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BIO-GEOGRAPHY
Soil can be defined as the solid material on the Earth's surface that results from the interaction of weathering
and biological activity on the parent material or underlying hard rock.
The naturally occurring soil is influenced by parent material, climate relief, and the physical chemical and
biological agents (micro-organisms) in it.
A soil is made up of four elements: inorganic fraction (derived from the parent material), organic material, air
and water. The abundance of each component and its importance in the functioning of the soil system vary
from horizon to horizon and from one soil to another.

Soil Characteristics
Soil Texture
- Soil texture is a term used to describe the distribution of the different sizes of mineral particles in a soil.
- Textures range from clay, sand, and silt at the extremes, to a loam which has all three sized fractions
present. The main influence of texture is on permeability which generally decreases with decreasing
particle size.
- A clayey soil may thus be described as fine, a sandy soil as course, while a silty soil is intermediate.
- The standard unit for the measurement of soil particles is the millimeter, but a smaller unit is the micron
(1 micron = 0.01 mm), which is applicable, for instance, to the measurements of soil colloids.
Soil Air
- The air content of a soil is vital, both to itself and to organic life within it. A certain amount of air is
contained between the individual particles except for the waterlogged soils. The air in the soil helps in the
process of oxidation which converts part of the organic material into nitrogen in a form readily available
to the plants.
- On the other hand too high degree of oxidation (in the tropical lands) may consume so much organic
material that the soil becomes increasingly sterile.
Soil water
- Depending on the texture of the soil, water moves downward by percolation. The amount of water in the
soil varies from almost nil in arid climates which makes life virtually impossible for organisms, to a state
of complete water logging which excludes all air, causes a reduction of bacteriological activity, and limits
decomposition.
- In damp climates, especially in high latitudes where the evaporation rate is low, water tends to move
predominantly downward, particularly in coarse-grained sandy soils. This dissolves the soluble minerals in
the soil, together with soluble humus material and carries both downward, a process called leaching or
eluviations.
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- A typical leached soil is known as podzol, a Russian word meaning ash because the surface layer is often
grayish or ash-coloured.
- In a hot, arid climate, evaporation exceeds precipitation for greater part of the year, so the water tends
to move upward and the soil dries out. Consequently, in some areas, a thin salty layer is formed on the
surface. This process of Stalinization can produce an extremely saline soil known as reh or kallar.
Soil colour
- Generally soil colour is determined by the amount of organic matter and the state of the iron. Soil colour
is also related to soil drainage, with free draining, well AERATED soils (with pore space dominated by
oxygen) having rich brown colours.
- In contrast, poorly draining soils, often referred to as gleys, develop under ANAEROBIC conditions (the
pore space dominated by water) and have grey or blue-grey colours.
- Soils with periodic waterlogging are imperfectly drained and are often highly mottled with blotches of
contrasting colour. MOTTLES are often rusty in colour and are due to iron concentration.
- Such colours are the result of oxidation-reduction; iron is the main substance affected by these processes.
If the iron is released in an anaerobic environment, then it stays in the reduced state giving it the grey
blue colour of waterlogged soils

Factors Responsible for Soil Formation

Soil formation is the combined effect of physical, chemical, biological, and anthropogenic processes on soil
parent material.

