Soil Resources

Terms in soil science

Pedology. A branch of soil science concerning the study of formation, evolution,
morphology and classification of soil.

Pedogenesis. The process of soil formation, influenced by climatic conditions –

temperature, running water, effects of intensity of wind; composition of the parent
rock; topography; vegetation and animal life.

Soil fertility. The strength of the soil to support plant life and vegetation is called
its fertility. Fertile soil has the following characteristics:
- Adequate amount of moisture, to aid in the uptake of dissolved nutrients.
- Sufficient depth to enable the roots to develop fully as per their requirements.
- Adequate amount of essential inorganic nutrients for proper growth –
• Inorganic components like clay and sand, containing minerals like silica,
iron, magnesium, calcium, sodium, potassium, etc.
• Organic component or humus, which is made up of decayed organic
matter such as decomposed vegetal and animal remains, animal waste,
minute bacteria, etc.

Soil texture. It refers to the feel and consistency of the soil with respect to the size
of particles present in it. The kind of particles may be gravel, sand, silt and clay.
- Gravel and sand make the soil coarse and gritty to touch.
- Clay makes the soil sticky and plastic when wet. It makes a smooth, thin,
continuous smear when rubbed between fingers, but is difficult to crush when
dry.
- Silt (soil carried by the rivers and deposited on the banks and in deltas) also
makes a smooth smear when rubbed between fingers, but does not thin out like
clay, before becoming rough and broken.

In-situ soil. Residual, sedimentary or ‘in situ’ soils are found where they were
originally formed by the breaking up of parent rocks; e.g.: black soil, red soil, laterite
soil, etc.

Ex-situ soil. Transported or ‘ex situ’ soils are translocated from the place of
formation to a different place by agents of gradation like running water, wind, etc.;
e.g.: alluvial soil, loess, etc.
Soils in India
Alluvial soil.
Formation These soils are formed by the deposition of the river load as it flows
from its upper to its lower course, constituting very fine particles of
soil called alluvium, brought down as sediments.
It is the only ex-situ soil in India.
Alternative Riverine soil, as they are mainly found in the river basins.
names
Types Bhangar Khadar
These are older alluvium soils. These are newer / younger
alluvium soils, as they are
frequently inundated and
replenished by floods during
monsoons.
They are not very fertile. They are very fertile and ideal for
intensive cultivation.
They are found higher up in the They are found in the lower
northern plains, above the flood levels in the flood plains near the
levels of rivers (30m above sea rivers and in deltas.
level) and presents a terrace-like
structure.
They contain kankars (lime They contain fine silt, sand and
nodules), pebbles and gravels. clay (this mixture is called
loam).
They are clayey and non-porous. They are loamy and porous.
They are darker in colour, They are lighter in colour,
ranging from light grey to ash varying from yellowish to pale
grey. brown.
Distribution Inland o Plains of the Indus, Ganga and Brahmaputra
Alluvium rivers;
o Extending from Punjab and Sindh, Pakistan to
Assam and Bangladesh;
o A part of Gujarat and a few patches in Rajasthan.
Deltaic Extensive tracts of the Indus-Ganga-Brahmaputra
Alluvium deltas (West Bengal and Odisha).
Coastal o Along the coastal strips of Peninsular India;
Alluvium o Occupying the coasts of Godavari, Krishna,
Kaveri, Narmada and Tapi;
o Plains of Gujarat.
Colour • Varies from light grey to deep black.
• The soil of the upper Ganga valley is faint yellow.
• The soil of the Godavari and Krishna valley is dark brown as
these rivers flow over black soil.
• Also depends on the type of alluvium [Refer ‘Types’].
 Texture • Coarsest, large and non-uniform in the upper course of the river
(near the place of the origin, in piedmont plains); medium in
the middle course; and finest and moist in the lower course.
• Alluvium of the upper Ganga valley is dry, porous, sandy, and
consists of clay and organic matter, while that of lower Ganga
valley is more compact, finer and moister and that of the
Godavari and Krishna valley is non-porous and clayey.
• Usually light and porous, and therefore easily tillable.
Composition • Rich in potash and lime.
• Deficient in nitrogen and humus; except in the Ganga deltaic
alluvium, which is rich in humus.
• Tends to be phosphoric, except in the Ganga deltaic alluvium,
which lacks phosphorus.
• Soil in the drier areas is more alkaline.
Fertility Alluvial soils are very fertile and agriculturally the most important.
They support the maximum share of agricultural products (both
rabi and kharif) and the bulk of Indian population.
Associated • Rice, wheat, sugarcane, cotton, tobacco, oilseeds.
crops • Also useful for jute cultivation in the lower Ganga-Brahmaputra
valley.

