Factors that affect the chemical composition of wood ash, and the potential implications of recycling wood ash have been extensively reviewed:

Use of ash in forestry ^(PDF-526K)

This review concludes that:

• Low level ash applications have been successfully used for fertilising nutrient-poor forest soils
• Short and long-term field experimentation confirms the importance of soil type in determining the effects of wood ash application
• Problems associated with ash application in forests are not its heavy metal content, but its high calcium content
• A high calcium content of wood ash raises soil pH, increases microbial populations and the potential mineralisation of nitrogen
• Heavy metals can be largely removed or reduced at source, but increased soil pH could change the ecology and nature of forest ecosystems over long time periods.

This study confirmed the complexity of wood ash application to forest soils and the need for further research and long-term experimentation.

Further research

The use of wood ash as a soil additive and the effects of wood ash application to a range of soils and tree species will be studied.

The application of wood ash following whole tree harvesting or brash removal and also for nutrient replacement into poor forest soils is considered as an important potential research area.

In addition, there has been little interest to date in using sewage sludge and compost or green waste as fertilisers in forests. However, the ban on sea dumping and the restrictions on application to agricultural land and landfill may increase the interest and demand from water supply and waste companies.