a) Parent material
- This is the material from which the soil has developed and can vary from solid rock to deposits like
alluvium and boulder clay. It has been defined as 'the initial state of the soil system'.
- The parent material can influence the soil in a number of ways: colour; texture; structure; mineral
composition and permeability/drainage.
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- Soil may form directly by the weathering of consolidated rock in situ (a residual soil), saprolite (weathered
rock), or it may develop on superficial deposits, which may have been transported by ice, water, wind or
gravity. These deposits originated ultimately from the denudation and geologic erosion of consolidated
rock. Consolidated material is not strictly parent material, but serves as a source of parent material after
some physical and /or chemical weathering has taken place.
- Soils may form also on organic sediments (peat, muck) or salts (evaporites). The chemical and mineralogical
compositions of parent material determine the effectiveness of the weathering forces.
- During the early stages of soil formation, rock disintegration may limit the rate and depth of soil
development. The downward movement of water is controlled largely by the texture of the parent
material. Furthermore, parent material has a marked influence on the type of clay minerals in the soil
profile.
b) Climate
- Temperature varies with lattitude and altitude, and the extent of absorption and reflection of solar
radiation by the atmosphere. Solar radiation (direct radiation and diffuse radiation) increases with elevation,
differs seasonally, and is influenced by cloud cover or other atmosperic disturbance (e.g. air pollution). The
absorption of the solar radiation at the soil surface is affected by many variables such as soil color,
vegetation cover, and aspect. In general, the darker the soil color, the more radiation is absorbed and the
lower the albedo. The effect of vegetative cover on absorption varies with density, height, and color of
the vegetation. Hence the absorption differs in areas with decidious trees (soil surface is shaded by trees
most of the year) and arable land (soil surface is not shaded throughout the year).
- Light, or whitish-colored, soil surfaces tend to reflect more radiation. When incoming solar radiation is
reflected, there is less net radiation to be absorbed and heat the soil. Snow is especially effective in
reflecting the incoming solar radiation.
- Soil moisture also controls the heating up or cooling down of soils. Water has a high specific heat capacity
(1 cal g-1 C), whereas dry soils have a specific heat capacity of about 0.2 cal g-1 C. This means that sandy
soils cools and heats more rapidly than soils high in silt or clay. Once a wet soil is warmed, it takes longer
to cool than a dry soil.
- In the Northern Hemisphere, south-facing slopes tend to be warmer and thus more droughty than north
facing slopes.
- Temperature affects the rate of mineral weathering and synthesis, and the biological processes of growth
and decomposition. Weathering is intensified by high temperatures, hence weathering is stronger in the
tropics than in humid regions.
- Temperature also influences the degree of thawing and freezing (physical weathering) in cold regions.
- Biological processes are intensified by rising temperatures. Reaction rates are roughly doubled for each
10°C rise in temperature, although enzyme-catalysed reactions are sensitive to high temperatures and
usually attain a maximum between 30 and 35 °C.
c) Biological Factors
- The soil and the organisms living on and in it comprise an ecosystem. The active components of the soil
ecosystem are the vegetation, fauna, including microorganisms, and man.
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• Vegetation:
- The primary succession of plants that colonize a weathering rock culminates in the development of a
climax community, the species composition of which depends on the climate and parent material, but
which, in turn, has a profound influence on the soil that is formed.
- Deciduous forest seems to accelerate soil formation compared to grassland on the same parent material
under similar climatic conditions.
- Differences in the chemical composition of leaf leachates can partly account for a divergent pattern of
soil formation. For example acid litter of pines or heat favors the development of acid soils with poor soil
structure, whereas litter of decidous trees favors the development of well structured soils.
• Meso-/Macrofauna:
- Earthworms are the most important of the soil forming fauna in temperate regions, being supported to a
variable extent by the small arthropods and the larger burrowing animals (rabbits, moles).
- Earthworms are also important in tropical soils, but in general the activities of termites, ants, and beetles
are of greater significance, particularly in the sub humid to semiarid savanna of Africa and Asia.
- Earthworms build up a stone-free layer at the soil surface, as well as intimately mixing the litter with fine
mineral particles they have ingested.
- The surface area of the organic matter that is accessible to microbial attack is then much greater. Types
of the mesofauna comprise arthropods (e.g. mites, collembola) and annelids (e.g earthworms, enchytraeids).
• Microorganisms:
- The organic matter of the soil is colonized by a variety of soil organisms, most importantly the
microorganisms, which derive energy for growth from the oxidative decomposition of complex organic
molecules.
- During decomposition, essential elements are converted form organic combination to simple inorganic
forms (mineralization).
- Most of the microorganisms are concentrated in the top 15 - 25 cm of the soil because carbon substrates
are more plentiful there. Estimates of microbial biomass C range from 500 to 2,000 kg /ha to 15-cm depth
(White, 1987).
- Types of microorganisms comprise bacteria, actinomycetes, fungi, algae, protozoa, and soil enzymes.
• Man:
- Man is perhaps now the most influential of all organisms. He affects the soil by such activities as: plowing,
irrigating, mining, clearing, disposing and leveling.
- The effects of vegetation on soil formation are very profound. Different soils form in a grassland than
under a forest. Much of this difference is due to the rapid nutrient cycling in grasslands.
- Vegetation effects extent of cover, thereby influencing runoff and erosion. Vegetation type and amount
directly influences the type and amount of organic matter accumulation on the soil, and thereby influences
such soil chemical properties as pH and nutrient supply.
- Finally, vegetation is the food source for most microorganisms so the vegetation exerts a strong influence
on soil microbial populations.
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d) Time
- Time is a factor in the interactions of all the above factors as they develop soil. Over time, soils evolve
features dependent on the other forming factors, and soil formation is a time-responsive process dependent
on how the other factors interplay with each other.
- Soil is always changing.It takes about 800 to 1000 years for a 2.5 cm thick layer of fertile soil to be
formed in nature. For example, recently-deposited material from a flood exhibits no soil development
because there has not been enough time for soil-forming activities. The soil surface is buried, and the
formation process begins again for this soil. The long periods over which change occurs and its multiple
influences mean that simple soils are rare, resulting in the formation of soil horizons. While soil can
achieve relative stability in properties for extended periods, the soil life cycle ultimately ends in soil
conditions that leave it vulnerable to erosion. Despite the inevitability of soil retrogression and degradation,
most soil cycles are long and productive.
- Soil-forming factors continue to affect soils during their existence, even on "stable" landscapes that are
long-enduring, some for millions of years. Materials are deposited on top and materials are blown or
washed away from the surface. With additions, removals and alterations, soils are always subject to new
conditions. Whether these are slow or rapid changes depend on climate, landscape position and biological
activity.
e) Relief
- Relief is not static; it is a dynamic system (its study is called geomorphology). Relief influences soil
formation in several ways:
• It influences soil profile thickness i.e. as angle of slope increases so does the erosion hazard.
• It has an effect on climate which is also a soil forming factor.
• Gradient affects run-off, percolation and mass movement.
• It influences aspect which creates microclimatic conditions.

