Unit 1 INTRODUCTION AND SOIL PHYSICS.pptx

Soil Science and Engineering
S. Satheeshkumar
Assistant Professor
Department of agriculture engineering
Kongunadu college of engineering and technology

Syllabus
Unit – I Introduction and Soil Physics
Unit – II Soil Classification and Survey
Unit – III Phase relationship and Soil Compaction
Unit – IV Engineering properties of soil
Unit – V Bearing Capacity and Slope Stability

Unit – I Introduction and Soil Physics
Soil- definition- major components- Soil
forming minerals and processes – Soil profile –
Physical Properties –texture- density – porosity-
consistence – color- specific gravity – capillary and
non capillary – plasticity. Soil air –soil water –
Classification of soil water – Movement soil water
.Soil colloids- organic and inorganic matter- ion
exchange – pH –Plant nutrient availability.

Introduction Soil science
Definitions:
Soil refers to the loose surface of the earth as
identified from the original rocks and minerals from which
it is derived through weathering process.
According to “ Buckman and brady”
Soil may be defined as a “A dynamic natural body on the
surface of the earth in which plants grow components of
mineral and organic material and living forms.

There are two basic concept of soil
1) Pedology
• A study of orgin, classification ,description of soil
• A/tPedology solid is natural body
2)Edaphology
• A study of soil from the stand pont of hiher plants
• A/T edaphology soil isnatural habitat
Organic soil
• 20% organic matter is low clay content
• 30% in high clay content
Mineral soil
• < 20% organic matter

Soil physics
• Study of soil physical parameters
Soil Chemistry
• Chemical composition
Soil morphology
• Study of characteristics of soil

Major components of soil
• The major components of the Earth are water, air/gases,
minerals, organic and biological components, microorganisms
and gases.

 The abiotic component of the soil accounts for about 40-45% of
the soil volume followed by air and water that occupy 25% each
with 5% covered by living things.
 Soil consists of four major components

Soil forming Minerals
 Minerals are naturally occurring, homogeneous inorganic soild
substance having a definite chemical composition and characteristic
crystalline structure, color and hardness.
Primary minerals
• Minerals that are original components of rocks are called primary
minerals.
• eg: Feldspar, Mica
Secondary minerals
• Minerals that are formed from changes in primary minerals and
rocks are callled secondary minerals.
• eg: Clay minerals
Essential minerals
• The minerals that are chief constituents of rocks are called
essential minerlas.
• eg: Feldspars, pyroxenes micas.

Minerals arranged in the order of their crystallization
Primary minerals
Ferromagnesian minerals
Ortho or Ino silicates like
- Olivine
- Pyroxene
- Amphiboles
Phyllosilicates
- Biotite
- Muscovite

Non ferrous Magnesium
Tectosilicates
- Felds pars
- Anorthite
- Albite
- Orthoclase
- Quartz
Secondary Clay minerals
Minerls
others

Soil forming Processes
• The processes contributing to soil formation involve gain and
losses of materials to the profile, movement of matter from
one part of the profile to another and chemical
transformation within individual horizons.
The sequences of processes in the formation of soil

Two processes involved in the formation of soil are:
a) Formation of regolith by breaking down (weathering) of the
bed rock
b) The addition of organic matter through the decomposition of
plant and animal tissues, and reorganization of these
components by soil forming processes to form soil.
Weathering:
• A process of disintegration and decompostion of rocks and
minerals which are brought about byphysical agent and chemical
process leading to the formation of regolith.
Regolith:
 It is a layer of loose heterogeneous superficial material covering
solid rock. It includes dust, soil, broken rock and other related
materials

Types of weathering
I) Physical weathering or mechanical(Disintegration)
II) Chemical weathering(Decomposition)
III) Biological weathering( Disintegration+ Decomposition)
I. Physical Weathering:
The rocks are disintegrated and are broken down to comparatively
smaller places without producing any new substances
1. Physical condition of rocks
2. Action of Temperature
3. Action of water - i) Fragmentation and transport ii) Action of
freezing iii) Alternate wetting and drying iv) Action of glaclers
4.Action of wind
5. Atmospheric electrical phenomenon

