1. COMPOSITION OF SOIL: Soil is the loose material which forms the upper layer of the mantel rock, i.e., the layer of loose fragments which covers most of the earth’s land area. It has definite and constant composition. It contains both decayed plants and animals substances. The four main constituents of soils are;

(i) Silica: The chief constituent of sand

(ii) Clay: is a mixture of silicates and contains several minerals such as iron, potassium, calcium, sodium and aluminum. Particles of clay absorb water and swell.

(iii) Chalk: (calcium carbonate) provides calcium, the most important element for the growth of plants.

(iv) Humus: is not a mineral, it is an organic matter. It is formed by decomposed plant remains, animal manure and dead animals and is the most important element in the fertility of the soil. It helps retain moisture in the soil and helps the plant in absorbing materials from the soil for building its body. A soil looks dark on account of the presence of humus.

2. TOP SOIL AND SUB SOIL: Two layers namely top soil and sub soil. Top soil(the upper layer) is of greater importance. Good top soil means good crops. It varies considerably in depth and also in character and ability to grow crops. It is only a few meters deep. Million of bacteria, insects and worms live in it. Top soils develop very slowly. It may take years to form top soil suitable for plants, but it can be washed away in a few years if proper precautions are not taken. Sub soils consist of the parent material from which soil is formed. It also contains plant food and moisture but it is not a s productive as top soil. It has to be converted into soil and it may take years to convert sub soil into soil. Below the sub soil generally there is solid rock.

3. FORMATION OF SOIL: The natural processes involved in the formation of soil are

(i) Weathering: process of disintegration of rocks into soil.

(ii) Deposition: process of progressive lying down of rock particles carried by rivers, ice, marine, currents wind or tides.

(iii) Biochemical processes

Soil formation depends upon the following factors;

*Nature of the parent rock, * Climate, * Natural Vegetation, * Topography, * Time


a) Sandy Soil (light soil): It contains more than 60% sand and les than 10% clay. It is easy to cultivate and is favoured for fruits and vegetables.

b) Clayey Soil: It has high proportion of clay. It becomes sticky when mixed with water. A soil very rich in clay is called ‘heavy’,

c) Loam: is rich soil and consist of a mixture of sand and clay. All loamy soils are good for farming and general gardening.


The Indian Council of Agricultural Research (ICAR) classifies the soils of India into eight categories.

6. ALLUVIAL SOIL: This is the most important and widespread group of soils. It covers about 15 lakh of the land area in Great Plains from Punjab to Assam and also in the valleys of the Narmada and Tapi, Mahanadi, Godavari, Krishna and Cauvery. These soils have been brought down and deposited by three great Himalayan rivers Sutlej, Ganga and Brahmaputra. These soils consist of varying proportions of san, silt and clay. Khadar is the newer alluvium which is sandy, light coloured and occurs near river beds where deposition takes place regularly and bhangar or older alluvium. Alluvial soils as a whole are very fertile and therefore the best agricultural soils of the country. The regions of these of these soils constitute the’ wheat and rice bowls’ of India.

7. BLACK SOIL: As the name indicates these soils are black in Colour and since they are ideal for growing cotton, they are also called cotton soil. These soils, covering an area of 5.46 lakh, are most typical of the Deccan trap (Basalt). The black Colour of regur is variously attributed to the presence of titaniferrous magnetite, compounds of iron and aluminum-Unsuitable for heavy irrigation. Ideally suited to dry farming. Suitable for cotton, cereals, oilseeds like linseed, castor and safflower, many kinds of vegetables and citrus fruits.

8. RED SOIL: These soil occupy about 5-18 lakh over the peninsula reaching up to Rajmahal Hills in the east, Jhansi in the north and Kutch in the West. In North western peninsula is covered by the black soils and the remaining south-eastern half is covered by red soils- Entire black soil in the eastern part of Peninsula comprising of Chhotanagpur plateau, Orissa, east Madhya Pradesh, Telengana, the Niligris, Tamilnadu plateau and Karnataka. The soil have reddish colour due to iron compounds. It is suitable for rice, ragi, tobacco and vegetables.

