This Power Point Presentation intends to explore the basic understanding of soil sciences in general and soil formation in particular.

1. PLANT ECOLOGY
Soil Importance; Origin; Formation; Composition;
Physical; Chemical and Biological components;
By
N. Sannigrahi, Associate Professor
Department of Botany
Nistarini College, Purulia (W.B) India

2. WHAT IS SOIL?
 Soil is the topmost part of the earth crusts treated as the
sustainable treasure of resources for the avenue of the
biological entities. Any part of the earth’s surface that supports
vegetation also bears a covering of soil. Soil is thus usually
defined as “any part of earth’s crust in which the plants root”.
Muddy bottoms of ponds, porous rock surfaces, ravine or
glacial deposits, bottoms of lakes, peats etc--, all are thus soils.
Soil is actually formed as a result of long term process of
complex interactions leading to the production of mineral
matrix in close association with interstitial organic matter-
living as well as dead. Modification of parent mineral matter
takes a fairly long time and such modification is actually the
result of interactions between climatic, topographic and
biological effects.

3. SOIL-RENEWABLE RESOURCE

4. IMPORTANCE OF SOIL
 “Soil is a natural body developed by natural forces acting on
natural materials. It is usually differentiated into horizons of
minerals and organic constituents of variable depths which
differ from the parent materials in morphology, physical
constitutions, chemical properties, composition and biological
characteristics”- Joffe and Marbut. According to R.F.
Daubenmire, “soil is the upper part of earth crust in which
plants are anchored.” He defines soil as weathered superficial
layer of earth crust with which are mingled living organisms
and products of their decay. According to Hilgard, 1917
(American school), “it is, more or less, loose, friable material
in which, by means of their roots, plants may or do find a
foothold, nourishment as well as other conditions of growth.”
 According to Raman, 1928 (German school), “soil is the upper
weathering layer (i.e., layer subjected to physical and chemical
changes) of the solid earth crust.”

5. SOIL & ECOSYSTEM
 Soil plays a vital role in the Earth’s ecosystem. Without soil
human life would be very difficult. Soil provides plants with
foothold for their roots and holds the necessary nutrients for
plants to grow; it filters the rainwater and regulates the
discharge of excess rainwater, preventing flooding; it is
capable of storing large amounts of organic carbon; it buffers
against pollutants, thus protecting groundwater quality; it
provides Man with some essential construction and
manufacturing materials, we build our houses with bricks
made from clay, we drink coffee from a cup that is essentially
backed soil (clay); it also presents a record of past
environmental conditions.
 Soil functions are general capabilities of soils that are
important for various agricultural, environmental, nature
protection, landscape architecture and urban applications. Six
key soil functions are:

6. ROLE OF SOIL
 Food and other biomass production
 Environmental Interaction: storage, filtering, and
transformation,
 Biological habitat and gene pool,
 Source of raw materials,
 Physical and cultural heritage,
 Platform for man-made structures: buildings, highways,
 It acts as one of the important renewable and replenish able
resources for the sustainable development,
 It is the treasure of the valuable biodiversity resources,
 Last but not least, it makes an avenue of the succession to
make the avenue of forest, the most important natural
ecosystem of the blue planet.

7. ORIGIN; FORMATION
 The whole process of soil formation is categorically divided
into two stages-
 Weathering which is the breaking down of bigger rocks into
fine , smaller mineral particles
 Pedogenesis -modification of mineral matter through
interaction between biological, topographic and climatic
effects which solely responsible into great potential soil types.
 The bare rock surfaces undergoes physical. Chemical and
biological processes that lead to the physical and chemical
disruption of their components The weathering processes are
physical as well as chemical
 A. PHYSICAL-
 A. Wetting-drying to disrupt the lattice materials

8. WEATHERING
 B. Heating & cooling to disrupt the heterogeneous crystalline
rocks through differential coefficients of thermal expansion
 Freezing to disrupt the porous, lamellar or vesicular rocks by
frost shatter due to expansion of water by freezing
 Glaciations in which larger masses of snow and ice glaciers
while falling may cause physical erosion of rocks,
 Solution which more mobile components of rocks such as
calcium , sulphates are simply removed by agents like water
 B. CHEMICAL
 Hydration in which the rocks swell as a result of taking water
 Hydrolysis in which hydrolysis of the different components
take place
 Oxidation-reduction to cause disruption of rocks

9. PEDOGENESIS
 Carbonation which leads to solution loss of limestone or
disruption of calcium carbonate cemented rocks as the
hydrogen carbonate is more soluble than carbonate,
 Chelation in which some chemicals exudates , produced
through biochemical activity of microorganisms are able to
dissolve out mineral components of the rocks. The metals
dissolved with organic products of microbial activity are
known as chelates.
 PEDOGENESIS
 Soil formation is the interaction of four factors-the parental
material, the climate, the age and the biological factors. The
combined actions of wind, water and air, the crusts of
weathered rock debris are converted into true soils consisting
of a complex mineral matrix in association with a variety of
organic compounds and rich microorganism population.