Stages of Soil Formation

Soil formation is a long slow process. It's estimated that an inch of soil takes 500 to 1000 years to form. Soil
is constantly being formed. It is also constantly being eroded.
• Stage One
- This is the rock pulverizing stage. Here the forces of wind, rain, freezing and thawing water, earthquakes,
volcanos all work to slowly pulverize rocks into smaller particles that can make up a soil.
- At the end of this stage a combination of sand, silt and clay sized particles forms. These form a mineral
soil like substance but are unable to support life.
- They are missing nitrogen. It may seem nitrogen should be the least of a being's worries. After all the air
we breath is made up of about 78% nitrogen gas. The problem is that plants can not use nitrogen in this
form. For them it needs to be converted to either ammonia which is a combination of nitrogen and
hydrogen or nitrates - a combination of nitrogen and oxygen.
• Stage Two
- This is the early stage of soil formation. Here life is added specifically by lichens.
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- Lichens are a symbiotic relationship of algae and fungus. The algae has the very important role of fixing
the nitrogen, changing it from nitrogen gas to a form, the plant can use. It also captures the sunlight and
creates sugars and oxygen. The fungus provides a place for the algae to live, along with water and the
mineral nutrients it needs.
- Lichens are very long lived - hundreds to thousands of years and they also further break down rock with
acids they produce. About 8% of the earth is covered by lichens.
- Lichens are joined by mosses, bacteria, protozoa, and fungi. These form a complex cooperative community
that works to store nitrogen, nutrients and water to foster the growth of new plants.
• Stage Three
- At this time the little pockets of soil have formed to the extent that some larger plants, plants with roots
can have a go at growing.
- The first pioneers will be short lived but as their bodies are added to the layers of soil forming, the soil
becomes more capable of supporting life. Humus builds and soil horizons begin to form.
• Stage Four
- The soils are developed enough to support thick vegetation.

