The Indian Council of Agricultural Research (ICAR) has made an authentic and standardized classification of soils and divided the soils of India into the following 8 groups:
(1) Alluvial soils
(2) Black soils
(3) Red and Yellow soils
(4) Laterite soils
(5) Arid soils
(6) Saline soils
(7) Peaty and Organic soils
(8) Forest soils
Nature of Soil.
The alluvial soils are of many shades depending upon depth, (deep and shallow), deposition conditions (coarse and finer) and time (older and recent). In the western Ganga plains, Punjab and Haryana, the quantity of loam and clay loam increases while in the middle Ganga plain sand decreases and loam increases.
In Punjab and other plains, the excess of irrigation has made the soils waterlogged and saline crusts have been formed. This has also caused the formation of heavy soils in low lying areas.
In the eastern parts finer particles predominate and loams and fine silty clays are formed. Due to heavy rainfall, the alluvial soils have been laterised.
In the river valley plain of northern India floods result in deposition of silt. This new alluvium is known as Khadar. The higher areas, where floods do not reach has old alluvium and is known as Bangar.
Under the bangar deposits, beds of lime modules are found and are known as Kankar and these are usually found in Haryana and are a good source of raw material for cement plants.
Along the coast of the Peninsula, where sea water enters the delta, saltish soils are the result. The salt encrustations in Kutchch (Gujarat) shine with a glaze on sunny days.
In the north-west, the drier parts draw sodium, potassium, calcium, magnesium, etc. from the depth and create a powdery layer on the top of the soil because of evaporation of water.
This layer is called Reh (Kallar). No vegetation grows on the Kallar land.
Alluvial soils arc found in two different and distinct regions in India:
(i) Northern Plains.
The whole of the northern plains; from Punjab, Haryana, U.P., Bihar to West Bengal arc included in this region. The river courses and the deltas form alluvial soil regime.
(ii) Southern Coastal Area.
Starting from the Eastern Coast along a narrow belt passing through the flood plains, terraces, deltaic and lagoon areas of the rivers like the Mahanadi, Godavari, Krishna, Cauvery, etc.
Narrow areas along the coast and lower portions of the Narmada, the Tapti, the Sabarmati and the Mahi also have such type of soils.
The alluvial soils are fertile and are responsible for making the northern plains, the granary of India. Agricultural activities and crop productivity are attributed to these soils.
Black soils are said to have developed in the Deccan Trap area on basalt rocks in semi-arid conditions. They are of three kinds- shallow, medium and deep. These are also called Regur.
They are deep black in colour but there is almost complete absence of humus. Water can remain stored in the soils for a long period and this can continue to provide water to the roots of the plants in the dry period.
That is why these soils are used for the cultivation of cotton even in those areas where irrigation is not available. Their black colour is due to certain salts. On getting dry, the soils develop cracks. The soils have some deficiency of potash, nitrogen and phosphorus but have lime, magnesium, aluminium, etc. Thus they are fertile soils.
Such soils are in eastern Gujarat, south-western M.P (Narmada, parts of Vindhya and Satpura), almost the whole of Maharashtra, northern Karnataka, north-western T.N., western A.P, etc.
They are about 6 metres deep in the lower parts of the Narmada, the Tapti, the upper parts of Godavari and the Krishna rivers.
Black soils are very conducive to cotton cultivation. The Deccan Trap area has become famous for cotton cultivation because of these soils. In fact this region is called cotton bowl of India.
Wherever soils arc less deep as on the slopes of the plateaus and hills, and unable to hold water, there instead of cotton, barley, millets, pulses etc. are grown. In areas of deep soils, besides cotton, a host of other crops like tobacco, groundnuts etc. are successfully raised.
Red And Yellow Soils
The reddish-yellow colour is due to the presence of iron oxide. These soils are formed where the rainfall is low and there is a little leaching lesser than that in the laterite soils.
Red soils are as such usually developed on old crystalline and metamorphic rocks. These are sandier and comparatively less clayey.
These soils cannot retain moisture for a longtime. Use of manures increases their fertility. The soils are deficient in phosphorus, nitrogen and humus. They are acidic in nature and have iron, aluminium and lime in sufficient quantities.
If the soils are fine grained, they are fertile. These are porous soils. They are not fertile on higher dry lands.
These soils are found in three regions:
(i) Central- From Bundelkhand, Baghelkhand to the south, from Orissa, eastern A.P and T.N., these soils occupy large areas.
(ii) Western- The eastern and south-eastern narrow belt to the eastern side of the Aravalis.
(iii) Eastern- Parts of Meghalaya, Nagaland, Manipur, Mizoram, etc.
If the soils are not fertile, millets are grown. Where they are deep, deep red and fertile, the main crops grown are wheat, cotton, potato, rough grains and others.
These soils are in those areas which are hot and get seasonal rainfall. Due to higher temperatures the bacteria eat away humus and the rainfall leaches silica and lime. As a result the soils are acidic and are rich in aluminium and iron oxides.
