A History of Agriculture in India v1.c8: Chapter 2

A History of Agriculture in India v1.c8

Language: English

Chapter 2 v1.c8.1

SOIL from the agricultural point of view may be defined as the material comprising weathered rock minerals which, together with organic matter, water and air, provides a medium for the growth of plants. This medium is the basic source of all human and animal food as well as of many industrial raw materials.

v1.c8.2

The agriculture of a country is dependent to a large extent on the nature of its soils, which, in turn, is influenced materially by climatic factors. Thus the soils of India, which extend from the temperate regions through the subtropical into the torrid regions, display marked differences in character, again reflected in the vegetation pattern of the country.

v1.c8.3

Although soils undergo important secondary modifications through climate, topography, organic agencies, etc., their fundamental character is determined by their general nature. Certain well-marked rock types give rise to certain definite types of soils; and variations in the rocks cause wide differences in the overlying soils in regard to their consistency, depth and composition.

v1.c8.4

The foundations of the soils of India have been classified into :

v1.c8.5

1. *Ancient crystalline and metamorphic rocks* : The oldest rocks constituting the basement of Peninsular India which occur as granites, gneisses, crystalline schists and subordinate rocks rich in ferromanganesian minerals. These rocks have given rise to red soils.

v1.c8.6

2. *Cuddapahs and Vindhyans* : Being an ancient formation, the soils derived are all highly matured.

v1.c8.7

3. *Gondwana* : It occurs in the chains of basin-like depressions in the table land of the peninsula filled with old river deposits, sands and silts. The Gondwana rocks have produced comparatively immature soils of less variety and fertility.

v1.c8.8

4. *The Deccan Trap* : It comprises volcanic lava rich in ferromanganesian and alumina compounds. The typical soil derived from the Trap is the *regur* type or the black cotton soil.

v1.c8.9

5. *Tertiary and Mesozoic sedimentary rocks of Extra-Peninsular India*, occupying small areas of the hilly and mountainous ground in depressions and valley basins : (i) Mesozoic and Eocene calcareous rocks; and (ii) Tertiary sandy rocks.

v1.c8.10

6. *Recent and sub-recent rocks*, which have given rise to a drift soil, entirely different in origin from the soils of southern India, which are largely residual soils produced from the decomposition products of rocks : Old Indo-Gangetic alluvium, new Indo-Gangetic alluvium; deltaic alluvium, lateritic rocks, and desert deposits.

v1.c8.11

Meteorological conditions in India, with their wide diversity, have given rise to major secondary modifications in the basic character of soils. The climates are manifold. The conditions in the north are very different from those in the south; the coasts present a marked contrast to the interior; the climate of the West Coast region is different from that of the East Coast tract, and the Himalayan zone is a class by itself. The normal annual rainfall varies from about 11,685 millimetres (460 inches) in the Assam hills to less than 76 millimetres (3 inches) in Rajasthan. During some months of the year, vast areas are deluged; during others, drought prevails. Under the influence of such climatic variations, geological differences have ceased to be of predominant importance, and soils of similar properties cover the most varied rock systems. The more extreme the climate, the more generally will the climatic type of soils predominate. Examples are the black soils derived from different types of rocks.

Formation of Soils

v1.c8.s1.1

A mature soil is the handiwork of geoclimatic and geobiological forces operating jointly. How do these forces operate? Soils are formed by the weathering and disintegration of rocks. Soils are either sedentary, i.e. those formed out of the underlying rock, or are transported, i.e. those formed out of the disintegrated parts of rocks, brought down by the action of rivers from a distance. The process of breaking down of rock masses and their gradual development into soil is called weathering. The agencies of weathering are physical, i.e. those that break the rock into smaller pieces, and chemical, i.e. those that change the composition of the minerals forming the rock and, in so doing, exert a marked influence upon its physical character. The work of the physical agencies is called decomposition. Both these processes are complementary to each other.

v1.c8.s1.2

The agencies operating in the disintegration of soils are: aqueous, atmospheric, physical and organic.