Soil Forming Processes

The four major processes that change parent material into soil are additions, losses, translocations, and
transformations.
• Additions
- The most obvious addition is organic matter. As soon as plant life begins to grow in fresh parent material,
organic matter begins to accumulate. Organic matter gives a black or dark brown color to surface layer.
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Most organic matter additions to the surface increase the cation exchange capacity and nutrients, which
also increase plant nutrient availability.
- Other additions may come with rainfall or deposition by wind, such as the wind blown or eolian material.
On the average, rainfall adds about 5 pounds of nitrogen per acre per year. By causing rivers to flood,
rainfall is indirectly responsible for the addition of new sediment to the soil on a flood plain.
• Losses
- Most losses occur by leaching. Water moving through the soil dissolves certain minerals and transports
them into deeper layers. Some materials, especially sodium salts, gypsum, and calcium carbonate, are
relatively soluble. They are removed early in the soil's formation. As a result, soil in humid regions
generally does not have carbonates in the upper horizons. Quartz, aluminum, iron oxide, and kaolinitic
clay weather slowly. They remain in the soil and become the main components of highly weathered
soil.
- Fertilizers are relatively soluble, and many, such as nitrogen and potassium, are readily lost by leaching,
either by natural rainfall or by irrigation water. Long- term use of fertilizers based on ammonium may
cause acidity in the soil and contribute to the loss of carbonates in some areas.
- Oxygen, a gas, is released into the atmosphere by growing plants. Carbon dioxide is consumed by growing
plants, but lost to the soil as fresh organic matter decays. When soil is wet, nitrogen can be changed to
a gas and lost to the atmosphere.
- Solid mineral and organic particles are lost by erosion. Such losses can be serious because the material lost
is usually the most productive part of the soil profile. On the other hand, the sediment relocated to lower
slope positions or deposited on bottom lands has the potential to increase or decrease productive use of
soils in those areas.
• Translocations
- Translocation means movement from one place to another. In low rainfall areas, leaching often is incomplete.
Water starts moving down through the soil, dissolving soluble minerals as it goes. There isn't enough
water, however, to move all the way through the soil. When the water stops moving, then evaporates, salts
are left behind. Soil layers with calcium carbonate or other salt accumulations form this way. If this cycle
occurs enough times, a calcareous hardpan can form.
- Translocation upward and lateral movement is also possible. Even in dry areas, low-lying soils can have
a high water table. Evaporation at the surface causes water to move upward. Salts that are dissolved in
solution will move upward with the water and deposit on the surface as the water evaporates.
• Transformations
- Transformations are changes that take place in the soil. Microorganisms that live in the soil feed on fresh
organic matter and change it into humus. Chemical weathering changes parent material. Some minerals
are destroyed completely. Others are changed into new minerals. Many of the clay-sized particles in soil
are actually new minerals that form during soil development.
- Other transformations can change the form of certain materials. Iron oxides (ferric form) usually give soils
a yellowish or reddish color. In waterlogged soils, however, iron oxides loose some of their oxygen and
are referred to as being reduced. The reduced form of iron (ferrous) is quite easily removed from the soil
by leaching. After the iron is gone, generally the leached area has a grayish or whitish color.
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- Repeated cycles of saturation and drying create a mottled soil (splotches of colored soil in a matrix of
different color). Part of the soil is gray because of the loss of iron, and part is a browner color where the
iron oxide is not removed. During long periods of saturation, gray lined root channels develop. This may
indicate a possible loss of iron or an addition of humus from decayed roots.

