and carbon, as well as small amounts of residual organic matter. The liming effect, nutrient availability, carbon content, and organic matter associated with ash materials are highly influenced by how thoroughly the material is incinerated. Incomplete incineration can also lead to too much charcoal – a form of carbon residue – in the ash, which can tie up soil nitrogen and phosphorus after ash is applied. For this reason, avoid using partially burnt ash. In a thoroughly incinerated wood ash product, organic matter, carbon, and nitrogen are present in negligible amounts.
The source of wood ash material, like hardwoods versus softwoods, or stove ashes versus paper mill ashes, results in large variation. For example, the liming value of wood ash, measured by the calcium carbonate equivalent( CCE), ranges from( 20-90 %). Lime recommendations from a soil lab assume a CCE of 100 %. Thus, more wood ash is required to achieve the same liming effects as quality agricultural lime. Similarly, the amounts of calcium( 20-35 %), potassium( 1-15 %), and magnesium( 1-9 %) are quite variable. Commercial ash products are required to provide guaranteed analysis of the CCE and nutrient content, just like conventional fertilizer and lime products. However, it is often impractical to have small-scale
If users do not desire increases to both pH and potassium, then other soil amendments should be used in place of wood ash( e. g. limestone or potassium fertilizer such as potash). Wood ash use can also result in increases in minor elements like boron and manganese. Routine soil tests should be used to track these changes and avoid excessive accumulation of trace mineral levels over long periods.
Applying Ash General best practices for using wood ash as a lime and fertilizer amendment are as follows:
Base wood ash application on soil test recommendations for lime and potash.
Account for the CCE difference of wood ash versus lime. View our fact sheet for more on this math.
Apply an annual, average maximum of 45 lbs / 1000 square feet( 2000 lbs / acre). Only apply a larger amount if wood ash is not applied every year. It’ s best to limit each application to no more than 4500 lbs / acre.
For commercial ash, use the calcium carbonate equivalent( CCE) and soluble potash content from the supplier to determine application rate.
For ash produced on-site, use generic ash content( see below) to calculate application rates.
Do not use fly ash as a soil amendment. Fly ash is the last bit of materials filtered out of smoke in commercial incinerators and has a higher metal content than other ash products.
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MALP Newsline | Spring 2026 13