ANDOSOL

one of the 30 soil groups in the classification system of the Food and Agriculture Organization (FAO). Andosols are highly porous, dark-coloured soils developed from parent material of volcanic origin, such as volcanic ash, tuff, and pumice. They are found from Iceland to Indonesia, but they typically occur in wooded highland areas of the continental lands bordering the Pacific Ocean. Their worldwide extent is estimated at less than 1 percent of the total soil area on Earth. Andosols have high aluminum content, and their reactions with inorganic phosphate render the phosphate essentially insoluble and unavailable for uptake by plants. Although the soils have excellent water-holding and nutrient capacity (unless leached extensively), their strong reaction with phosphate makes agriculture without fertilizing problematic. Andosols are similar to the Andisol order of the U.S. Soil Taxonomy.