Black soil.
Formation After the solidification of basic lava erupted during volcanic activity,
volcanic rocks (basalt) are originated, which undergo denudation to
develop black soil. It is an in-situ soil.
Alternative • Regur soil, from Telugu word Reguda.
names • Black Cotton Soil as cotton thrives on this soil.
• Volcanic/lava soil as it is formed by the denudation of basalt.
Distribution • Vastly confined to the Deccan Trap region, which includes
Maharashtra, Gujarat, western M.P., A.P., etc.
• It is also found in parts of Gujarat, the northern parts of
Karnataka and Telangana and southern districts of Tamil Nadu.
Colour Varies from medium black to deep black to chestnut brown. The
black colour is due to the crystalline metamorphic rocks like schists
and basic gneiss.
Texture Very clayey and fine-grained.
• Because of the high clay content, these soils have a great ability
to retain moisture for a long duration.
• Moreover, during dry conditions, black soils shrink and develop
big cracks which help in aeration (self-ploughing quality).
• When wet, these soils expand, become sticky and difficult to
work with. Hence, the soil needs to be tilled after the first rains.
Composition • Up to 50% of clay.
• No gravel or sand.
• Rich in lime, iron, magnesium, calcium carbonate, alumina and
potash.
 • Deficient in phosphorus, nitrogen and humus.
Fertility • Highly fertile in most of the places, even without using
fertiliser.
• High retentivity of moisture makes it suitable for dry farming
too.
Associated Cotton, wheat, jowar, sugarcane, Virginia tobacco, linseed, gram,
crops sunflower, fruits and vegetables.

Red soil.
Formation Under prolonged weathering by rainfall, ancient crystalline igneous
and metamorphic rocks of the Peninsular plateau, including acid
granites and gneisses, break up to form these soils.
It is an in-situ soil.
Distribution • They practically encircle the entire black soil region on all sides.
• They cover almost the whole of Tamil Nadu, large parts of
southern and eastern Karnataka, NE part of A.P., SE
Maharashtra, parts of Odisha, Chhattisgarh, in the
Chotanagpur plateau region in Jharkhand, parts of Meghalaya,
Mizoram, Manipur, Telangana and Nagaland.
• Scattered patches are also found in West Bengal, U.P. and
Rajasthan.
Colour • Generally red, due to the presence of iron oxides.
• At several places, their colour varies from red to brown, grey or
chocolate, depending on parent rocks and climate.
• They look yellow when they occur in a hydrated form.
Texture It is coarse, friable, crumbly and porous. It is thicker in the plain
areas than on the slopes.
Composition • Rich in potash and iron oxides.
• Deficient in phosphorus, nitrogen, magnesium, potassium,
lime and humus.
Fertility • It is mostly infertile, but on application of fertiliser and
irrigation, it gives excellent yield.
• Its productivity increases with regular use of fertilisers.
• It is usually deep and comparatively more fertile in lowlands
than in highlands, where it is thin and poor.
• It is ideal for dry farming as it does not require much moisture
and it is formed in areas with scanty rainfall.
(Dry farming is the method of farming adopted in certain
regions of inadequate rainfall and devoid of irrigation facilities
by conserving moisture in the soil and by raising drought-
enduring crops.)
Associated • Vegetables, rice, wheat, ragi, tobacco.
crops • Groundnut and potatoes can be grown on coarse soils at higher
levels.
• Sugarcane can be grown on heavy clays at lower levels.
Laterite/lateritic soil.
Formation It is an in-situ soil.
• They are formed as a result of atmospheric weathering of rocks
under conditions of high rainfall and temperature with
alternate wet and dry periods, i.e., strictly under monsoon
conditions.
• They are formed by leaching due to tropical rains.
(Leaching/desilication is the process in which the nutrients like
silica and lime in the top soil are washed away and get
percolated down below the soil by heavy rainfall, thus leaving
the top soil infertile.)
Types • Upland laterites are formed over hills and uplands.
• From there, the upland laterites are transported by streams
towards lowlands, where they are called lowland laterites.
Distribution • Highlands of the peninsular plateau, i.e., summits of the
Sahyadris, Eastern Ghats, Rajmahal Hills and many other hills.
• Patches are found in M.P., Odisha, Maharashtra, West Bengal,
A.P., Telangana, Karnataka, Kerala, Tamil Nadu, etc.
Colour Red in colour due to the presence of iron oxide, which is formed by
leaching (soluble constituents like potash are removed, leaving
behind alumina and iron oxides).
Texture Generally coarse in texture, soft, friable and porous in nature.
Composition • Poor in lime, magnesium and phosphoric acid and deficient in
potash, nitrogen and silica.
• Rich in iron.
• Acidic in nature as the alkalis are leached.
Fertility • Because of high acidity, low moisture retention and removal of
essential nutrients by leaching, laterite soils have low fertility.
• However, they have a unique property of hardening and
becoming more durable when exposed to air. Thus, they are
considered valuable for building material.
Associated • Manuring and other activities are required to make them
crops suitable for growing crops such as ragi, rice and sugarcane.
• Usually, special crops like tapioca, cashew nut, etc. are grown.
• Some plantation crops like tea, coffee, rubber, coconut, etc. can
be grown on higher elevations with application of fertilisers and
irrigation.
• Paddy can be grown on lower elevations.