10. PEDOGENESIS
 During pedogenesis , there are various organic compounds,
dead organic matter, living organisms including plants to the
mineral matter. As a result of mineralization of dead organic
matter, the minerals are then gradually added to the different
layers of developing soil. This soil, when fully developed can
be seen having a number of layers-horizons of a soil, known as
soil-profile.
 In order to emphasize the part played by living plants and
animals in soil formation, the following equation can be
placed(Taylor, 1930)
 S=M(C+V+VA+A)t+ D where A=animals, C=climates,
D=deposition, M=parent material, t=time & V=vegetation. The
entire process is initiated and continued primarily by energy
from sun and secondly the potential energy bound up in
crystals, molecules and atoms.

11. PEDOGENESIS

12. COMPOSITION OF SOIL
 Soil having three –phase state of solid, liquid & gas have their
own physical, chemical proprieties in an equilibrium or
transient state. In addition to these, each soil has distinctive
flora and fauna of bacteria, fungi, algae, BGA, protozoa,
rotifers, nematodes, oligochaetes, mollusks, arthropods
etc.These organisms act as biotic components. The liquid and
gas phases are quite homogenous but the solid phase is
heterogeneous consisting of a range of different sized
inorganic particles of silica, silicate clay, metal oxides and
other components. These are all present in varying degree of
associations with different type of organic matter.
 Soil complex consists of –mineral matter, soil air, soil water,
soil solution, humus and soil organisms.

13. COMPOSITION OF SOIL
 MINERAL MATTER
 Due to varying degree of weathering of parent material-rock,
the mineral particles of different sizes. The clay(less than
0.0002mm), slit (0.002-0.02 mm), fine sand (0.02-.20 mm) etc
are present. On the basis of the particles size, soil textural
groups like sandy soil, Loamy soil, Loam soil, Slit are made
.The soil structure and porosity are varied depending upon the
different constituents present thereafter.
 SOILAIR
 There are spaces between mineral particles as well as between
aggregates of the soil. These spaces are occupied by different
gases and the size and number of such spaces differ in
different textural groups of soil. Sand have larger pore spaces
than fine textured soil. The different gases like oxygen, Carbon
dioxide varies depending wet soil or dry soil

14. COMPOSITION OF SOIL
 SOIL WATER
 The principal source of soil water is precipitation and the soil
water content is much related to texture of the soil. Some soils
like sandy are physically dry soil due to bigger pore size but
due to high degree of salinity, some soils are treated as
physiologically dry soil. Soil water mainly classified as
hygroscopic, capillary, gravitational or combined water along
with the water vapor remains present. All the water present in
the soil is not available by the plants. The total amount of
water present in the soil is called Holard.The available water
by the plants is called Chesard and the rest not available by the
plants are called Echard. Some terminologies like soil water
potential, field capacity, moisture equivalent, water holding
capacity, hygroscopic coefficient and permanent wilting
percentage etc are used to denote the water status of the soil.

15. SOIL SOLUTION-CHEMICALS
 There are two important chemical components-organic matter
and chemicals in solution. There exists a weak solution of
various salts hand it contains all k9st all the essential minerals.
Complex mixtures of minerals like carbonates, sulphates,
nitrates, chlorides and organic salts of Ca, Mg, Na, K etc are
found dissolved in water. The chemical nature of soil solution
depends on the nature of the parent matter and the climacteric
along with the other factors involved in pedogenesis. The salts
remain in ionic condition and the property of exchanging
cation is called cation Exchange capacity (CEC) of soils. Most
metallic elements which are taken by the plants are absorbed
as cations and they exist in three forms-poorly soluble
components of mineral or organic matter, absorbed into the
cation exchange complex and in small quantities in soil
solution. Soil with more or less optimal concentrations of
various nutrient solutes in them called eutrophic and whereas
those in suboptimal concentrations are called oligotrophic

16. SOIL SOLUTION-CHEMICALS
 Soil acidity is associated with the presence of Hydrogen and
aluminum ions on the exchange complex and the existence of
an equilibrium solution of hydrogen ions in their interstitial of
water of soil. It is expressed in terms of pH and the pH values
shows much correlation with soil type, vegetation type, profile
horizon. This affects the plant’s growth , lime requirement and
mineral nutrition. The pH values ranges from 3.0-8.4.alkali
soils with high sodium carbonate content while drained gleys
have 2.0-less.Plants are regarded as calcicoles having pH
tolerance up to 6.5 whereas calcifuges ranges below 3.8-
4.0.Soil pH strongly affects the microbial activities as below
5.0 pH , bacterial and fungal activities are reduced. Some soil
borne disease like root rot of cotton, tomato, potato etc may be
uncontrolled due to lowering pH. Some plants called
halophytes can tolerate high salt concentrations mostly found
in the mangrove areas. Salinity brings marked physiological
changes and to counter the salinity, vivipary and salt
respiration become common occurrence.

