LIMESTONE SOIL: CHARACTERISTICS, COMPOSITION, FORMATION, STRUCTURE - BIOLOGY - 2025

The calcareous soils or calcareous are those with a high content of calcium carbonate. They are mineral soils whose formation has been conditioned by the climate. They have been classified as calcisols and are characterized by secondary accumulation of carbonates and high silt content.

The presence of high levels of calcium carbonate determines a basic pH. They have low organic matter content and generally occur in arid or semi-arid areas around the globe. They also occur in lake areas with a high contribution of calcium carbonate from gastropod and bivalve shells.

Calcareous soil profile in Seven Sisters Park (United Kingdom). Nigel Chadwick

They are suitable soils for agricultural activities, as long as they have adequate fertilization and irrigation. Among the most common crops we have the sunflower, the vine and the olive trees.

characteristics

Parent material

Calcareous soils originate associated with parental material rich in calcium carbonate in arid or semi-arid areas. This includes alluvial, colluvial, or aeolian deposition of calcareous material.

It can come from the erosion of calcareous sedimentary rocks or from recent depositions from drying lake areas.

Physicochemical characteristics

They are medium to fine textured soils with good moisture retention. In some cases they may have a high proportion of large diameter rock particles.

They normally show high silt content. They can form superficial crusts making it difficult to percolate. They have between 1 and 2% organic matter. The calcium carbonate content is equal to or greater than 25%.

The sand and clay content are variable, depending on whether they are associated with other types of soils. In association with vertisols they will have a higher content of clays. With sandy ones the sand content will be higher.

Morphological characteristics

Calcareous soils or calcisols generally have a very thin surface horizon (less than 10 cm) of brown to light brown color. Then follows a somewhat darker or yellowish-brown horizon dotted with white specks of calcite.

At a greater depth, a block structure with larger aggregates may appear, often reddish in color or made up of parent material.

Hydrological characteristics

They are well-drained soils, conditioned by the physiography where they are normally found and their texture. If a calcareous soil is in a depression, it is susceptible to a high accumulation of salts.

This saline soil condition is normally classified in a category other than calcisol (Example: Solonchaks).

Composition

Calcareous soils can be made up of different types of rocks that are rich in calcium. Depending on the rocks present, various minerals associated with the soil can be found.

The vast majority of these soils are composed of limestone rocks that have a high content of calcite and aragonite. When basalts are present, an abundance of iron and magnesium is observed.

The sandstones present in some limestone soils contain quartz and feldepastes. While soils with schists can present garnet, muscovite and graphite.

Training

In the horizon A (or vertical washing zone of the uppermost layer of the soil) there is a higher pressure of CO ₂ than in the air above the soil, due to radical activity and microbial respiration.

This causes the dissolution of calcite (CaCO ₃) in the water. Ca _{2 + -} ions and HCO ₃ are carried by water towards lower horizons. As the water descends, it evaporates and the pressure of CO ₂ decreases. Under these conditions, calcite precipitates and forms the layer or aggregates of lime.

The redistribution of calcium carbonate, like other mineral elements, is an important horizon differentiation mechanism in dry zone soils.

Soluble salts can accumulate in shallow areas. The presence of groundwater near the soil surface also conditions these processes.

Structure

Some of these soils have been formed for many years, but do not have a great edaphological development, because they are subjected to long recurrent periods of drought, which limits most of the most important processes in soil formation.

Three horizons can generally occur. The most superficial horizon (A) is poorly structured and has a low calcium content.

Later, an accumulation horizon B is presented, where it can be visible due to the large accumulation of calcium. Below this, a C horizon made up of the parent material is present.

The structure of horizon B defines the types of limestone soils that can occur. According to the way this profile differs, we have:

Soils with diffuse Horizon B

The calcium content is only 10% higher than in the other two horizons. The depth can be 50-100 cm, and calcium accumulates in the form of fine particles.

When studying the soil profile, it is difficult to recognize this accumulation horizon, since there are no great color variations with the other horizons. Therefore, it is necessary to wait for the chemical analysis to certify its presence.

Soils with moderately differentiated Horizon B

In this case, the horizon can be differentiated in the profile. The accumulation of calcium carbonate is between 50-60% and the form in which it appears can be in nodules or fine particles.

The depth of this horizon can go between 20-100 cm. Generally the transition between horizon A and B is somewhat diffuse.

Soils with a markedly differentiated B horizon (Petrocalcic horizon)

When the soil profile is studied, the accumulation horizon can be clearly differentiated. In this there are large amounts of calcium carbonate and other minerals that form a hardened layer.

The depth of this horizon can range from 10 cm to two meters. The color is quite light and the calcium scale can come in different shapes.

The petrocalcic horizon originates under conditions of high temperature and high pH. This favors the dissolution of silica from feldspars, ferromagnesian minerals, among others. Likewise, a high translocation of calcite occurs.

Location in the world

Calcisols or calcareous soils are found in a wide range of landforms, including foothills, lake bottoms, lacustrine drying grounds, terraces, and alluvial fans or cones.

Making an estimate, the area occupied by calcisols is approximately 1 billion hectares worldwide. Some authors point out that 30% of the planet's soils are calcareous. Most are located in arid and semi-arid areas of the tropics and subtropics.

One of the areas where they are most abundant is the Mediterranean, due to the predominance of arid climates. They are also frequent in Egypt, Syria, Iran, Iraq, Jordan and Turkey among others.

In America they are not very common, occupying less than 2% of its surface. We can find them in northern Mexico and northern Argentina. In a very localized way, they occur on the coast of Venezuela and some areas of Chile.

Crops

Most calcisols are well drained, but they are not very fertile and have moisture only during the rainy season. This determines its main limitations for agriculture. If there is a petrocalcic horizon, subsoiling work is required (breaking this layer with deep plowing or subsoiling).

If calcareous soils are irrigated, drained and fertilized, they can be highly productive in a wide variety of crops. In mountainous areas, calcisols are used primarily for low-volume grazing of cows, sheep, and goats.

Calcareous soils are suitable for drought tolerant crops such as sunflower. In the Mediterranean area, irrigated winter wheat, melon and cotton are grown in large areas of calcisols.

They are also suitable for the production of citrus, peanuts, soybeans, olives and sorghum. With proper irrigation and fertilization, various species of vegetables can be produced.

In viticulture, it is pointed out that the grapes grown in these soils provide full-bodied, alcoholic, complex wines, very good for aging.

References

1. Chen Y and P Barak (1982) Iron nutrition of plants in calcareous soils. Advances in Agronomy 35: 217-240.
2. Driessen P, J Deckers and F Nachtergaele (2001) Lecture Notes on the major soils of the world. Food and Agriculture Organization of the United Nations (FAO). Rome Italy. 334 pp.
3. López-Bermúdez F, LJ Alias-Pérez, J Martínez-Fernández, MA Romero-Díaz and P Marín-Sanleandro. (1991) Runoff and soil losses in petric calcisol under a semi-arid Mediterranean environment. Quaternary and Geomorphology 5: 77-89.
4. Porta J, M López-Acevedo and C Roquero. (2003). Edaphology for agriculture and the environment. 3 Ed. Ediciones Mundi Prensa, SA 917 p.
5. Reardon EJ, GB Allison and P Fritz (1979). Seasonal chemical and isotopic variations of soil CO ₂ at Trout Creek, Ontario. Journal of Hydrology 43: 355-371.