andisol

Andisol is a soil order in the USDA soil taxonomy that refers to soils formed in volcanic ash or tephra. In the World Reference Base for Soil Resources, the equivalent group is named Andosols. These soils are characterized by the presence of amorphous or poorly crystalline minerals, especially allophane and imogolite, which strongly influence their chemical and physical properties.

Formation and properties: Andisols form rapidly in recently deposited volcanic ash and tend to be relatively young soils with distinctive horizons that may be underdeveloped. They typically have high porosity and water-holding capacity, and often exhibit low bulk density. The amorphous minerals give Andisols high surface area and reactivity, contributing to substantial cation exchange capacity and pronounced phosphorus fixation. They commonly display acidic to neutral pH, though liming can modify this in cultivated areas. Iron and aluminum oxides are present in forms that influence nutrient dynamics.

Management and use: The high phosphorus fixation of Andisols can limit P availability for crops, requiring carefully managed phosphorus fertilization. Their fertility can be excellent where nutrients are supplied and drainage is appropriate, but management must address acidity, P fixation, and potential micronutrient limitations. Organic matter management and soil structure improvement are important for sustaining productivity.

Distribution and occurrence: Andisols occur in volcanic regions worldwide, including areas around the Pacific Ring of Fire, such as Japan, Indonesia, and the Andes, as well as parts of Central America, Iceland, and East Africa. Their unique properties make them both productive agricultural soils in the right management and challenging soils where nutrient availability is limiting.