Soil Profiles and Horizons

- Soil formation begins with the breakdown of rock into regolith. Continued weathering and soil horizon
development process leads to the development of a soil profile, the vertical display of soil horizons.

- The top layer of the profile is the O horizon which is composed of organic matter. Decomposition of
organic matter enriches the soil with nutrients (nitrogen, potassium, etc.), aids soil structure (acts to bind
particles), and enhances soil moisture retention.

- Next layer is the A horizon in which organic material mixes with inorganic products of weathering. The
A horizon typically is dark coloured horizon due to the presence organic matter.

- Eluviations, the removal of inorganic and organic substances from a horizon by leaching occurs in the A
horizon due to the downward movement of soil water.

- The E horizon generally is a light-colored horizon with eluviation being the dominant process. Leaching
or the removal of clay particles, organic matter, and/or oxides of iron and aluminum is also active in E
horizon.

- The E horizon has a high concentration of quartz under coniferous forests, giving the horizon an ash-gray
appearance.

- The B horizon is a zone of illuviation where downward moving, especially fine material, is accumulated.
The accumulation of fine material leads to the creation of a dense layer in the soil.

- Eluviation is significant in humid climates where ample precipitation leads to the downward movement
of minerals in the soil.

- Illuviation are found closer to the surface in semiarid and arid climates where precipitation is scarce
because due to capillary action cations like calcium and sodium dissolved in soil moves upward.

- The C horizon represents the soil parent material, either created in situ or transported into its present
location. Beneath the C horizon lays bedrock.

Soil Classification
Soil Classification concerns the grouping of soils with a similar range of properties (chemical, physical and
biological) into units that can be geo-referenced and mapped.

- Soils are divided into: (i) zonal, (ii) intrazonal, (iii) azonal categories.

(i) Zonal

- A soil whose characteristics are dominated by the influence of climate and vegetation is known as a zonal
soil. These soils occur on gently undulating land where drainage is free and where the parent material is
of neither extreme texture nor chemical composition. They occur in latitudinal zones.
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(Soil Profiles and Horizons)

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There are seven main types of zonal soils:

• Tundra Soils:
- These soils extend over the tundra region, covering northern parts of North America, southern fringes of
Greenland and northern Eurasia. The exact character of these soils depends on the ground ice position,
slope and the vegetation. If the slope is stable, peaty soils are formed due to slow organic and chemical
action. In case of steep slopes, thin soils result.
- In case the vegetation is absent, ‘ahumic soils’ are formed, like brown polar desert soils of Antarctica. In
forested regions, brown forest soils of Arctic are formed. These soils are brown due to the glacial alluvial
deposits and have a thick, organic horizon-A. The tundra soils generally have poorly developed horizons
as there is no downward movement of moisture.
• Podzols:
- These soils occur south of the tundra region in North America, northern Europe and Siberia and are
associated with conifers and heath plants. In these soils, the horizon-A is colloidal and humus rich, horizon-
E is bleached and ash- grey, horizon-B is brown clayey. Depending on the composition of horizon-B, the
soils could be humus- podzol, iron-podzol or gley podzol. These soils are generally infertile and require lime
and fertilisers if put to agricultural use.
• Brown Forest Soils:
- These soils occur south of the podzol region in milder climates of eastern to USA, northern Europe and
England. These soils are associated with deciduous forests and derive their brown appearance from the
equitable distribution of humus and sesquioxides. There is less leaching, because there is no downward
movement of sesquioxides. The brown forest soils are generally less acidic.
• Lateritic Soils/Latosols/Ferralsols:
- These soils cover large areas of Asia, Africa, South and Central America and Australia. These soils are
generally associated with tropical and sub-tropical climates with a short wet and long dry season and thick
vegetation.
- During the dry season, in these areas, there is intense physical and chemical weathering and organic
activity. During the wet season, an intense leaching causes washing down of humus, organic and mineral
colloids, clay and other soluble material. The upper horizons are, as a result, acidic with minimum organic
content.
- The insoluble oxides of iron and aluminium give the upper layers a characteristic red colour. The lower
horizons are clayey. The lateritic soils are generally poorly differentiated but have deep horizons and are
suitable for mining. These soils are generally infertile due to low base status.
• Chernozem/Prairie/Steppe:
- These soils are associated with grasslands receiving moderate rainfall in northern USA, the Commonwealth
of Independent States (former USSR), Argentina, Manchuria and Australia.
- The chernozems are characterised by high mineral content and low organic content. Calcium carbonate is
quite high in the profile. The upper horizons are dark, mineral-matrix-base rich. The humus content is
around 10%. The parent material of chernozems may be ‘loess’ (wind eroded sediments). The soft, crumb
structure imparts fertility to these soils.
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- The chestnut soils occur on the arid side of chernozems, and are associated with low-grass steppe. The
lime content is still higher in these soils compared to the chernozems.
- The prairies represent the transitional soils between chernozems and the brown forest soils and reflect the
element of increasing wetness. These soils are characterised by less leaching, no calcium content and
taller, coarser grasses. In the corn regions of the USA, prairie soils are quite fertile.
• Grumusols/Reddish Brown Soils:
- These are dark clayey soils of savanna grasslands which occur on the drier margins of the laterites. These
regions experience warm climate with wet-dry seasons. There are no eluviated and alluvial horizons but
the wholesolum is base-rich which gives these soils a dark appearance. These soils support scattered trees,
low scrubs and grasses. During the dry season, these soils show cracks.
• Desert (Seirozems and Red Desert) Soils:
- Seirozems or grey desert soils occur in mid-latitude deserts of Colorado and Utah states of USA, in
Turkmenistan, Mongolia and Sinkiang. These soils occur on the extreme sides of chestnut soils and have
a low organic content. Lime and gypsum are closer to the surface. Being rich in bases, the seirozems are
good for irrigation.