v1.c8.s1.3

The aqueous agency operating in the disintegration of rocks and soils is the most potent of all. What enormous quantities of solid matter are dislocated by rain and brought down by streams and rivers may be judged from Everest's calculation of silt carried down by the Ganges alone. Everest has calculated that 355,361,461 tonnes of solid matter are carried down annually to the sea by the Ganges. The erosive action of running water is due to sand, pebbles and rocks carried by it. The hardest and heaviest rocks become converted into rounded boulders and pebbles by the action of the moving water containing sand in motion. Water acts not only mechanically in denuding rocks, but it is also a solvent. Potash, soda, silica and lime get dissolved in water, and the rocks are denuded by the solvent action Fig. 3. The occurrence of Archaean and Purana Rocks and the Deccan Trap in India of water. The solvent action of water and minerals is increased by salts in solution and gases in suspension. Sea waves beating against cliffs also help in the formation of soils. The action of glaciers in tearing down rocks and in the formation of moraines and erratic boulders may be also included under this head. The hydration of rocks in the presence of water may also be mentioned.

v1.c8.s1.5

The atmospheric agency acts on rocks as follows: The carbon dioxide gas in the atmosphere renders the calcium carbonate soluble. Limestones, chalk and kankar thus get dissolved and become available as plant food, and the rain-water from calcareous rocks charged with calcium carbonate flows into the sea, where shell-fish, corals and foraminifera utilize the lime in building up their own bodies, which in time settle in the form of dead shells and form new rocks. The dew and water-vapour of the atmosphere which get into the interstices of rocks in cold regions are frozen and the resulting expansion disintegrates the particles of rocks. When water freezes, it expands, and the volume of ice formed is increased by nine per cent. This increase in volume exerts a force of 1,640 tonnes per square metre. The oxygen of the atmosphere is a very potent agent in oxidizing and disintegrating the surfaces of hard rocks. Strong currents of wind carry sand and finer particles of matter (such as common salt) from the sea-shore and the dry beds of rivers into the interior.

v1.c8.s1.6

Physical agencies operate in disintegrating soils chiefly in the form of heat. Rocks are poor conductors and hence the effects of heat and cold extend only to a slight depth from the surface. The greater expansion or contraction of the surface produces a strain which causes a layer of rock to break off. Earthquakes, hot springs and volcanoes alter even the superficial layers of the earth's surface.

Action of Plants

v1.c8.s1.t1.1

Disintegration of rocks takes place by hydration, oxidation and physical action. Nitrification then proceeds with the help of bacteria. Lichens and blue-green algae appear. Gradually, the quantity of soil on the hard surface of the rock increases, and the growth of vegetation becomes more vigorous, mosses, liverworts, ferns and grasses gradually taking the place of lichens. When visible soil accumulates, and fissures and cracks appear on the rock, herbs and shrubs multiply and by their root-action further help to disintegrate the rock to some depth. The formation of soils now goes on apace. Lichens and bacteria are able to draw nourishment from the most insoluble rocks, not only from basalts, granites and schists, but also from quartz. Even quartz gets covered with lichens when exposed long enough to the air. The action of higher vegetation on rocks is partly mechanical and partly chemical. Roots get into the clefts of rocks and tear them asunder. Chemical action is concerned in the solution of some of the ingredients of the rock. The solvent action of roots is partly due to the formation of acids in them which act on the particles of soil.

Action of Animals

v1.c8.s1.t2.1

The larger rodents, like rats, squirrels and rabbits, burrow into the ground and thus large quantities of partially decomposed rocks are exposed to the agencies of weathering. Earthworms and ants also help to decompose and disintegrate the rocks. They carry down vegetable matter, which on decomposition helps to break down the minerals. Earthworms pass large quantities of soil through their bodies. This passage of soil through their bodies amounts to more than 22 tonnes of soil per hectare. This process greatly helps to mix the soil with the subsoil. Worm-casts are particularly useful to the farmer, as they help to loosen and perforate the soil to facilitate the penetration of roots, water and air. These worms also drag down leaves, pieces of straw, etc., into their holes, thus incorporating organic matter into the soil, and making heavy soils lighter and light soils heavier.

v1.c8.s1.t2.2

As the soil particles become smaller, their water-holding capacity increases, as each soil particle is surrounded by a film of capillary water. This water is very effective in the decomposition of the soil particles. Hydration, oxidation and carbonation work simultaneously. These decomposition processes are always accompanied with increases in bulk and these tend to disrupt the rock and further assist to disintegrate it.

