Biological weathering,Biosphere-soil forming factor,Biological mediated soil forming process,Biotic factors influencing genesis of soil aggregation and soil structure

1. BIOTIC FACTORS IN SOIL FORMATION-AGGREGATION –SOIL STRUCTURE,
SOIL DEVELOPMENT
AGM 504- SOIL MICROBIOLOGY
B.KARTHIKEYAN
2019520103
SOIL SCIENCE& AGRL.CHEMISTRY
AC&RI MADURAI
TAMIL NADU AGRICULTURAL UNIVERSITY

2.  INTRODUCTION
 BIOLOGICAL WEATHERING-CAUSES
 SOIL FORMING FACTORS – BIOSPHERE
 BIOLOGICAL MEDIATED SOIL FORMING PROCESS
 STAGES OF SOIL DEVELOPMENT
 SOIL AGGREGATION
 FLOCCULATION AND DEFLOCCULATION
 BIOLOGICAL FACTORS IN GENESIS OF SOIL STRUCTURE
 REFERENCES
NUT SHELL

3. INTRODUCTION TO SOIL FORMATION

4. 1)WEATHERING
Physical disintegration and chemical decomposition of rocks
TYPES
 Physical weathering
 Chemical weathering
 Biological weathering

5. • Biological weathering is the effect of living organisms, such as plants and animals,
have on rocks and other inanimate objects
• When biological weathering occurs, the living organism breaks down the rocks
through either mechanical (Biophysical) or chemical weathering (Biochemical
weathering) or the use of both
There is strictly no biological weathering, they are aiding tool of physical and
chemical weathering - JENNY
Causes
 Man and Animals
 Higher Plants and Roots
 Micro- organisms
BIOLOGICAL WEATHERING

6. a)Higher Plants and Roots

7. a)Higher Plants and Roots
The roots of trees and other plants penetrates into the joints and crevices of the rocks.
As they grew, they exert a great disruptive force and the hard rock may break apart.
Roots can exert pressure up to 10.58 kg./sq. cm. when growing into a crack in rock.
(e.g.) pipal tree growing on walls/ rocks
 Plant roots conserve moisture and thus allowing moisture and air to enter in to the
rock for further action. (Biophysical weathering)
 The dead roots and plant residues decompose and produce carbon dioxide which is of
great importance in weathering.
 This carbon dioxide react with water and form carbonic acid which play major role in
carbonation (Biochemical weathering) .

8. b)Micro Organisms
 Microbial activity breaks down rocks&minerals by altering the rock’s chemical
composition, thus making it more susceptible to weathering.
 One example of microbial activity is lichen; lichen is fungi and algae, living together in
a symbiotic relationship. Fungi release chemicals that break down rocks&minerals;
the minerals thus released from rock are consumed by the algae.
 As this process continues, holes and gaps continue to develop on the rock, exposing
the rock further to physical and chemical weathering.

9.  Man cuts rocks to build dams, channels and construct roads and buildings. All
these activities result in increasing the surface area of the rocks for attack of
chemical agents and accelerate the process of rock decomposition.
 A large number of animals, birds, insects and worms, by their activities they make
holes in them and thus aids for weathering.
 In tropical and sub tropical regions, ants and termites build galleries and passages
and carry materials from lower to upper surface and excrete formic acids.The
oxygen and water with many dissolved substances, reach every part of the rock
through the cracks, holes and galleries, and thus brings about speedy
disintegration.
 Rabbits, by burrowing in to the ground, destroy soft rocks. Moles, ants and bodies
of the dead animals, provides substances which react with minerals and aid in
decaying process
c)Man and Animals

10.  The earthworms pass the soil through the alimentary canal and thus bring
about physical and chemical changes in soil material.
 Industrialisation can cause pollution such emission of sulphur dioxide which
can produce acid rain. Accelerate the chemical weathering process of hydrolysis,
carbonation and solution