Map Showing the world distribution of major soils.

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- The red desert soils occur in the tropical deserts of the Sahara, West Asia, Pakistan, South Africa and
Australia. These soils are characterised by lack of vegetation and lack of leaching. The insoluble oxides
of iron and aluminium give these soils a red colour. The red desert soils are generally base rich, sandy and
gravelly.
(ii) Intrazonal Soils
- Intrazonal soils is a soil which has been influenced in its development less by climate and vegetation than
by other local factors, such as defective drainage, excessive evaporation or an unusual parent material (such
as lime stone), terrain or age.
- They can be sub-divided into:
• Hydromorphic:
- Surface water gley soils and ground water gley soils are formed under anaerobic conditions. Bog soils are
formed under cool, temperate, continental climates. In these soils the upper layer is peaty while the lower
layer is gleyey. Meadows are formed in mountains and in river basins and have a humus-rich upper layer
and gleyey lower layer.
• Calcimorphic:
- Wherever the limestone is exposed, rendzinas are formed which are dark, organic rich and good for
cultivation in humid regions. The terrarosa soils are formed in the Mediterranean region and are characterised
by insoluble traces of iron and aluminium and low humus besides being clayey.
• Halomorphic:
- These soils occur mostly in deserts. Solonchak are white alkali soils which are formed in depressions and
develop a whitish crust in the dry season. The solonetz are black alkali soils. Intense alkalinisation is
marked by the presence of sodium carbonate. Better drainage results in lighter soils. In solodics, intense
leaching in the presence of sodium results in washing down of clay, colloids, etc., and forms a podzol-like
ashy- grey horizon.
(iii) Azonal Soils
- A soil which has not been sufficiently subjected to soil –forming processes for the development of a
mature profile and so is little changed from the parent rock material.
- Azonal soils do not have B horizon because it is too immature. Thus, the A horizon lies immediately above
the C horizon.
- Examples are soil forming on scress, recently deposited alluvium, sand dunes, and newly deposited glacial
draft, wind-blown sand, marine mud flats and volcanic soils.
- Azonal soils are further divided into: (i) lithosol, (ii) regosol and (iii) entisol (alluvial).