9. LATERITE SOILS: These soils occupying an area of 1.26 lakh Found capping the flat uplands, and are spread in western coastal region receiving very heavy rainfall – Poor in nitrogen, phosphoric acid, potash, lime – suitable for rice, ragi, tapioca and cashewnuts.

10. FOREST AND MOUNTAIN SOIL: These soils occupy about 2.85 lakh in the hilly regions of the country – described as soils in the making – found in the Himalayas and the other ranges in the north and high hill summits in the Sahyadris, Eastern Ghats and Peninsula – poor in potash, phosphorous – Temperate fruits, maize, wheat and barley are grown in Jammu and Kashmir and Himachal Pradesh where soils are mostly podzols which are acidic in re-action.

11. ARID AND DESERT SOILS: Northwestern parts of the country and occupy about 1.42 sq. km area in Rajasthan, south Haryana, north Punjab and Rann of Kutch. Thar Desert alone occupies an area of 1.06 sq. km. It contains high percentage of soluble salts and a low to very low organic matter.

12. SALINE AND ALKALINE SOILS: These soils occupy about 170 lakh sq. km of arid and semi-arid areas of Rajasthan, Punjab, Haryana, Uttar Pradesh, Bihar and whole of Maharastra. Textually they are sandy to loamy sand. Saline soils contain free sodium. Crops grown on these soils include rice, wheat, cotton, sugarcane and tobacco.

13. PEATY AND MARSHY SOILS: These soils cover an area of about 150 sq. km in the Kottayam and Allepey districts of Kerala. They are suitable for paddy cultivation.

14. SOIL FERTILITY: The factor responsible for deficiency of Indian soils are: (i) loss of nutrients, largely brought about through the removal of harvested crops, (ii) leaching which occurs under heavy monsoonal rains, causes loss of nutrients, sandy soils are more subject to leaching than the heavier ones and bare soils are more than those covered by plants. Indian soils are mainly deficient in nitrogen, phosphorus and potash. These can be supplied to the soils by application of organic manures and fertilizers.

15. SOIL EROSION: Soil erosion is the removal of soil particles by natural agencies such as water and wind and also as a result of human and animal interference.

16. TYPES OF SOIL EROSION: Two types of soil erosion:

(i) Water Erosion: The important types of this erosion are sheet, rill and gully. In sheet erosion thin layer of soil is removed by the water during heavy rains. If the erosion continues unchecked, numerous finger-shaped grooves may develop all over the area as a result of the silt-landen run-off. This is called rill erosion. The rills may deepen and enlarge into gullies.

(ii) Wind Erosion: Wind erosion is mainly confined to arid and semi-arid areas devoid of vegetation. Wind, particularly during sand-storms, lifts and carries away soil particles leaving behind a depression devoid of top fertile soil. Rajasthan and the adjoining areas of Haryana, Uttar Pradesh and Gujarat show this type of soil erosion.

17. CONSEQUENCES OF SOIL EROSION: (i) heavy floods in rivers, (ii) lowering down of sub soil water level, (iii) reduction of soil fertility, (iv) silting of streams and water courses, (v) disappearance and downfall of civilizations.

18 a) SOIL CONVERSATION: Soil conservation is an effort made by man to prevent soil erosion to retain the fertility of soil. It may not be possible to stop soil erosion entirely.

b) Measures for Soil Conservation: 
(i) Planting cover crops, 
(ii) Adoption of correct farming techniques, 
(iii) Terracing the practice of cutting steps in hillside, to create level land for cultivation, 
(iv) Construction of check dams, 
(v) Creation of wind break, 
(vi) Controlling of grazing of pastures, 
(vii) Suspending cultivation for one season and more so as to help the soil recover its fertility