Soil Erosion
Meaning. The removal of the top soil cover by different agents of weathering, such
as running water, wind, human activities, overgrazing by animals, etc. is called soil
erosion. Generally, there is a balance between the soil forming process and the
erosional process of running water and wind. If the balance is disturbed by natural or
human factors there is a greater rate of removal of soil and the entire soil layer may be
removed in a few years.

Erosion by running water.

Sheet • It occurs during heavy rainfall, in areas where vegetation is
erosion destroyed, when the rainwater, instead of sinking, stimulates the
erosive power and a surface film of water washes away a thin
layer of top soil on the surface.
• It is a harmful process of eating away the finer and more fertile
top soil.

Rill Erosion • When sheet erosion continues for long enough, the slit-laden
run-off forms many small finger-like rills or groves over a large
area of the landscape.
• Eventually, the fine rills increase in number, deepen and widen,
reducing the cultivable area of land.
• It is an intermediate stage between sheet and gully erosion.
Gully • When there is heavy downpour on the steep slopes, the bare soil
Erosion is removed by water running off along definite paths down the
slope or in channels, and deep steep-sided gullies are made.
• It removes nutrients and heavy load of loose soils, making the
soil unproductive and water muddy.
• A region having a large number of deep gullies or ravines that cut
up agricultural land into uncultivable land is called a bad-land,
e.g.: Chambal valley in M.P.
Sea / Shore • The tidal waves of the sea cause considerable damage to the soil
Erosion along the coast.
• The powerful waves dash against the coast, break hanging cliff
rocks, and then while retreating, remove the broken material.
• It is frequent throughout the eastern and western coasts of India.
Stream • The banks of the streams and rivers get eroded by the continuous
Bank flowing of water.
Erosion • Streams and banks change their courses by cutting one bank and
depositing the silt loads on the other. During flash floods, it takes
a serious form and the bed of the river gradually widens.
• It is prevalent in the flood plains of Ganga, Yamuna and other
rivers.

Erosion by wind.
- On extensive flat lands subject to windy dry season, such as in deserts, semi-
deserts, etc., soil devoid of vegetation is exposed to wind of high velocity.
- The wind blows away the loose soil particles, especially fine particles of sand,
and deposits them elsewhere, rendering both the areas unproductive.
- Wind moves soil particles of 0.1-0.5mm in size in a bouncing or hopping fashion
(saltation) and those greater than 0.5mm by rolling (soil creep). The particles
 less than 0.1mm detach into suspension, during which wind erosion is most
visible as dust storms.
- Wind erosion decreases the productive capacity of the soil, as most of the
required nutrients are carried away by the wind.

Erosion due to human action.