17. SOIL ORGANISMS
 The biological system of soil complex is comprising of diverse
type of living organisms as stated earlier and these organisms
play a pivotal role in maintenance of soil fertility through
nitrogen fixation and others responsible for return of essential
elements back to soil as a part of the decomposition activity.
Following are some of the microorganisms play a crucial role
in this regard.
 NITROGEN FIXATION- Bacteria like Azetobacter,
Clostridium & Rhizobioum and BGA like Nostoc, Anabena,
Tolypothrix, Oscillatoria etc fix atmospheric Nitrogen to
improve soil fertility.
 ROOT GROWTH- Some bacteria and fungi in the rhizosphere
zone of soil secrete growth hormones like IAA affecting the
growth of the microbes.
 ANTIBIOSIS-some microorganisms produce metabolic
products that cause killing of other microbes called antibiosis.

18. SOIL ORGANISMS
 SOIL BORNE DISEASE- Some fungi, bacteria and
nematodes etc are serious pathogens of root of plants. They
cause considerable loss of the quality and quantity of the yield.
 SOIL FORMATION- Some BGA and bacteria produce
mucilaginous substances which help in biding soil particles
into larger aggregates. Burrowing worms , as earthworms and
other animals besides helping in humus production, also
improves aeration of soil. This may have strong positive affect
on the existing vegetation.
 DECOMPOSITION OF ORGANIC MATTER- The
mineralization process is very important for soil formation as
well as the nutrients recycling .A variety of bacteria, fungi,
actinomycetes and soil animals play a very important role in
this regard.

19. SOIL ORGANIC MATTER
 Besides inorganic minerals, some organic residues derived
either from dead remains of plants and animals or through
metabolic activities of living organisms are present in the soil.
When the plants and animals die, their dead remains are acted
upon by a number of microorganisms and are finally degraded
or decomposed into simple organic compounds. A product of
this microbial decomposition is humus which is a dark
colored, jelly-like amorphous substance composed of residual
organic matters not readily decomposed by soil
microorganisms. The process of humus formation is called
humification. The chief elements found in humus are carbon,
hydrogen, oxygen, sulphur and nitrogen. The important
compounds found in it (humus) are carbohydrates, phosphoric
acid, some organic acids, fats, resins, urea, etc.

20. SOIL ORGANIC MATTER
 Tree litter (very little decomposed dead matter) also contains
some inorganic substances as lime, potash, Mn, Mg, silica, Cu,
Al, Ga, Na, K, etc. Humus is a dynamic product and is
constantly changing because of its oxidation, reduction and
hydrolysis. Hence, it has no definite chemical composition. It
has much carbon content and less nitrogen.
 Humus is not soluble in water. It is present in soil in the form
of organic colloids. The amounts of humus in different soils
vary greatly. Humus percentage in the soil is affected by
climatic and biological factors. It is less in arid soils and very
high in humid soils. In the top layer of the soil, humus quantity
is greater than in the deep layers.
 In temperate regions, the organic matter reflects the gross
difference between soil groups. Depending upon the nature of
parent matter, vegetation and climatic condition, there develop.

21. SOIL ORGANIC MATTER
 Different type of humus- Mor humus and Mull humus.
 MOR HUMUS-It is known as raw humus, a true podsol (type
of soil) having a range of pH below 3.8-4.0.Moderate rain
along with nutrient-deficient , well drained parent matter due
to podsolisation produce mor humus. Earthworms are absent.
The most prominent feature of podsol is the intensive elevation
of the surface horizons with mobilization of organic matter and
its redeposit ion at lower level. This fully developed podsol is
very acidic and its cation exchange complex is strongly
desaturated.Thus, organic matter in acidic conditions does not
decompose rapidly due to inhibition of microbial activities.
Organic matters deposits as peat or muck.
 MULL HUMUS- Mull is characteristic of brown forest soils
.Fine textured , nutrient rich rock with broad leaved forest
cover develop mull humus forms. It is microbiologically rich

22. SOIL ORGANIC MATTER
 than mor. It supports greater bacterial and fungal population .It
is associated with soil pH values above 5.0 and with the
abundance of divalent cations and well developed earthworm
fauna. As grey, brown grey or blackish material, it is diffusely
incorporated amongst the soil particles by biological mixing.
Since the microbial decomposition is rapid, no plant or
microbial remains are recognizable in mull. It is amorphous
and colloidal in nature
 .(a)It makes the soil fertile by the actions of soil enzymes.
 (b) It provides nutrients to the plants and microorganisms.
 (c)On complete decomposition, it forms several organic acids
which serve as solvents for soil materials. Thus humus
increases the availability of minerals in dissolved state to
plants.

23. SOIL ORGANIC MATTER
 (d) Because it is porous, it has got high capacity for retaining
water.
 (e) Humus makes the soil porous, thus increases the aeration
and percolation which make the soil more suitable for the plant
growth.
 (f) It also acts as weak cement thus binds the sand particles.
 (g) Presence of humus in the soil increases the rate of
absorption in plants.
 (h)It holds and slowly releases different minerals under the
action of the organisms as a part of renewable resources.
 (i) The oxidation-reduction potential and the buffering
capacity of the soil is maintained by humus.

24. THANKS FOR YOUE PLEASURE
 ACKNOWLEDGEMENT
 1.Google for images
 2.Different WebPages for content
 3.Ecology & environment-P.D.Sharma
 4.Ecology & Environmental Biology- T.K.saha
 5. A text book of Ecology- S.Chand & company.
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