It is a mixture of rock debris and organic material, soils are living systems.
The three layers of soil found on Earth are called Horizons. The lowermost rock is known as the Parent rock or Bedrock.
- Horizon ‘A’ – topmost, where organic materials have got incorporated with minerals, nutrients and water.
- Horizon ‘B’ – transition zone between horizon A & C.
- Horizon ‘C’ – loose parent material. It is in 1st stage of soil formation and eventually forms A,B.
Arrangement of layers is known as Soil Profile.
Ancient times, the fertile soil was known as ‘Urvara’ and sterile soil was known as ‘Usara’.
Soil survey of India, 1956 conducted studies in the Damodar valley under the National Bureau of Soil Survey, Land use planning under ICAR- Indian Council of Agricultural Research.
Classification of types of Soil in India:
On the basis of USDA soil taxonomy, the types of Soil in India are:
- Inceptisols – covers 39% area in India
- Entisols – covers 28% area in India
- Alfisols – 13 % area in the country
- Vertisols – 8% area in India
- Aridisols 0 4% area of the soils in India
- Ultisols – 2% area in India
- Mollisols – 0.4% area in India
On basis of genesis, colour, composition and location, soil types in India are:
- Alluvial Soil
- Red and yellow Soil
- Laterite Soil
- Saline Soil
- Forest Soil
- Black Soil
- Arid Soil
- Peaty Soil
It is depositional soil found in northern plains and river valleys. It is rich in potash, poor in Phosphorus. The colour of alluvial type of soil in India is light to dark grey.
Two types of alluvial is found in the Ganga plains – Khadar(new, deposited annually, enriches the soil by deposition of fine silts) and Bhangar(older, deposited away from flood plains, contains calcareous kankars).
Deccan, parts of Maharashtra, MP, Gujarat, Andhra pradesh and some parts of Tamil Nadu.
Upper reaches of Godavari & Krishna has deep deposits. Also called “Regur soils” or “Black cotton soil”. It slowly absorbs moisture and slowly loses it. Therefore, it retains moisture for long time, this is aboon for rainfed crops.
‘Self Ploughing’ – develops cracks when dry, swells up when it absorbs moisture.
Rich in lime, iron, magnesia, alumina. Lacks phosphorus, nitrogen, organic matter. The colour of Black soil is deep black to grey.
Red and Yellow Soil:
It develops on crystalline igneous rocks in areas of low rainfall. Especially in Eastern and Southern Deccan. Red colour due to wide diffusion of iron in crystalline and metamorphic rocks. Yellow colour when it is in hydrated from. These soils are fine grained and fertile. It is poor in nitrogen, phosphorus and humus.
It develop in areas with high temperature and high rainfall. It is result of intense leaching during high rainfall. Lime and silica leached away. It is rich in iron oxide and aluminium compound. Humus removed by swift bacterial action in high temperature. It lacks nitrogen, phosphate, calcium. Laterite soil is not suitable for cultivation in TN, AP, Kerala, cashew nut and Tapioca is grown using fertilizer and manures. It is used in bricks for construction.
Arid type of Soil in India:
Sandy structure, saline nature, dry climate. Lack moisture and humus.
It lacks nitrogen, while phosphate is present in normal amount. At the lower horizons of soil ‘kankars’ occur because the calcium content increases downwards.
It is known as ‘Usara Soil’. It has sodium, potassium, magnesium which makes it infertile. Saline soil lacks nitrogen and calcium. It occurs in arid and semi-arid regions.
In Rann of Kachchh, southwest monsoon brings salt and deposits as a crust. Seawater intrusions in deltas promote saline soils. Excessive irrigation in dry conditions promote capillary action resulting in deposition of salt on top. Addition of gypsum to solve salinity of soil.
It found in areas of heavy rainfall and high humanity. It has large quantity of organic matter which is rich in humus upto 40-50 percent. It is sometimes alkaline.
Peaty soil is heavy and black in colour. This type of soil is found in Northern Bihar, Southern Uttaranchal, coastal West Bengal, Orissa, Tamil Nadu.
It is located in forest area with sufficient rainfall. It is found in snow-bound areas of Himalayas, acidic with low humus content. Located in lower valleys, it is fertile.
Destruction of the soil cover is known as soil erosion. generally, rate of removal of fine particles, i.e., Soil erosion, is equal to rate of soil formation. But if the soil balance is disturbed by natural and human factors; wind and water are powerful agents of soil erosion.
Sheet erosion: On flat lands, due to heavy rainfall removes finer and more fertile top soil.
Gully erosion: On steep slopes. A region with a large number of deep gullies/ ravines is called a badland topography in Chambal basin, Tamil Nadu and West Bengal.
Eroded materials is carried by rivers increasing their value and can cause floods by reducing the carrying capacity of rivers.
Causes of soil erosion:
- Shifting cultivation
- Over-irrigation makes soil saline
- Chemical fertilizers harden and reduce soil fertility if enough humus not given.
It is a methodology to maintain soil fertility, prevent soil erosion and exhaustion and improve degraded condition of the soil.
Method of Soil conservation – Contour bunding, contour terracing, regulated forestry, agro-forestry in arid areas, controlled grazing, cover cropping, mixed farming, crop rotation, construction of check dams to prevent gullies. Lands with 15-25 % gradient should not be cultivated without terracing. Finger gullies are eliminated by terracing. The extension of gullies is checked by Gully plugging.
Central Arid Zone Research Institute (CAZRI) is involved in integrated land use planning for soil conservation.