A History of Agriculture in India v1.c8.s2: Soil Types
A History of Agriculture in India v1.c8.s2
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Contents
- v1.c8.s2.t1 Indo-Gangetic Alluvium — 12 parts
- v1.c8.s2.t2 Black Cotton Soils — 6 parts
- v1.c8.s2.t3 Red Soils — 7 parts
- v1.c8.s2.t4 Laterites — 14 parts
- v1.c8.s2.t5 Other Soil Groups — 8 parts
Soil Types
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The investigations of Voelcker in 1893, and those of Leather in 1898, led to a classification of Indian soils into four major types: (i) the Indo-Gangetic alluvium; (ii) the black cotton or *regur* soils; (iii) the red soils lying on metamorphic rocks; and (iv) the lateritic soils. Various types of soils, according to the findings of the Soil Survey of India, are shown in Fig. 4.
Indo-Gangetic Alluvium
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The Indo-Gangetic alluvium is by far the largest and most important of the soil groups of India. The soils of this group cover about 777,000 square kilometres. They are distributed mainly in the northern, north-western and north-eastern parts, including the Punjab, Haryana, Uttar Pradesh, Bihar, Bengal, and parts of Assam and Orissa. They produce bumper crops of wheat and rice (Fig. 5).
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In spite of numerous subordinate variations, the main features of these soils result from their having been deposited as silts by the numerous tributaries of the Indus, the Ganges and the Brahmaputra river systems, which drain the Himalayas, bringing with them the products formed by the weathering of rocks.
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Geologically the alluvium is divided into (i) *khadar*, or new alluvium of
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INDIA SOIL MAP
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| 1. Alluvial | 11. Medium black | 21. Brown soil |
| 2. Alluvial (highly calcareous) | 12. Shallow black | 22. Forest soil |
| 3. Alluvial on coastal alluvium | 13. Black soil saline and alkaline | 23. Podsolic soil |
| 4. Alluvial on deltaic alluvium | 14. Black soil undifferentiated | 24. Foothill soil |
| 5. Alluvial and alkaline | 15. Red and black | 25. Mountain and hill soil |
| 6. Pedocal sierozem | 16. Ferruginous | 26. Mountain meadow soil |
| 7. Pedocal brown soil | 17. Ferruginous gravelly | 27. Peat |
| 8. Grey and Brown | 18. Red and Yellow | 28. Glaciers |
| 9. Desert soil | 19. Laterite | 29. Soil boundary |
| 10. Deep black soil | 20. Laterite and lateritic | 30. State boundary |
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sandy composition, generally light in colour, about 10,000 years old, and (ii) *bhangar*, or the older alluvium of Pleistocene date, of more clayey composition, generally of dark colour, and full of pebbles or *kankar*. The soils differ in consistency from drift sand to loams, and from fine silts to stiff clays. A few pebble beds are also occasionally met with. The presence of impervious clays obstructs the drainage, and also promotes the accumulation of injurious salts of sodium and magnesium, which make the soils sterile.
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The formation of hard pans at certain levels in the soil profile as a result of the binding of soil grains by the infiltrating silica or calcareous matter is often observed in these alluvial soils. Layers of *kankar* in the Indo-Gangetic alluvium of Uttar Pradesh and West Bengal, and those composed of impure iron oxides are instances of these hard pans.
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The soils of the Punjab and Haryana plains belong to the alluvial class typical of the Indo-Gangetic plains. A majority of the soils are loams or sandy loams, with a soil crust of varying depth. Hardly any profile characteristics are observed. Soluble salts are present in considerable quantities. The lower layers contain *kankar* nodules. The soil character is generally alkaline due to the presence of sodium in the clay complex. The soils are rich in phosphorus and potash, but are deficient in organic matter and nitrogen.
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Two broad divisions are distinguished in Bihar: (i) the alluvium found north of the Ganges, and (ii) the alluvium found south of the Ganges. The soils in the first group are clayey, loam to sandy loam, neutral to alkaline, rich in potash, and deficient in P₂O₅, while those in the second group are heavier and finer in texture, with higher K₂O and P₂O₅ contents, and of acidic pH in the southernmost parts.
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In West Bengal, the Rarh tract consists mainly of old alluvium. There is hardly any regularity in the manner of deposition of river-borne materials. Some of the early deposits display considerable diversity on account of their long subjection to climatic and other influences.
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The alluvial soils of Tamil Nadu are transported soils, found mainly in the deltaic areas and on the coastal line. A section of the profile shows alternate layers of sand and silt. The composition of the strata varies with the nature of the silt brought by the rivers which, in turn, varies with the catchment areas and the tracts through which the streams flow.
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The light sandy red and yellow soils found in the Mahanadi basin are of alluvial origin. The formations in the north and on the west coast of Kerala consist mostly of the sands deposited from the sea. They are of low fertility.
