Soil Classification: Types of Soils

April 3, 2016 April 3, 2016

Soil classification based on observable soil properties actually seen in the field is known as soil taxonomy. There are a number of soil classifications presented by the experts of soil science. The major types of the soils have been discussed here:

Oxisols

These soils develop in the hot and humid climates of the equatorial region. These soils are called oxisols because they have distinctive horizon with a mixture of iron and aluminium oxides. Related vegetation is the luxuriant and diverse tropical and equatorial rain forest. Typical are red-dish and yellowish from the iron and aluminium oxides left behind, with a weathered clay-like texture. In fact, these are the lateritic soils in which the leaching process is very strong. The Laterite can be quarried in blocks and used as building material. They are traditionally being used for shifting cultivation. When oxisols are disturbed, soil loss can exceed a thousand tones per sq km per year.

The regions dominated by oxisols by oxisols and rain forests are attracting the much worldwide environmental attention.

Aridisols (desert soils)

The largest single soil order occurs in dry regions of the world. These soils occupy nearly 19 per cent of the earth’s land surface. Pale and light near the surface, deficit in moisture. Lack in organic matter. Salinisation is the main problem of these soils. Salinisation complicates farming in Aridisols.

Mollisols (grassland soils)

They are most productive soils of the earth. They are rich in humus content. They have dark –colored surface.
Mollisols are soft, even when dry, with granular pads, loosely arranged when dry. These humus rich organic soils are high in basic cations and have high fertility.
Soils of the steppes and prairies of the world belong to this group. These soils are being utilized for large-scale commercial grain farming and grazing.
The process of calcification is very strong in these soils. When cemented or hardened, these deposits are called calche or kankar.

Alfisols (moderately weathered forest soils)

These are the most widespread of the soils orders, extending form near the equator to high latitudes. Pale, grayish brown to reddish in colour and are considered moist versions of Mollisols soil group.
Alfisols have moderate-to-high reserves of basic cations and are fertile. How-ever, their productivity depends on moisture and temperature. They are supplemented by the moderate application of lime and other chemical fertilizers. Some of the best agricultural farms of usa have this type of soil.

Ultiosols

These highly weathered forest soil are found in the temperature climates. These soils tend to be reddish in colour because of residual iron and aluminium oxides in the a horizon.
The increased precipitation in ultisol regions means greater mineral alteration, more leaching, and therefore, a lower level of fertility.
Fertility is further reduced by certain agricultural practices and the effect of soil damaging crops such as cotton and tobacco. These soils need substantial management.

Spodosols (coniferous forest soils)

Found in the humid continental mild summer climates. Their distribution is found in North America and Eurasia.
They are not found in the southern hemisphere.
Spodosols lack in humus and clay in the horizons.
The leaves of the conifers add acidity in soil. Their colour is ash gray and they are also known as podozal soils. These are not very fertile soils.
To enhance the fertility, the application of lime required.

Entisols ( recent, underdeveloped soils)

Usually young or underdeveloped.
Lack vertical development of horizons.
These are less fertile soils. The sand dunes ergs outwash glacial plains, and the poorly drained tundra, tidal mud flats, etc. are the examples of Entisols.

Inceptisols (weakly developed soils)

These soils are inherently infertile.
They are usually the weakly developed young soil though they are more developed than entisols.
They include the soils of most of the arctic tundra and outwash moraines.

Andisols ( volcanic parent materials)

The term andisols has been derived from volcanic ash and glass.
Highly fertile and have a high water holding capacity.
These soils occupy relatively smaller area, especially around the volcanic ring of fire in the pacific rim. Examples are the fertile soils of Hawaii that produce sugarcane and pineapple as important cash crops.

Vertisols (expandable clay soils)

Composed of more than 30 per cent clays.
Vertisol clays are black when wet and become iron hard when dry.
When drying, Vertisols crack and the cracks widen and deepen as the soil dries ; this produces cracks 2-3 cm wide. These are productive soils .
The regur soils of India are an example of vertisols.