The caliche –from its Spanish name, sometimes also named calcrete- is a hard, compact and extensive crust that is found in depth in the soil due to calcareous cementation. It is light marbled colour and it includes, in variable proportions and sizes depending on the areas, particles of clay, silt, sand and gravel already existing in the soil.
The caliche crust is always wide and ranges from about 10-15 cm to more than one meter thick. It is found roughly half a meter deep in the ground.

Caliche develops in soils of arid and sub-arid areas that receives or has received water from a higher level containing bicarbonate ions. As water evaporates from the soil, even more if plants contribute with evapo-transpiration and with selective absorption of the ions that rejects the most abundant ones, bicarbonate and calcium ions concentrates in the soil until they precipitate as calcium carbonate concrete on the existing particles. Over the time, impressive caliche crusts built. Some caliche crusts are fossil, the result from a past climate.
Despite its appearance and consistency of a rock, caliche is not properly a rock and should not be confused with the geological substrate, but rather an edaphic produce.

Caliche in the soil impacts the vegetation and the agriculture. The continuous, porous free crust of caliche is a barrier to infiltration of water; the water drains in surface increasing the arid conditions. Roots do not usually cross the caliche layer either -see the image- hence the soil thickness that is available for the plants is scarce. Caliche can be uprooted with powerful mechanical media to improve the agricultural prospects of a field, but the removal of the layer of caliche that provided consistency can trigger erosion and loss of the scarce but fertile soil that it maintained above.

Caliche in the soil is a frequent circumstance in sub-arid areas with limestone substrates present or nearby. It is found abundantly in the soils of Mediterranean climates, particularly on the Mediterranean slopes of the Iberian Peninsula from Camp de Tarragona to the south. The image of the soil profile showing caliche was obtained in one path in the area of Les Tàpies (Calders, Moianès).

[photo Jordi Badia]