Organic ash is the residue left after organic material, such as wood or leaves, is burned. Other terms used to describe organic ash include biomass ash, plant ash, and natural ash. Biomass ash is frequently used to describe ash generated from burning crops and agricultural waste. Plant ash refers specifically to ash generated from the burning of plants, such as grasses and trees. Natural ash is used to describe ash generated from natural sources, such as volcanic eruptions. Regardless of the term used, organic ash is widely used as a fertilizer due to its high nutrient content, including potassium, magnesium, and phosphorus.