This article throws light upon the top eight types of soils found in India. The soils are: 1. Red Soils 2. Laterite and Lateritic Soils 3. Alluvial Soils 4. Black Soils 5. Desert Soils 6. Forest and Hill Soils 7. Peaty and Marshy Soils 8. Terai Soils.
Type # 1. Red Soils:
Red soils occur mainly in the peninsular portion of India and along the east coast moving up to Assam in North-east and some are found in east central India. The soils are derived from crystalline granite and metamorphic rocks such as gneisses and schists.
Red (when ferric oxides occur as hematite) to yellow (when ferric oxides occur as its hydrated form) in colour which might be due to coatings of ferric oxides on the soil particles. The soils are shallow to very deep with well-drained conditions.
The pH of the soil varies from 6.3 to 8.0 and it is related with available P and iron oxide. These soils are wide variations in texture ranging from coarse sandy to loamy, excepting a few are clayey.
Morphologically, red soils are divided into two broad groups namely:
(i) Red loams characterized by argillaceous soil with a cloddy structure and the presence of concretionary materials and
(ii) Red earths-top soil is loose and friable but rich in secondary concretions as a consequence of sesquioxide type of clay.
Red soils are represented by red loamy soils and red sandy soils occur extensively in Tamil Nadu, Karnataka, Goa, Daman and Diu, Eastern parts of Andhra Pradesh, Chotanagpur and less extensively in south-east Maharashtra and Madhya Pradesh.
In the north and northeast, red soils occur in Mirzapur, Jhansi and Hamirpur districts of Uttar Pradesh, major part of San Thai Parganas in Jharkhand and Bihar, Birbhum districts of West Bengal and some parts of Bardhaman district, in Assam, Meghalaya, Mizoram, Tripura, Arunachal Pradesh and Manipur.
In general, red soils have low base saturation, poor in nutrient status, low cation exchange capacity (CEC) and low organic matter content having acidic in reaction. A distinctive feature of red soils is the high percentage of acid soluble Fe2O3 compared with AI2O3.
In the new US Comprehensive system, the soils may fit in the orders of Alfisols (Great groups:Haplustalfs, Rhodustalfs, Paleustalfs) and Ultisols (Great groups:Haplustults, Rhodustults, Ochraquults).
Type # 2. Laterite and Lateritic Soils:
Laterite is usually reddish or yellowish red in colour and often has a vesicular structure. The formation may be massive and firm or it may be in the form of loose aggregates of nodular ferruginous mass. The laterites are formed in tropical and sub-tropical climates having an alternate wet and dry season. The soils are rich in sesquioxides, devoid of bases and primary silicate minerals.
These are hard or capable of hardening when exposed to drying after wetting and turn as hard brick like materials which are used as bricks for construction of houses. It is composed of a mixture of the hydrated oxides of aluminium and iron with small amounts of manganese oxides, titania etc.
The soils are widely distributed and usually found in hill tops and plateau of Orissa, Maharashtra, Malabar hills, West Bengal, Kerala, Tamil Nadu and Assam.
Soils are deeply weathered, high clay content, low base and silica content, accumulation of sesquioxides and low in organic matter content. Kaolinite (1 : 1) is the dominant clay mineral of these soils and is formed due to neo-synthesis. With regards to fertility status of these soils, they are poor in most nutrients including micronutrients and toxic in aluminium and manganese.
These soils have been classified according to soil taxonomy in the orders of Oxisols and Ultisols. Most of the Laterite and Lateritic soils of India are classified as Plinthaquults, Plinthudults, Tropudults, Tropaqualfs and Plinthustalfs depending on the moisture content, base saturation etc.
Type # 3. Alluvial Soils:
Soils of alluvial origin are represented in the soil map under coastal alluvium, coastal sands, alluvial soils of the major rivers, calcareous alluvial soils, deltaic alluvium and ascalcareoussierozemic soils. These soils cover the largest area in the country and occupy an estimated area of 50 m ha in the Indo-Gangatic Plain and the Brahmaputra Valley.
Soils are widely distributed in most states of the country namely, Punjab, Haryana, Uttar Pradesh, Madhya Pradesh, Assam, Bihar West Bengal, Parts of Jharkhand, coastal regions of Orissa, Gujarat, Tamil Nadu, and Kerala. Alluvial soils of Indo-Gangetic Plains is of recent origin and derived from the deposition of erosion products brought and laid down by different river systems.
