What is Soil?
· Soil is the thin top layer on the earth’s crust comprising rock particles mixed with organic matter.
· Soil is made up in part of finely ground rock particles, grouped according to size as sand and silt in addition to clay, organic material such as decomposed plant matter.
What is the difference between Pedology and Pedogenesis?
· Pedology is the study of soils in their natural environment while Pedogenesis is the natural process of soil formation that includes a variety of processes such as weathering, leaching, calcification etc.
How many different types of soil are there?
· There are three main types of soil—clay, sandy, and loamy.
· There are also other types of soil, depending on the type of underlying rock and the climate and vegetation.
· Loams are a mixture of clay, sand, and silt, and are more fertile than other soils.
· Clay soils are usually sticky and waterlogged.
· Sandy soils are basically of sandy texture. This type of soil has poor clay content and also lacks in moisture content.
Classification of Indian Soils
» Soil is a valuable resource of India. Much of the Indian agriculture depends upon the extent and qualities of soil.
» In the ancient period, the classification was based on only two things; whether the soil is fertile or sterile. Thus the classification were:
1) Urvara [fertile]
2) Usara [sterile]
» In the modern period, when men started to know about the various characteristics of soil they began to classify soil on the basis of texture, colour, moisture etc.
» The rocks from which soils are formed are called parent materials.
» In most of the cases, the parent material determines the colouration, mineral composition and texture of the soil.
» When the Soil survey of India was established in 1956, they studied soils of India and their characteristics.
Major Types of Soils in India
1. Alluvial soil [43%]
2.Red soil [18.5%]
3.Black / Regur soil [15%]
4.Laterite soil [8.67%]
5.Arid / Desert soil
6.Mountain Soil [8%]
Major types and Characteristics of Soils in India
· Alluvium is loose, unconsolidated (not cemented together into a solid rock) soil or sediments, which has been eroded, reshaped by water in some form, and redeposited in a non-marine setting.
· Alluvium is typically made up of a variety of materials, including fine particles of silt and clay and larger particles of sand and gravel.
· When this loose alluvial material is deposited or cemented into a lithological unit, or lithified, it is called an alluvial deposit.
· These soils are formed by the deposition of sediments by rivers.
· They are rich in humus and very fertile.
· Alluvial soil in India is rich in Potash. However it is deficient in Phosphorous.
· They are found in Great Northern plain, lower valleys of Narmada and Tapti and Northern Gujarat.
· These soils are renewed every year.
· Wheat, rice, maize, sugarcane, pulses, oilseed etc are cultivated mainly.
· Red soil is a group of soil that develops in a warm, temperate, moist climate under deciduous or mixed forests and that have thin organic and organic-mineral layers overlying a yellowish-brown leached layer resting on an illuvial red layer.
· Red soils generally derived from crystalline rock.
· They are usually poor growing soils, low in nutrients and humus and difficult to cultivate because of its low water holding capacity.
· Red soils denote the second largest soil group of India covering an area of about 6.1 lakhs sq. km (18.6% of India's area) over the Peninsula from Tamil Nadu in the south to Bundelkhand in the north and Rajmahal hills in the east to Kachchh in the west.
· They surround the black soils on their south, east and north.
· These soils are found in large tracts of western Tamil Nadu, Karnataka, southern Maharashtra, Chhattisgarh, Telangana, Andhra Pradesh, Odisha and Chotanagpur plateau of Jharkhand. Scattered patches are also seen in Birbhum (West Bengal), Mirzapur, Jhansi, Banda, Hamirpur (Uttar Pradesh), Udaipur, Chittaurgarh, Dungarpur, Banswara and Bhilwara districts (Rajasthan).
· Black soil is formed by the decomposition of lava rocks. Hence this type of soil is mostly found in the volcanic regions.
· It is usually found away from the coastal areas and is most suitable for growing cotton.
· Black soil in India is rich in metals such as Iron, Magnesium and Aluminum. However it is deficient in Nitrogen, Potassium, Phosphorous and Humus.
· Black soil is of red colour mainly due to its iron oxide content.
· This soil shares 15 % of all types of soil in India.
· These soils are made up of volcanic rocks and lava-flow.
· It is concentrated over Deccan Lava Tract which includes parts of Maharashtra, Chhattisgarh, Madhya Pradesh, Gujarat, Andhra Pradesh and Tamil Nadu.
· Regur means cotton – best soil for cotton cultivation
· Laterite soils are mostly the end products of weathering.
· They are formed under conditions of high temperature and heavy rainfall with alternate wet and dry periods.
· Heavy rainfall promotes leaching (nutrients gets washed away by water) of soil whereby lime and silica are leached away and a soil rich in oxides of Iron and Aluminium compounds is left behind.
· Hence laterite soil in India is rich in Iron and Aluminium. However it is deficient in Nitrogen, Potash, Potassium, Lime, Humus.
· They are commonly found in Kerala, Tamil Nadu, Maharashtra, Chhattisgarh and hilly areas of Orissa and Assam.
· These soils are generally infertile. Some plants like tea, coffee, coconut, areca nut, etc. are grown in this soil.
· Rice, Ragi, Sugarcane and Cashew nuts are cultivated mainly in this soil.
Arid / Desert Soils
· Most desert soils are called Aridisols (drysoil).
· Desert soils are basically of sandy texture. This type of soil has poor clay content and also lacks in moisture content.
· In the desert regions of Rajasthan, soils are not well developed.
· As evaporation is in excess of rainfall, the soil has a high salt content and saline layer forms a hard crust. These soils are deficient in organic matter i.e. Nitrogen is insufficient and Phosphate is normal
· These soils are commonly found in Rajasthan, Haryana and the South Punjab.
· Wheat, Bajra, Groundnut, etc. can be grown in this soil.
· Mountain soils are mainly found on the hill slopes.
· These soils are formed due to mechanical withering caused by snow, rain, temperature variation etc.
· These mountain soils are found in hilly regions of Jammu and Kashmir, Sikkim, Assam and Arunachal Pradesh.
· These soils occupy about 8% of the total land area of India.
· The soils are very rich in humus but are deficient in potash, phosphorus and lime.
· The soils are especially suitable for plantation of tea, coffee, spices and tropical fruits.
· They are found in Himalayan region and vary in different regions according to altitude.