Soil Erosion and Conservation

- Soil erosion has been defined as the gradual removal of the top soil by running water, wind, glacier, sea-
waves, anthropogenic agents and animals.
- Soil erosion is a universal phenomenon.
- According to one estimate about 75, 000 million tonnes of soil is removed by these agents annually.
- In India about 6000 million tonnes of soil is removed annually.
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- Top soil is currently lost 16 to 300 times faster than it can be replaced (which takes 200 to 1000 years).
- Agents of soil Erosion:
• Running water:
1. Uniform removal of soil
2. Rill erosion
3. Gully erosion (e.g. northern Punjab, Haryana, Rajasthan, M.P. U.P)
• Wind Erosion: Mainly in the arid and semi -arid regions.
• Anthropogenic factors: Farmland can be degraded in several other ways besides erosion. Physical degradation
from mechanical tilling can lead to compaction and crusting. Repeated cropping without sufficient fallow
periods or replacement of nutrients with cover crops, manure or fertilizer can deplete soil nutrients. In
addition over application of chemical fertilizers, insecticides and pesticides can kill beneficial soil organism.
- Poor water management on irrigated crop land is a leading cause of degraded farmland.
- Inadequate drainage can lead to water logging of the soil or to Salinization, in which salt levels built up
in the soil to toxic levels. About 15 to 20 percent of the irrigated land is suffering from some degree of
waterlogging and salinization.
Effects of Soil Erosion
a) Loss of fertile top soil leading to gradual loss of soil fertility and agricultural productivity.
b) Loss of mineral nutrients from soil through leaching and flooding.
c) Lowering of the underground water table and decrease in the percentage of soil moisture.
d) Drying of vegetation and extension of arid lands.
e) Increase in frequency of droughts and floods.
f) Silting of river and canal belts.
g) Recurrence of landslides.
h) Adverse effect on economic prosperity and cultural development.
Soil Conservation:
Unchecked soil erosion leads to poverty and reduces the strength of a nation. Some of the important steps
for soil conservation areas under:
1. Rotate soil protecting crops.
2. Application of green and compost manures.
3. Divide agricultural fields into fairly narrow contour strips, wherever possible.
4. Develop terrace channels to carry water off slope to safe waterways.
5. Control gullies by keeping water out of them and check the movement of water in gullies by means of
straw vegetation.
6. Develop a protective vegetation cover in the deserts.
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7. Plant crops in strips at right angles to the principal wind directions on sandy shores.
8. Plant beach grass with wild legumes and nitrogen fixing shrubs.
Soil Conservation Methods: The measures generally adopted for the conservation of soils are:
1. Contour farming
2. Mulching
3. Rotation of crops
4. Strip cropping
5. Dry farming
6. Construction of small basins along the contours to retain water which reduces velocity of water run off
7. Contour terracing
8. Gully control - construction of bunds, dams, etc.
9. Plantation along river banks.
10. Afforestation

Major Biomes of the World

- Biome has been defined as the largest recognizable sub-division of the terrestrial ecosystems, including the
total assemblage of plants and animal life interacting within the life layer (Biosphere).
- The average thickness of biosphere is 30 km. The upper limit of the biosphere is determined by the
availability of oxygen, moisture, temperature and air pressure.
- Each biome is usually named by its dominant vegetation
- The major terrestrial biomes are:
1. Equatorial or Tropical Rain Forest Biome.
2. Tropical Deciduous Forest and Shrub Biome.
3. Tropical Savanna Biome.
4. Temperate Rainforest Biome.
5. Mid-latitude Broadleaf and Mixed Forest Biome.
6. Desert Biome.
7. Mediterranean Biome.
8. Mid-latitude grassland Biome.
9. Cold Desert and Semi-desert Biome.
10. Taiga Biome
11. Tundra Biome.
- Important characteristics of the major terrestrial biomes are given below in tabular form:
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Social Forestry
- Social forestry has been defined differently by the different social scientists. In the opinion of some of
the experts, the trees planted by the community, individuals, government or the individuals outside the
conventional forest areas is known as social forestry.