Another type of alluvium recognized is the coastal alluvium laid down by the sea currents. Characteristically, soils are variable in colour depending upon the source of parent material and calcareousness. Texture ranges from very coarse to fine with varying profile development (undeveloped to well-developed). Alluvial soils are rich in most plant nutrients excepting low in nitrogen and organic carbon contents.
Soils are usually neutral to alkaline in reaction but it may be acidic in reaction in high rainfall zones like in Assam (Annual rainfall > 2000 mm). The most recent (young alluvial) and sub-recent (old alluvial) soils are locally classified as “Khadar” and “Bhangar” respectively because of variations resulting from biological and climatic variations. In the genetic system, these soils were classified as Alluvial (Azonal) soils.
It may not hold good for all such soils as some of these have well developed profiles and may qualify the zonal soils.
In the New Comprehensive Classification System, alluvial soils may fit in the orders of Entisols (Great groups: Usti-Fluvents, Udi-Fluvents and Torri-Fluvents), Inceptisols (Great groups: Ustochrepts, Eutrochrepts), Alfisols (Great groups: Haplustalfs, Natrustalfs) and Aridisols (Great groups: Calciorthids, Camborthids, Salorthids).
Type # 4. Black Soils (Black Cotton Soils):
The soils of India also called Black Cotton or Regur soil constitute an important soil group and cover about one-third of the Deccan Peninsula extending for about 72 m ha between latitudes 15 to 26Â° north and longitudes 73 to 83Â° east. These soils are also called as Karail soil in the lower Gangetic basin in Uttar Pradesh and Bhal in Gujarat. In Bihar Tal lands also exhibit the properties of black soils.
Typical soils derived from the Deccan trap and developed under semi-arid and sub-humid climatic conditions under grass vegetation’s are known as black cotton soils. It is smectitic clay rich, self-mulching black soils with swell-shrink properties.
These soils are commonly found in central, western and southern states of India including Maharashtra, Western parts of Madhya Pradesh, Gujarat and some parts of Andhra Pradesh, Karnataka and Tamil Nadu.
Black soils are characterized by a dark grey to black colour, high clay content, and neutral to slightly alkaline in reaction. Typical black cotton soils have developed on basaltic rocks under varying climatic conditions. These soils are formed from Deccan basalt trap rocks in situ or on the transported parent materials.
Two kinds of parent rocks are involved for the formation of black soils viz:
(i) Deccan and Rajmahal trapsâ€”volcanic rocks such as basalt and other basic metamorphic rock sand
(ii) Granite, gneisses and schistsâ€”lime and soda lime feldspars which are basic in characters.
During the formation of black soils, the presence of high proportion of alkaline earth’s in the weathering process and impeded drainage conditions of the parent materials are of great importance. According to soil taxonomy, the medium and deep black soils are grouped into Vertisols and the characteristics are almost similar to that order.
However, the shallow black soils are also included in the order of Entisols and Inceptisols depending upon the profile development. Soils have high coefficient of expansion and contraction involving churning.
The process of churning leads to the development of typical features as follows:
Wide and deep cracks
Closely intersecting slickensides
Soils have narrow workable moisture, low infiltration rate, poor drainage and moisture stress. It has poor to high fertility status, however, poor in organic carbon, low N, S, and P contents. Under irrigated conditions the productivity of black soils is high.
Because of high water holding capacity, these soils are suitable for rainfed agriculture. There are some other soils found in India namely, desert soils, forest and foot hill soils, salt affected soils, acid sulphate soils etc. whose brief descriptions are given below:
Type # 5. Desert Soils:
The desert tract of Rajasthan stretches from the west of the Aravallis to the basin of the Indus in the west and from the southern confines of the Punjab plains covering an area of 29 m ha. The soils develop in hot desertic region and these are found in Rajasthan, southern parts of Haryana and Punjab and northern parts of Gujarat.
The rainfall ranges from 50 to less than 10 cm. The temperature is very high throughout the year; however, the average temperature of surface soil is about 35Â°C. A maximum soil temperature has been recorded during summer months as 50-60Â°C. Precipitations in a well-defined period make it quite effective for biological activity.