Black Cotton Soils
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The typical soil of the Deccan Trap is the *regur* or black cotton soil. It is common in Maharashtra, in the western parts of Madhya Pradesh, Karnataka, and some parts of Tamil Nadu, including the districts of Ramnad and Tinnevelly in the extreme south. It is comparable with the chernozems of Russia and with the prairie soil of the cotton-growing tracts of the United States of America, especially the black adobe of California. It is derived from two types of rocks: the Deccan and Rajmahal Trap, and the ferruginous gneisses and schists occurring in Tamil Nadu under semi-arid conditions. The former attains sometimes considerable depths, whereas the latter are generally shallow.
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The black soil areas have, generally, a high degree of fertility, though some, mainly in the uplands, are of low productivity. The soils on the slopes and the uplands are somewhat sandy, but those in the broken country between the hills and the plains are darker, deeper and richer, and are constantly enriched by deposits washed down from the hills.
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Black soils are highly argillaceous, fine-grained, and dark with a high proportion of calcium and magnesium carbonates. They are very tenacious of moisture, and are exceedingly sticky when wet. Owing to considerable contraction on drying, large and deep cracks are formed. They contain much iron and fairly high quantities of lime, magnesia, alumina, and potash. However, they are poor in phosphorus, nitrogen and organic matter. In all regur soils, in general, and in those derived from ferromanganesian schists, in particular, there is a layer rich in kankar nodules formed by the segregation of calcium carbonate at some depth below the surface and above the weathered rocks. The soils are generally rich in montmorillonitic and beidellitic groups of minerals.
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In Maharashtra, the soils derived from the Deccan Trap occupy quite a large area (Fig. 6). On the uplands and on the slopes, the soils are light-coloured, thin and poor. On the lowlands and in the valleys, relatively clayey black soils are found. Along the Ghats, the soils are very coarse and gravelly. The soil is often some 6 metres deep in the valleys of the Tapti, the Narmada, the Godavari and the Krishna rivers. The subsoil contains a good deal of lime. Outside the Deccan Trap area, the black cotton soil predominates in the Surat and Broach districts of Gujarat.
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In Madhya Pradesh, two distinct kinds of black soils are found: (i) deep heavy black soil covering the Narmada valley, and (ii) shallow black soil. The cotton-growing areas generally have deep and heavy black soils, though soils of lighter texture are also found.
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The black soils of Karnataka are fairly heavy, with a high salt concentration. They are generally rich in lime and magnesia.
Red Soils
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Red soils extend practically over the whole Archaean basement of Peninsular India, from Bundelkhand to the extreme south, covering 2,072,000 square kilometres, embracing south Bengal, Orissa, parts of Madhya Pradesh, eastern Andhra Pradesh, Karnataka, and a major part of Tamil Nadu. These soils also occur in Santhal Parganas in Bihar, and in the Mirzapur, Jhansi and Hamirpur districts of Uttar Pradesh. They were produced as a result of meteoric weathering of ancient crystalline and metamorphic rocks. These soils started developing around the Mesozoic and Tertiary ages.
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The colour of these soils is generally red, grading sometimes into brown, chocolate, yellow, grey and even black. The redness is due more to a general diffusion than to a high proportion of iron content.
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The soils grade from the poor, thin, gravelly and light-coloured varieties of the uplands to the much more fertile, deep, dark varieties of the plains and the valleys. They are generally poor in nitrogen, phosphorus and humus. Compared with regur, they are poor in lime, potash and iron oxide, and are also uniformly low in phosphorus. The clay fraction of the soils is rich in kaolinite.
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Red soils can be divided into two broad subgroups: (i) red loams of argillaceous character with a cloddy structure and possessing a few concretions, and (ii) red earths with loose and friable top soil, rich in secondary concretions and sesquioxide type of clay.
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More than two-thirds of the cultivated area in Tamil Nadu is covered by red soils. They are in-situ formations, produced from the rock below under the influence of climatic conditions. The rocks are acidic, consisting of mica or red granites. The soils are shallow and open in texture. They have a low exchange capacity and are deficient in organic matter and plant nutrients.
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The predominant type in the eastern tract of Karnataka is the red soil overlying granite. It is rich in potash, iron and alumina.
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The acidic soils in the south of Bihar are red soils. In West Bengal, the red soils, sometimes misrepresented as laterites, are the transported soils from the hills of the Chhota Nagpur plateau. A part of the Jhansi District in Uttar Pradesh also has red soils. A broad strip of area running between eastern and western parts of Coorg is red loam, easily drained, and having fairly dense vegetation.
Laterites
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Laterite is a soil type peculiar to India and some other tropical countries, characterized by the intermittent occurrence of moist climate. In formation it varies from compact to vesicular rock composed essentially of a mixture of hydrated oxides of aluminium and iron, with small quantities of manganese oxides, titania, etc. It is produced by the atmospheric weathering of several types of rocks.
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Laterites may break and be carried to lower levels by streams. When redeposited, they become a compact mass by the segregative action of the hydrates. Thus there are high-level laterites resting on the rocks, and low-level laterites formed in the usual way of detrital deposits.