- With rising population increases the demand for land and natural resources.
Consequently, indiscriminate deforestation occurs and the natural vegetation
cover is removed. This loss of vegetation cover leads to sheet erosion, then rill
erosion and finally gully erosion, due to surface water run-off.
- Faulty agricultural practices such as:
• shifting agriculture,
• lack of crop rotation,
• traditional ploughing methods in the up-and-down manner along the
slopes,
• small size of landholdings,
• absence of terracing, contour farming and improper use of manure, etc.;
makes it easier for the soil to be carried away by wind and running water.
- Construction work, digging of mines, blasting near terrain to make new
roadways also contribute to soil erosion.

Erosion due to overgrazing. Uncontrolled grazing of domestic animals in the

valleys and upper slopes results in the removal of grass over a large area, loss of
vegetation cover and the subsequent exposure of the soil to wind and water erosion.

Soil erosion in India.

- Among the states, Rajasthan comes on the top of soil eroded regions, followed
by M.P., Maharashtra, U.P., Gujarat, A.P. and Karnataka.
- In the outer Himalayas and in the piedmont zone of the western Himalayas,
destruction of vegetation is the main cause of soil erosion. The debris coming
down the slopes choke up the rivers and cause floods. The sediments get
deposited on the fertile land.
- The banks of the rivers, especially Yamuna, Chambal, Mahi, Sabarmati, etc. are
badly affected by soil erosion. Large areas of agricultural land in the states of
U.P., M.P, Rajasthan and Gujarat have been transformed into ravines and
gullies. These are called Badlands.
- In the NE Region of India (Assam, West Bengal), heavy rains, floods and stream
bank cutting are the main causes of erosion.
- Arid areas of Rajasthan and southern Punjab like Kota, Bikaner, Jodhpur,
Bharatpur and Jaipur are subject to severe soil erosion by wind action.
- In the hills of South India (Nilgiris), steep slopes, heavy rainfall and defective
methods of cultivation are responsible for the soil erosion.

Prevention of soil erosion.

Afforestation Planting trees on hill slopes and river valleys and increasing land
area under forest cover is the best way to prevent soil erosion by the
 roots holding the soil tightly together, as well as to enhance the
water-retentivity of the soil.
Restriction in Overgrazing of forests and grasslands by domestic animals should
overgrazing be checked. Animals should be moved over different pastures and
should be allotted specific timings so as avoid the removal of all
vegetation from the ground.
Improved Terrace • It is the cutting up of slopes into a series of large
farming farming steps called terraces having a horizontal top and
techniques (Hilly areas) steep slopes at the back and front.
• The terraces act as bunds and prevent the soil
from being washed away by running water by
controlling the direct flow of water down the
slope.
Contour • It involves ploughing along the contours on the
ploughing slope of the field in a circular manner, beginning
(Hilly areas) from the outer edge.
• It prevents the soil from being washed away by
rainwater or by surface run-off.
Strip • Strip cropping is the planting of different kinds
cropping of crops in alternate strips of land.
(Plains and • It checks the impact of the winds.
arid areas)
Crop It increases the fertility of the soil by replenishing
rotation nutrients.
(Arid areas)
Cover crops Planting of cover crops can check the soil erosion as
plant roots hold the soil together.
Constructing • Bunds are low mud walls or embankments that
bunds help to obstruct the flow of water.
(Hilly areas) • Constructing bunds across hill slopes and field
boundaries is effective in reducing soil erosion.
Shelter Belts of trees and shrubs should be planted to check the velocity of
belting wind where wind erosion is prevalent. These belts are, therefore,
(Arid areas) also called wind breaks.
Construction Dams can be built in the upper course of rivers to control the velocity
of dams of running water and therefore check soil erosion.
Plugging In it, the gullies made in the soil are plugged with deposition of silt
gullies during heavy rains.
Banning Primitive methods of farming such as shifting agriculture,
primitive jhumming or slash-and-burn type of agriculture must be legally
agricultural banned.
methods
Soil conservation
Meaning. Soil conservation is an effort, made by man, towards the prevention of
loss of the topsoil by soil erosion and the prevention of reduction in its fertility caused
by over-usage, acidification, salinisation, etc. and its retainment.

Need.
Soil erosion has adverse effects:
- Loss of fertile top soil together with its nutrients from the upper surface, leading
to the gradual loss of soil fertility and agricultural productivity.
- Lowering of the underground water table and decreasing of soil moisture.
- Drying of vegetation and extension of arid lands. Increased frequency of
droughts and floods.
- Silting of river and canal beds.
- Recurring landslides.
- Deterioration of economic and cultural development.