11. 2)SOIL FORMING FACTORS

12. Effect of lichens, mosses and algae :
 Plants contribute to soil formation by helping to break down the rock.
 Lichens, mosses and algae grow on bare rocks and respire to produce carbon-
dioxide, that react with water to form carbonic acid, which dissolves primary minerals
and release the nutrients for plant growth.
 Algae uses atmospheric nitrogen, which is released in the soil upon the death of the
algae.
CO2+H2O H2CO3
CaCO3 + H2CO3 -» Ca(HCO3)2
Insoluble Soluble
4 KAlSi3O8 + 2H2CO3 + 2H2O 2K2CO3 + Si4Al4O10(OH)8+ 8SiO2
Orthoclase Kaolinite
It comprises all plant, man and microbiological life. These organisms improve soil
productivity by decomposing rocks, minerals and organic matter.
Plants
BIOSPHERE

13. Addition of organic matter (effect of grasses):
 Plants add organic matter to the soil. Grasses, litter and plant residues create a
surface layer of organic matter. Root density of grasses declines with depth. Many
roots die to produce a significant amount of organic matter.
 Grasses are very effective at offsetting leaching by recycling soluble materials.
Recycling occurs when ions are absorbed by roots and translocated up through the
plant. Recycling process is especially significant for cations such as Ca, Mg, Na, K
that are gradually leached from the soil.

14. Effect of forests:
 The horizon developed under forests is acid. The compounds of iron and aluminium
are more soluble and leach faster under acid conditions. The B-horizon of such soils
may therefore have illuvial deposits of organic matter and Fe and Al compounds in
addition to clay deposits.
Type of vegetation:
 Plants differ in their nutrient revival to soil. For example, the pines favor podzol
formation because of low bases and their leaches are acidic. Deciduous trees bring
up lime and produce brown earth.
Soil protection:
 Plants act as a vegetative cover and reduce normal erosion rates. Thus vegetation
acts as an agent of soil protection against the forces of disintegration.

15. Animals
Macroorganisms:
 Burrowing animals, earthworms, beetles, rodents, moles, centipedes, termites dig up
the soil, mix up the material and disturb the soil profile. They interrupt soil
development and tend to retard horizonation.
Earthworm:
 The organic and mineral matter is grinded and adds digestive juices. Their
excretions are rich in calcium and granular in structure.
 Crotovinas are abandoned pathways of rodents or earthworms filled with soil and
cover about 30% of the soil matrix. Wormiculture, i.e. the raising of earthworm on
the farmlands and the use of their casts as manure is being encouraged.
Man and soil formation
 Man is a destructive factor in soil formation – through exploitive land use,
converts the areas under natural vegetation to agricultural land which, with time and
under unprotective agriculture, get eroded

16. Micro-organisms: It includes microflora and microfauna.
Microflora: Bacteria, actinomycetes, fungi and algae
Microfauna: Protoza and nematodes
 Micro-organisms help soil development by slowly decomposing organic matter
and forming weak acids. Weak acids dissolve minerals faster than water.
 Soil supports billions of bacteria and other micro-organisms. Micro-organisms
like bacteria and fungi are responsible for processes like nitrification, sulfur
oxidation.
 They act on mineral content of rocks. These micro-organisms usually survive best
under aerobic conditions, and a temperature between 25°-30° C is optimum.
 These conditions are met in tropical and subtropical regions. Soil acidity (pH3.5
to 5.5) is favorable for fungi, and pH between 6.5 to 7.5 is best for bacteria.
Actinomycetes thrive well in slightly alkaline condition.

17. Profile characteristics of soils developed under different vegetation

18. Orders developed under different vegetation
Alfisol Mollisol Spodosol
Grasslands soil.
Thick, dark Ahorizon.
High % base saturation
coniferous soils.
Usually sandy.
Thick, bright white E horizon.
Sub-surface layer of accumulated
metal-humus complex (Bhs and Bs
horizons).
Forest soils.
Usually an A-E-B type
horizon development.
The A horizon is usually
less than 25 cm.

