Wood ash
Wood ash is the mineral-rich residue left when wood burns, composed mainly of calcium compounds with potassium, magnesium, and other minerals.
Liming (soil): The application of alkaline materials to soil to reduce acidity and supply calcium or magnesium. Wood ash can raise soil pH, though its variable composition makes application rates difficult to predict.
Combustion: A chemical reaction in which a fuel reacts rapidly with an oxidizer, releasing heat and often light. Burning drives off most wood carbon and hydrogen as gases, leaving its nonvolatile mineral fraction.
Soil pH: A measure of hydrogen-ion activity in soil solution, commonly used to describe soil acidity or alkalinity. The alkaline compounds in wood ash can increase soil pH and harm plants if applied excessively.
Fly ash: Fine particulate residue carried from a combustion chamber and captured from flue gases, especially at coal-fired plants. Unlike wood ash, fly ash usually comes from coal combustion and has distinct industrial chemistry and regulation.
Potash: Potassium-rich material used chiefly in fertilizers and historically obtained from plant ashes. Leached wood ash was a traditional source of potassium salts used to make potash.
Wood: The structural tissue of trees and other woody plants, composed mainly of cellulose, hemicellulose, and lignin. The mineral content of the original wood sets an upper bound on the ash’s inorganic material.
Soil salinity: The accumulation of soluble salts in soil at levels that can restrict plant growth. Repeated or heavy ash application can add soluble salts as well as nutrients.
Bottom ash: Coarser combustion residue that settles at the bottom of a furnace or boiler. Wood ash can include both fine and coarse residues, while bottom ash names a particle and collection fraction.
Soap: A cleaning substance made from fatty acids or fats reacted with an alkali. Ash-derived lye supplied alkali for traditional soap-making.
Calcium carbonate: A calcium salt found in minerals such as calcite and formed in many biological and geological settings. Calcium compounds dominate many wood ashes, and carbonate can form as ash cools and absorbs carbon dioxide.