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Fig. 5. The Indo-Gangetic plain in the Punjab has a rich alluvial soil, which produces bumper crops of wheat and rice
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Fig. 6. The deep black soils in the Pune District, Maharashtra, produce bumper crops of cotton, sugarcane and rice. The fields are dotted with trees of mango and *Acacia nilotica*. In the background are the flat-topped mountains of the Deccan Trap
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Fig. 7. The medium black cotton soil of trap and gneissic origin in the Coimbatore District, Tamil Nadu, yields rich crops of cotton and sugarcane
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Fig. 8. Barren Archaean granite is covered with a thin layer of soil at Hampi, in the Bellary District, Karnataka, Good soil is found only in the low-lying areas
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Laterites are specially well developed on the summits of the hills of Karnataka, Kerala, Madhya Pradesh, the coastal region of Orissa, south Maharashtra, Malabar and part of Assam. All lateritic soils are generally very poor in lime and magnesia, and deficient in nitrogen. Occasionally, the P₂O₅ content may be high, but there is deficiency of K₂O.
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In Tamil Nadu, there are both high-level and low-level laterites which are formed from a variety of rock materials under certain climatic and weather conditions. They are both in-situ and sedimentary formations, and are found along the coastal region where rainfall is heavy and the climate humid. The laterites at lower elevations grow rice, whereas those at higher elevations grow tea, cinchona, rubber and coffee. The soils are rich in nutrients and contain 10 to 20 per cent organic matter.
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In Coorg, the laterite appears sporadically almost all over the district. In Maharashtra it is found only in Ratnagiri. In the soils of Ratnagiri, coarse material is found in large quantities.
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In Kerala, in between the broad sea belt consisting of sandy soil and sandy loams and the eastern regions comprising forest and plantation soils, the mainland contains residual laterite. It is poor in total and available P₂O₅, available K₂O and CaO.
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The laterite soils of Karnataka are comparable with the laterites found in Malabar, the Nilgiris, etc. The soils have very low lime content on account of severe leaching and erosion.
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In West Bengal, the area between the Damodar and the Bhagirathi is interspersed with some basaltic and granitic hills with a laterite capping.
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In Bihar, the laterite occurs principally as a cap on the higher plateau, but is also found in fair thickness in some valleys.
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The laterites of Orissa are largely found capping hills and plateaus, occasionally in considerable thickness. Two types of laterites have been distinguished: (i) the laterite murrum, and (ii) the laterite rock. These are also found occurring together.
Other Soil Groups
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In addition to the four principal groups of soils described above, mention may be made of four more groups.
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*Forest and Hill Soils*: The soil formation is governed mainly by the character of the deposition of organic matter derived from the forest growth. Broadly, two conditions of soil formation may be distinguished: (i) soils formed under acid condition, with acid humus and low base status, and (ii) soils formed under slightly acid or neutral condition, with high base status, which is favourable to the formation of brown earths.
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The soils of the hill district of Assam have a high content of organic matter and nitrogen. This may be due to the virgin nature of these soils.
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In Uttar Pradesh, the sub-Himalayan tract comprises three distinct parts, viz. *bhabar* area immediately below the hills, *tarai* and the plains. The *tarai* areas are characterized by extreme unhealthiness owing to excessive soil moisture and prolific growth of vegetation.
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The weathering of metamorphic rocks in Coorg has produced deep-surface soil of great fertility, as it receives annually the decomposed products of the virgin forest. The areas towards the west are for the greater part reserved forests and mountain areas. The land surface is full of pebbles, is easily drained, and has a laterite bed.
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*Desert Soils:* A large part of the arid region of Rajasthan and the Punjab and Haryana, lying between the Satluj and the Aravallis, is affected by desert conditions which, geologically, are of recent origin. This part is covered under a mantle of blown sand, and is dominated by conditions which inhibit soil growth. Some of the soils contain a high percentage of soluble salts and varying percentages of calcium carbonate, and possess high pH. They are, however, poor in organic matter. Reclamation is possible only if proper irrigation facilities are made available.
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*Saline and Alkaline Soils:* These soils are extensively distributed throughout India in all the climatic zones. Many parts of the dry tracts of the north, especially in Bihar, Uttar Pradesh, the Punjab, Haryana and Rajasthan, give rise to saline and alkaline efflorescences in the same way as the soils capping the Upper Tertiary rocks do. There are many yet undecomposed mineral fragments in these alluvial clays and silts, which on weathering liberate salts of sodium, magnesium and calcium. The injurious salts are confined to the top layers, being deposited there by the capillary transference of saline solutions from the lower strata.
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It has been estimated that nearly 850,000 hectares in Uttar Pradesh and over 200,000 hectares in the Punjab and Haryana have been affected by *usar*. Over 10,000 hectares are being affected every year in the Punjab and Haryana. Alkali soils are met with all over Maharashtra.