19. Fundamental Pedogenic Processes
a. Humification
b. Eluviation/Emigration
c. Illuviation /Immigration
Humification
 It is the process of transformation of raw organic matter into humus. When raw
organic materials are added in soil, their decomposition by various organisms
produces simple organic acids.
 Further bacterial polymerization of these organic acids produces a dark brown
colloidal substance resistant to microbial attack called humus.
MULL HUMUS developed under deciduous woodland, where base rich plants are
actively breakdown by soil biota
MOR HUMUS develops beneath coniferous woodland under cool wet climatic
condition. Breakdown slows due to absence of soil biota.
3)SOIL FORMING PROCESS

20. 1. Calcification
2. Decalcification
3. Podzolization
4. Laterization
Specific Pedogenic Processes
(a) Zonal Soil Forming Processes b)Intrazonal Soil Forming Processes
5. Gleization
6. Salinization
7. Alkalization
8. Pedoturbation
The soil forming processes that are
occurring under the prevailing
conditions of climate and biosphere
(active factors)
These pedogenic processes are more
influenced by certain local conditions such
as relief or parent material than climate
and vegetation

21. 1)PODSOLISATION
Climate: Cold–humid
Vegetation: Coniferous (acidic nature)
Parent material: Sandy (siliceous)
 It is a type of eluviation in which humus and sequioxides become mobile, leach out
from upper horizons and become deposited in the lower horizons.It requires high
content of organic matter and low alkali in the parent material. The process increases
the proportion of silica in A-horizons.
2) LATERISATION
Climate: Warm–humid
Vegetation: Broad leaf tropical vegetation (basic nature)
Parent material: Basic parent materials
(pyroxene, amphibole, biotite, chlorite).
 It is reverse process of podsolisation

22. 3)GLEIZATION
This process results in the development of a gley horizon (g) in
some part of profile due to poor drainage condition.
 Under such condition, iron compounds are reduced to
soluble ferrous forms. This is responsible for the production
of typical bluish to grayish horizons with mottling of yellow
and reddish brown colours.
Example for iron reducers
• Geobacter sp.,
• Rhodoferax ferrireducens,
• Geothrix fermentans,
• Ferribacterium limneticum,
• Geoglobus ahangari, and
• Shewanella sp.
 The term glei of Russian origin, which means blue, grey or green clay.

23. 4)PEDOTURBATION
It is the process of mixing of the soils. Mixing to some extent takes place in all soils.
Faunal pedoturbation : Mixing by animals such as ants, earthworms, moles,
rodents and man himself.
Floral pedoturbation : Mixing by plants, as in tree tipping that forms pits and
mounds.
Argillo pedoturbation : Mixing of materials in solum by churning process caused by
swell - shrink clays as is observed in deep black cotton soil.

24. STAGES OF SOIL DEVELOPMENT
Formation of 1 cm soil its nearly take 1000 years time period

25.  Aggregates is the naturally occurring, arrangement of soil particles into peds.
That result from pedogenic process.
 The grouping or arrangement of individual soil particles into a larger grouping. The soil
peds are a cluster or grouping of sand, silt, clay, organic material, biological slimes,
and fungal masses. Single particles when assembled appear as larger particles. These
are called aggregates
Peds aggregates
SOIL AGGREGATION

26. SOIL AGGREGATION
• The initial stage in the aggregation is the process of flocculation.
• Individual colloids typically exhibit a net negative charge which
results in an electrostatic repulsion.

27.  In the presence of natural or artificial binding agents clay particles become more strongly
cemented together forming stable soil aggregates.
These binding agents may be:
1)Inorganic – Fe & Al oxides, carbonates, amorphous gels and sols; or
2)Organic – polysaccharides, hemicellulose,and other natural or manufactured
organic polymers.
GLOMALIN produced by arbuscular mycorrhizal fungi (AMF) called as super glue of soil

28.  When individual tiny soil particles especially fine clay, aggregate
together into small clumps of floccules, the phenomenon is called
flocculation
 It aids in the formation of stable aggregates
 Separation of compound particles to individual components by
chemical or physical means is called deflocculation or dispersion
FLOCCULATION AND DEFLOCCULATION

29. By the reduction of the forces of electrostatic repulsion allows the particles
to come closer together.
+
Flocculation
MECHANISM OF AGGREGATION

