Wood ash is leftover after wood fuel has been burned and is usually around 0.5-1% of the wood fuel volume. If managed correctly, it can be beneficial to apply this leftover ash to soil as it contains many nutrients and reduces the need for the disposal of ash in a landfill.
Ash is similar to agricultural lime as it is a good source of calcium and also contains other nutrients like potassium, phosphorus and magnesium and boron. Heavy metal concentrations (e.g. arsenic, cadmium, chromium, copper, lead, mercury, nickel and zinc) are generally low.
Before applying ash, both the ash itself and the on-site soil need to be tested for pH, nutrient and heavy metal levels. Once these levels are known, ash can be applied as appropriate and fertiliser levels reduced.