Classification Of Soils |

The most general level of classification in the USDA system of Soil Taxonomy is the Soil Order.

Soil orders are frequently defined by a single dominant characteristic affecting soils in that location, e.g., the prevalent vegetation (Alfisols, Mollisols), the type of parent material (Andisols, Vertisols), or the climate variables such as lack of precipitation (Aridisols).

All world soils are place into 10 orders.

1. Entisols:

Entisols have a very little or no profile development

Soils in desert belong to this classification.

The productivity of these soils varies with their location and properties.

With controlled water supply and proper fertilization, these soils can have good productivity.

They are good for vegetables, groundnut, citrus, wheat, paddy, etc.

2. Inceptisols:

These soils have better profile development than entisols but are less developed.

The horizons are formed mostly from alteration of the parent materials with accumulation of clay.

The productivity is limited due to poor drainage.

Found in humid regions.

3. Histosols:

These are organic soils (pleats and mucks) consisting of variable depths of accumulated plant remains in bogs, marshes and swamps that have developed under water saturated environment.

These are Highly rich in organic matter i.e. Org. C ranges from 12 to 18% in soils with low to more than 50% clay content.

4. Aridisols:

These are the soils found in arid or dry areas

They have a light colour

They are poor in organic matter and are not subjected to leaching

These are used for cultivation with irrigation

These are desert soils

5. Mellisols:

These are mostly found in grasslands having thick surface horizon of dark colour

These are dominated by divalent cations

They posses normal granular or crub structure

They do not harden on drying

They are productive with moderate to high fertilization

6. Vertisols:

These have a high content of clays that swell when wetted (more than 30%)

During the dry season, these soils on tract and give rise to deep cracks which disappear in the wet season or after irrigation

Found in sub humid or semi arid (Temperate to tropical) climates where temperatures are moderate to high

Good for crop production with fine texture which are plastic and sticky when wet and hard when dry.

Difficult to manage due to very little time for their proper preparation by tilling

Good for the production of cotton, millet, sorghum, wheat, paddy, etc.

7. Alfisols:

Develop in humid and sub humid climates (500 mm to 1300 mm rainfall) with gray to brown surface horizons

Soils are slightly too moderately acid and quite productive with good texture

Soils are frequently under forest vegetation

8.  Spodosols: Soils belong to forests with low content of bases, having coarse texture (sandy).

Found in humid climates where temperatures are low

The subsurface horizons have accumulation of organic matter and sesquioxide

9. Ultisols:

These are strongly acidic

These are normally forest soils with low content of bases

These are extensively weathered soils of tropical and subtropical climates

They respond to good management practices

They have clay of 1:1 type and give good crop production with adequate fertilization

10. Oxisols:

These mostly develope in tropical and subtropical climates

The subsurface horizons are high in clay and acid.

The soils are productive with supplements of ‘P’ micro-nutrients