- Social Forestry has also been defined as the forest by the people; of the people; and for the people.

Objectives

- The main objectives of social forestry are as under:

1. to meet the fuelwood and timber requirements of the fast growing rural population.

2. to provide fodder to livestock and cattle.

3. to provide raw materials for the cottage and household industries, e.g. basket making, bidi- making,
manufacturing of cane goods, sports goods, etc.

4. to obtain forest products like, gum, lac, wax, honey, resins, etc.

5. to generate rural employment for the landless workers and marginal farmers.

6. to work as a wind break.

7. to check soil erosion and flood control.

8. to keep the environment in a healthy condition and to improve the resilience characteristics of the
ecosystem.

9. to provide the places of recreation for the rural people.

Classification of Social Forestry

(i) Rural forestry developed on the community land.
(ii) Social forestry developed on culturable wastelands along the roads, railways, canals and river banks.
(iii) Forestry developed by the individual farmers along the field boundaries.
(iv) Urban forestry developed by the government, NGOs or community on the outskirts of the urban
areas.
(v) Forestry developed by the tribals in the degraded forest areas.
Problems and prospects
- In India, social forestry has great scope in the degraded tracts of the Himalayas, hills of North -East India.
Chhotanagpur Plateau, Vindhyan and Satpura Systems. Aravallis, Western Ghats, Eastern Ghats, and on
the culturable wastelands along the railway tracts, roads, canals and rivers.
- The survival rate is very poor and mass involvement is not at the desired level. Apart from the good
quality seedlings, fencing of the planted trees is a must to get better results. Extension services and co-
operation of the rural people by providing them incentives may go a long way in making social forestry
a big success in the country.
Notes

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Agro Forestry
- Agro forestry is a system of land use in which perennial trees are used as annual agricultural crops to
obtain more income. Apart from money, agro-forestry provides wood, timber and fodder to the cultivator.
Some of the farmers, devote their fields for the plantation of perennial trees, while to small farmers plant
trees along the borders of their holding. Agro forestry, however, lowers the underground water table and
depletes the natural fertility of the soil Agro-forestry has become quite popular in the Sutlej-Ganga Plain.
Various Forms of Agroforestry
• Agri-silviculture system: Concurrent production of agricultural corps & forest trees.
• Silvipastoral System: Forest based livestock production system where production of wood and rearing of
domestic animals are done simultaneously.
• Agro-silvipastoral system: Land is utilized simultaneously for the production of agricultural crops, forest
trees and rearing of domestic animals.
• Multipurpose forest tree production system: In this system trees are grown not only for wood but also
for leaves, fruits, fodder and other useful by-products, including soil cover crops and intercropping with
high value spices in man-made plantations.
Benefits of Agroforestry System
A) Environmental benefits
• Reduction of pressure on natural forests.
• More efficient recycling of nutrients by deep rooted trees on the site.
• Better protection of ecological systems.
• Reduction of surface run-off, nutrient leaching and soil erosion through impeding effect of tree roots and
stems on these processes.
• Improvement of microclimate, such as lowering of soil surface temperature and reduction of evaporation
of soil moisture through a combination of mulching and shading.
• Increment in soil nutrients through addition and decomposition of litter fall.
• Improvement of soil structure through the constant addition of organic matter from decomposed litter.
B) Economic benefits
• Increment in the output of food, fuel wood, fodder, fertilizer and timber;
• Reduction in incidences of total crop failure, which is common to single cropping or monoculture systems;
• Increase in levels of farm income due to improved and sustained productivity.
C) Social benefits
• Improvement in rural living standards from sustained employ­ment and higher income.
• Improvement in nutrition and health due to increased quality and diversity of food outputs.
• Stabilization and improvement of communities through elimination of the need to shift sites of farm
activities.
Notes

Physical Geography 17