Soil Types

v1.c8.s2.1

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

v1.c8.s2.t1.1

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).

v1.c8.s2.t1.2

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.

v1.c8.s2.t1.3

Geologically the alluvium is divided into (i) *khadar*, or new alluvium of

v1.c8.s2.t1.4

INDIA SOIL MAP

v1.c8.s2.t1.5

v1.c8.s2.t1.6

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.

v1.c8.s2.t1.7

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.

v1.c8.s2.t1.8

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.

v1.c8.s2.t1.9

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.

v1.c8.s2.t1.10

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.

v1.c8.s2.t1.11

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.

v1.c8.s2.t1.12

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

v1.c8.s2.t2.1

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.

v1.c8.s2.t2.2

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.

v1.c8.s2.t2.3

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.

v1.c8.s2.t2.4

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.

v1.c8.s2.t2.5

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.

v1.c8.s2.t2.6

The black soils of Karnataka are fairly heavy, with a high salt concentration. They are generally rich in lime and magnesia.

Red Soils

v1.c8.s2.t3.1

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.

v1.c8.s2.t3.2

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.

v1.c8.s2.t3.3

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.

v1.c8.s2.t3.4

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.

v1.c8.s2.t3.5

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.

v1.c8.s2.t3.6

The predominant type in the eastern tract of Karnataka is the red soil overlying granite. It is rich in potash, iron and alumina.

v1.c8.s2.t3.7

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

v1.c8.s2.t4.1

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.

v1.c8.s2.t4.2

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.

v1.c8.s2.t4.3

Fig. 5. The Indo-Gangetic plain in the Punjab has a rich alluvial soil, which produces bumper crops of wheat and rice

v1.c8.s2.t4.4

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

v1.c8.s2.t4.5

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

v1.c8.s2.t4.6

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

v1.c8.s2.t4.7

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.

v1.c8.s2.t4.8

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.

v1.c8.s2.t4.9

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.

v1.c8.s2.t4.10

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.

v1.c8.s2.t4.11

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.

v1.c8.s2.t4.12

In West Bengal, the area between the Damodar and the Bhagirathi is interspersed with some basaltic and granitic hills with a laterite capping.

v1.c8.s2.t4.13

In Bihar, the laterite occurs principally as a cap on the higher plateau, but is also found in fair thickness in some valleys.

v1.c8.s2.t4.14

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

v1.c8.s2.t5.1

In addition to the four principal groups of soils described above, mention may be made of four more groups.

v1.c8.s2.t5.2

*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.

v1.c8.s2.t5.3

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.

v1.c8.s2.t5.4

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.

v1.c8.s2.t5.5

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.

v1.c8.s2.t5.6

*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.

v1.c8.s2.t5.7

*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.

v1.c8.s2.t5.8

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.

References

v1.c8.s3.1

Birkeland, P.W. *Pedology, Weathering and Geomorphological Research*, New York, 1974 Donahue, R.L. *Our Soils and Their Management*, Bombay, 1963 Gerasimov, I.P. *The Age of Recent Soils*. *Geoderma*, 12, 1974 Krishnan, M.S. *Geology of India and Burma*, Madras, 1960 Maignein, R. *Review of Research on Laterites*: UNESCO, natural resources research, IV, 1966 Mukerji, N.G. *Handbook of Indian Agriculture*, Calcuttta, 1915 Randhawa, M.S. *Agriculture and Animal Husbandry in India*, New Delhi 1962 Raychaudhuri, S.P. *Land and Soil*, New Delhi, 1966 Raychaudhuri, S.P. *et al.* *Soils of India* New Delhi, 1963 Sahasrabuddhe, D.L. and Naggehalli, N.N. *Agricultural Geology of India and Physical Properties of Soils*, Poona, 1947 Wadia, D.N. *Geology of India*, 1953