Organic matter content of the soils is very low. The sand constituting sand dunes might have been transported from the Rann and Lower Indus basin. In plains, these soils are mostly derived from alluvium and are pale brown to yellow brown, fine sandy to loamy fine sand and mostly structure less. Accumulation of alkaline earth carbonates is common feature for most soils.
The pH of these soils usually ranges from 8.0-8.8. The presence of Na-clay and natric horizon makes the soils susceptible to dispersion and less permeable. However, soils contain phosphate and nitrate which make the soil fertile and it contains illitic clay predominantly with small amounts of kaolinite, chlorite and vermiculite. Typical desert soils have been classified in the order Aridisols and others in Entisols.
Type # 6. Forest and Hill Soils:
The total forest area in India is estimated more than 75 m ha which occupies 18% of the total geographical area.
In India, the total major forest areas are covered by tropical deciduous, coniferous and tropical evergreen forests and found in Himachal Pradesh, Jammu & Kashmir, Uttaranchal, Uttar Pradesh, Nagaland, Assam, Meghalaya, Odisha, Arunachal Pradesh, Madhya Pradesh, Kerala, Andaman & Nicobar Islands, Mizoram and Manipur.
The profile development in forest and hill soils is usually controlled by variation in climate and altitude, and kind of plant species etc. The major soils under forest and hill soils are brown forest, podzolic (in The Himalayas), Red and Lateritic soils (in the Deccan Plateau).
The Himalayas soils are formed under temperate climatic conditions with coniferous forests and the dominant rocks are sedimentary, igneous or metamorphic. The Deccan Plateau soils are formed from igneous and metamorphic rocks under tropical climatic conditions with deciduous forests.
There are two kinds of soil formation in forest soils namely:
(i) Soils formed under acidic conditions in the presence of acid humus and low base saturation
(ii) Soils formed under slightly acidic to neutral and high base saturation conditions. The podzolic forest soils are developed under coniferous forest vegetations resulting from the leaching of bases and translocation of sesquioxides.
The brown forest soils are developed on sandstones, limestone or colluviums under slightly acidic to neutral reaction and in humid climatic environments and pinus or mixed vegetation conditions.
In-spite of high accumulation of organic matter under high rainfall, cool climate and acidic conditions in brown forest soils, there is no release of Al and Fe due to acid hydrolysis breakdown of soil material and their interactions with humus constituents. Brown forest soils have moderate CEC (15-25 Cmol (p+/kg) and high biological activity.
Type # 7. Peaty and Marshy Soils:
Peat soils occur in humid regions containing sufficient amount of soluble salts and organic matter. Such saline peat soils are called as Kari soils (remain submerged during the monsoon period) and are found in Kerala.
The soils are black in colour having fine texture and an accumulation of ferrous and aluminium sulphates, iron pyrite in tidal swamp areas, when drained the pyrite is oxidized and sulphuric acid is formed resulting in strong acidic in reaction (pH< 4.0).
Such soils are very frequently called as cat clays or acid sulphate soils. However, Marshy soils of this type; occur in coastal areas of Odisha and Sundarban areas of West Bengal, and south-east coast of Tamil Nadu. The soils are very problematic because of the presence of pyrite which produces sulphuric acid on oxidation.
When such soils are submerged, then it is useful for the cultivation of rice. The marshy soils are usually found in depressions caused by dried lakes in alluvial and coastal plain areas.
Type # 8. Terai Soils:
Terai soils indicate soils which have high moisture regime and high water table. It remains moist in most part of the year. It is foot hill soils and mostly found in foot hills of the Himalayas, Jammu & Kashmir; Bihar and West Bengal.
In West Bengal, Terai soils occupy a major rice growing areas which include Jalpaiguri, Coochbehar and some parts of Darjeeling districts. These soils are brought down by Teesta, Torsha and Jaldhaka rivers from high mountains and deposits are chiefly sands, raw humus type, deep black to grey black in colour.
These soils are acidic (pH 4.5-5.8) with very poor base saturation and low available nutrient contents. Drainage facilities are very poor. However, the amount of organic matter content is high which exhibit a special significance in horizon differentiation and is predominated by dark coloured surface horizon and development of dark colour in the cambic horizon.
Tarai soils are fertile and productive having proper drainage. These soils having mollicepipedons and fall in the order mollisols.