Abstract

Andisols have unusual, and often extraordinary, properties not commonly found in other types of soils. This chapter provides an overview of the distribution and characteristics of Andisols, the potential and mechanisms for carbon sequestration, the suitability and constraints of these soils for agricultural production, and their susceptibility to threats to soil health. Andisols occur in many climatic regions and are primarily formed from volcanic ejecta, with unique characteristics due to the presence of short-range order minerals (e.g., allophane, imogolite, and ferrihydrite) and metal-organic complexes. Collectively, these constituents are referred to as active aluminum/iron (Al/Fe), and greatly influence the physical, chemical, and biological properties of Andisols. Active Al/Fe phases contribute significantly to the accumulation of organic carbon through chemical stabilization and physical protection mechanisms. While their exceptional physical properties (e.g., low bulk density, high porosity, and high water holding capacity) are generally suitable for agricultural production, certain Andisols may have constraints associated with the presence of cemented layers, changes in soil structure upon drying, and water repellency. Inherent fertility also varies in Andisols, and these soils may require corrective actions to overcome production limitations associated with nutrient deficiencies, acidity, aluminum toxicity, and/or phosphorus sorption. While these soils can be resilient, Andisols may also be susceptible to degradation due to land use change, poor management, and other threats to soil health.