Calcisols are soil with significant accumulation of secondary calcium carbonates, generally developed in dry areas. Soils belonging to this Reference Soil Group are common on calcareous parent material in regions with distinct dry seasons, as well as in dry areas where carbonate-rich groundwater comes near the surface.
The total Calcisol area amounts to some 10 million km2, nearly all of it in the arid and semi-arid (sub)tropics of both hemispheres.
Many Calcisols are old soils if counted in years but their development was slowed down by recurrent periods of drought in which such important soil forming processes as chemical weathering, accumulation of organic matter and translocation of clay came to a virtual standstill. However, most Calcisols have substantial movement and accumulation of calcium-carbonate within the soil profile. The precipitation may occur as pseudomycelium (root channels filled with fine calcite), nodules or even in continuous layers of soft or hard lime (calcrete).
Most Calcisols have a thin (=<10 cm) brown or pale brown surface horizon over a slightly darker subsurface horizon and/or a yellowish brown subsoil that is speckled with white calcite mottles. The organic matter content of the surface soil is low, in line with the sparse vegetation and rapid decomposition of vegetal debris.
Most Calcisols have a medium or fine texture and good water holding properties. Slaking and crust formation may hinder the infiltration of rain and irrigation water, particularly where surface soils are silty. Surface run-off over the bare soil causes sheet wash and gully erosion and, in places, exposure of a petrocalcic horizon.
Vast areas of ‘natural’ Calcisols occur under shrubs, grasses and herbs and are used for extensive grazing. Drought-tolerant crops such as sunflower might be grown rain-fed, preferably after one or a few fallow years, but Calcisols reach their full productive capacity only when carefully irrigated.
Formerly Calcisols were internationally known as Desert Soil and Takyrs.
Calcisols cover less than 10,000 km2 land surface of Europe. Calcisols occur in two countries, being dominant on the islands of Malta and covering about 1.7 of total land area of Spain.