calcisols

Calcisols are a soil type defined in the World Reference Base for Soil Resources (WRB) as soils in which calcium carbonate has accumulated in a subsurface horizon, known as a calcic horizon. This calcic horizon forms through secondary processes that move calcium carbonate downward from the upper horizons, usually under conditions where leaching is limited and evaporation concentrates carbonates in deeper layers.

Formation and horizons: Calcisols develop on calcareous or lime-rich parent materials in semi-arid to arid climates. The overlying horizons may be relatively poor in organic matter and clay, while a distinct calcic horizon lies beneath, often at moderate depths. In some environments, the carbonate-rich layer becomes cemented, creating a petrocalcic or duric horizon. The surface may appear light-colored or grayish due to reduced leaching and limited organic matter.

Properties and limitations: Calcisols commonly have neutral to alkaline pH due to carbonate content, low natural fertility, and limited nutrient-holding capacity in relation to clay-rich soils. They are typically shallow in places where a hard caliche layer forms, and their structure ranges from sandy to loamy. The presence of carbonates can impede root growth and water movement, influencing vegetation and land use.

Distribution and significance: Calcisols are found in arid and semi-arid regions worldwide, including parts of North Africa, the Middle East, Central Asia, western North America, and Australia. They are often associated with grazing lands and are generally less suitable for intensive cropping unless managed with irrigation, drainage, and soil amendments. They are an important component of regional soil mosaics and land-use planning.