A History of Agriculture in India v1.c8.s2.t1: Indo-Gangetic Alluvium
A History of Agriculture in India v1.c8.s2.t1
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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.