30.  Soil organic matter consist of polysaccharides,hemicellulose as well as number
of other natural polymers which are poly electrolytic in nature and have multiple
charges.It also contaion fats,oils and waxes.
These materials are attached to clay surfaces by means of
1)cation bridge
Clay - _ +Ca+ _ -OOC-R-COO- _ +Ca+ _ -Clay
(carboxyl group)
2)Hydrogen bonding
Clay - _ +H-OOC-R-COO-H+ _ - Clay
(carboxyl group)
3)Vander walls forces
4)Anion exchange or ligand exchange mechanism
clay- + -HO-R-OH- Clay-R-Clay + OH-
(Alcoholic group)
That’s why organic matter acts as very good binding agent
Functional groups of humus

31. As this process continues, the flocs become larger and larger forming the
more refined structural units.

33.  Aggregation of soil particles can occur in different patterns, resulting in
different soil structures. The circulation of water in the soil varies
greatly according to structure, Therefore, it is important for you to know
about the structure of the soil
Arrangement of primary particles and their aggregates into certain definite pattern is
called as soil structure
SOIL STRUCTURE

34. Soil Structural Types Soil Structure Size/ Class
 Very Fine (Very
Thin)
 Fine (Thin)
 Medium
 Coarse (Thick)
 Very Coarse
(Very Thick)

35. By definition, the grade of structure is the degree of aggregation, expressing
the differential between cohesion* within aggregates and adhesion* between
aggregates.
As these properties vary with the moisture content of the soil, grade of structure
should be determined when the soil is neither unusually moist nor unusually dry.
There are four major grades of structure rated from 0 to 3 as follows:
Soil Structure Grade
 Structureless = 0
 Weak = 1
 Moderate = 2
 Strong = 3

36. BIOTIC FACTORS AFFECTING SOIL STRUCTURE
Organic matter:
 Organic matter improves the structure of a sandy soil as well as of a clay soil.
 In case of a sandy soil, the sticky and slimy material produced by the
decomposing organic matter and the associated microorganism cement the sand
particles together to form aggregates.
 In case of clayey soil, it modifies the properties of clay by reducing its
cohesiveness. This helps making clay more crumby
 Some of the decomposition products of organic matter and the associated
microbial tissue act as cementing agents. Thus it has a stabilizing effect.
 Organic matter helps in the granulation of clay.

37. Plants, Roots and Residues:
 Plant foliage protects soil aggregates against the disintegrating action of raindrops.
 Root hairs penetrate clods, thus breaking the soil clods into desirable aggregates.
 Root excretions, water sorption by roots and pressure exerted by root penetration are
conducive to formation of stable aggregates.
 Grasses and legumes can restore deteriorated soil structure.
Soil Organisms
 Decomposition of organic matter by micro-organisms produces humic acids,
polysaccharides that impart stability to aggregates. Thus soil micro-organisms are
indirectly helpful in formation of stable aggregates.
 Macro-organisms like rodents and earthworms help soil aggregation by burrowing,
turning and mixing the soil. Earthworm’s activity has a remarkable effect in the
formation of stable aggregates. They excrete surface casts and form burrows, which
promotes granulation.

38. Microbes:
 Algae, fungi, actinomycetes and fungi keep the soil particles together. Fungi and
actinomycetes exert mechanical binding by mycelia, Cementation by the products
of decomposition and materials synthesized by bacteria

39. REFERENCE
 INTRODUCTORY SOIL SCIENCE –D K DAS
 TEXT BOOK OF SOIL SCIENCE – R.K.MEHRA
 SOIL GENESIS AND CLASSIFICATION(ISSS) -s.k. singh and p. chandran
 SOIL PEDOLOGY – J.SEHGAL
 FACTORS OF SOIL FORMATION- HANS JENNY
 FACTORS OF SOIL FORMATION Biota - A H Jahren, Johns Hopkins University, USA
 FACTORS OF SOIL FORMATION/HUMAN IMPACTS -J Sandor, C L Burras, and M
Thompson, Iowa State University, Ames, IA, USA
 ABIOTIC AND BIOTIC FACTORS INFLUENCING THE EFFECT OF MICROPLASTIC
ON SOIL AGGREGATION
-Anika Lehmann 1,2,* , Katharina Fitschen 1 and Matthias C. Rillig 1,2
 SOIL BIOTA, ECOSYSTEM SERVICES AND LAND PRODUCTIVITY- Edmundo
Barrios , Colombia