At places where aluminium compounds dominate, the laterites are called bauxite. On account of presence of iron oxides in them the soils appear red.
These soils are classified into three types on the basis of their particles:
(a) Deep Red Laterite.
They have excess of iron oxide and potash but are short of Kaolin. The soils are not fertile.
(b) White Laterite.
The colour of the soil is due to excess of Kaolin. Soils lose fertility at a faster rate.
(c) Underground Laterite.
The upper parts are dissolved especially in iron which settles down below the upper layer. This makes the soils fertile.
Laterite soils do not retain moisture. The use of manure is necessary for increasing soil fertility.
Their occurrence is not spread on large areas but they occur in patches, however, continuous also in some areas. Bihar and Jharkhand Plateau has laterite soils. They are in patches on the Eastern Ghats through Orissa, A.P and T.N.
In the western parts of India such soils are in a narrow belt from the north to the south through Maharashtra, Karnataka and Kerala extending more or less continuously. Shillong Plateau has a laterite soil belt which extends towards Sadiya in Assam.
Soils are useful for making bricks because of presence of lot of iron in them. Its form in-which aluminium is in excess is called Bauxite and is used for extracting aluminium. Soils become fertile with the addition of fertilisers and manures.
These soils are devoted to the cultivation of cotton, rice, wheat, pulses, tea, coffee, etc. These are intensively cultivated in south India. Tapioca and cashew nuts are also grown in these soils. The latter is a cash crop.
These soils are usually shallow. They have sandy texture. They have low clay and salt content; usually below 10%. The colour ranges from red to brown and light brown.
Due to high evaporation in arid regions, the soils suffer from deficiency of humus and moisture but wherever water is provided through irrigation, soils become fertile. Though these soils are poor in nitrogen yet they are somewhat rich in plant food.
The entire area, west of the Aravalis has arid soils. This is the part of the Thar Desert and it continues into neighbouring Pakistan. The strong desert winds remove fine particles of sand to far off places causing infertile barren lands.
The use of manures and provision of irrigation facilities to such soils result in fairly good crop yields.
Afforestation can help stabilizing shifting sand dunes. Indira Gandhi canal has proven to be a boon for the region by way of converting dry desert lands into blooming landscape full of greenery and economic prosperity.
Saline soils are found in various climatic regimes – dry, semi-dry and swampy. These soils possess sodium, potassium and magnesium salts. Salts reach these areas by defective drainage and dry climate.
The salts in their solutions move up and are found lying over the surface like a white sheet. Its encrustation is very hard and inpenetrable. It does not allow any vegetation to grow.
The S.W Monsoons which cross Rann of Kutchch bring with them salt particles and form a layer in the Gujarat state. In the swampy areas and in the coastal tidal areas, the swamps are saturated with salts. These soils arc deficient in nitrogen and calcium.
The western Gujarat area (Kutchch) is known for these type of soils. These soils are known as Khar, Khanjan, etc. In the Cauvery and Mahanadi deltas, the sea water makes the soil saline.
In West Bengal the Sunderbans are well known for such soils. In Punjab, Haryana, U.P and Bihar, Saline soils are encompassing more and more agricultural areas. Same is the position in the southern Indian states.
However, the fertility of soils can be regained by way of putting gypsum in the soils and improving drainage.
Peaty and organic soils
A large amount of dead organic matter accumulates in areas which have heavy rainfall and high humidity.
As a result these soils are saline, rich in organic matter (40%) but deficient in potash and phosphorus. These are alkaline, heavy and black in colour.
Such soils are found in the coastal areas of W. Bengal, Orissa and Tamil Nadu, northern Bihar and Almora area of U.P.
These soils are found in the hilly areas, covered with forests. The main characteristic of these soils is the accumulation of organic matter derived from forest cover. The soils are not uniform everywhere but there are variations in their distribution.
The soils are loamy and have silt in the valley areas and are coarse grained, kankar etc. in the higher areas.
There are some important types of soils which have been spread over areas described below:
(i) Fine Textured Soil.
Usually the outwash and river valleys develop these type of soils. For example, in many areas of upper Himalayas (Lahul-Spiti, Kinnaur and even in Ladakh), soils have not fully developed as such stone, kankar and shallow soils are met with.
(ii) Alpine Soil.
In the higher areas about 3,000 metres high, the climate is cold. As a result, the soils have undecomposed vegetative matter derived from grasses resulting in immature soils.
The area where Podzol soils are found varies in height from 2,000 to 3,000 metres. The soil consists of partly decomposed vegetation derived from the coniferous forests that grow at this height.
Heavy rainfall results in leaching of the soils and turns it acidic. Its colour is greyish brown. Soils are not much fertile.
(iv) Lower Forest Soil.
The height of the mountainous area where these soils develop lies between 1000 to 2000 metres.
The forest cover is mostly of deciduous trees. The soils are brown in colour, deep and slightly acidic. The soils have humus and are thus fertile.