II. Chemical Weathering
• Decomposition of rocks and minerals by various chemical
processes is called chemical weathering.
• It is the most important process for soil formation.
Chemical Processes of Weathering
a) Hydration
b) Hydrolysis
c) Solution
d) Carbonation
e) Oxidation
f) Reduction

a) Hydration:
• Chemical combination of water molecules with a particular
substances or minerals leading to a change in structure.
b) Hydrolysis:
• It is due to dissociation of H2O into H+ and OH - ions which
chemically combined with minerals and bring about change in
crystalline structure.
c)Solution:
• The soluble substance are removed by the continuous action of
water and the rock no longer remains solid and forms holes.

d) Carbonation:
• Carbon dioxide when dissolved in water forms carbonic acid
The carbonic acid attacks many rocks and minerals and
being them into solution . The carbonated water has an itching
up on some rocks.
e) Oxidation :
• The process of addition of oxygen to minerals.
f) Reduction:
• The process of removal of oxygen from minerals

III. Biological weathering
Unlike physical and chemical weathering the biological or
living agents are responsible for both decomposition and
disintegration of rocks and minerals.
 Man and animals
 Higher plants and roots
 Micro – organisms
Factors affecting weathering minerlas
1. Climate condition
2. Physical Characteristics
3. Chemical and structural characteristics

SOIL PROFILE
• The vertical section of the soil showing the various layers from
the surfaces to the unaffected parent material is known as a soil
profile.
• Horizons – Individual layer
• Solum –Horizons above the parent materials are collectively
refereed to as the solum

O- Horizons
• It is called as organic layer
• It is formed in the upper part of the soil dominated by
fresh or decomposed organic materials
• It contains more than 30% organic materials
• It is mostly available in forest areas.
• Oi- Orgnaic horizon of the original plant and animal
residues, only slightly decomposed.
• Oe – Organic horizon, residues intermediately
decomposed
• Oa- organic horizon,residue highly decomposed.

A - horizon
• Top most mineral horizon formed adjacent to the
surface and
darker in colour.
E – Horizon
• Horizon that has been significantly leached of clay,iron,
aluminum oxide which leaves a concenration of
resistant minerlas such as quartz.
• It is light colour
B- Horizon
• This is a subsurface horizon in which the eluviation (
washing out) of materials has taken place from above
or below.

C – Horizon
• It is the horizon of unconsolidated materials
• It is relatively less affected by weathering.
R – Horizon
• It is the layer of unconsolidated bed rock.
Transistion Horzon
• It is a layer between the master horizons (O,A,E,B
and C)

Physical Properties
• The physical properties of a soil greatly influence its
use and behavior towards plant growth
• The physical properties also influence the chemical and
biological behavior of soil
• The physical properties of a soil depend on the
amount, size shape, arrangement and mineral
composition of its particles.

Important physical properties of soils
1.Soil texture
2.Soil density
3.Soil porosity
4.Soil consistence
5.Soil colour
6. Soil specific gravity
7.Soil capillary and soil non capillary
8.Soil plasticity

Soil texture
Definition:
Soil texture refers to the relative proportion of particles or
it is the relative percentage by weight of the three soil separates
viz., sand, silt and clay or simply refers to the size of soil particles.
The soil separates are defined in terms of diameter in millimeters
of the particles.
Soil separaters
• Soil separaters are specific ranges of particle sizes.
• The smallest particles sizes are clay particles and are classified
as having diameters of less than 0.002mm.
• The ranges of diameters of the three separates are: sand (
mm), silt ( mm), and clay (<0.002 mm).

There are a number of system of naming soil separates.
a) The American system developed by USDA
b) The international system – WRB by IUSS
c) The English system or British system (BSI)
d) European system
USDA - United state department of Agriculture
WRB - World Reference Base for soil Resources
IUSS – International Union of Soil Science
BSI – British Standards Institution

Soil textural classes
On the basis soils are classified into various textual classes like
sands , clays, slits, loams etc.
Sands – Sand group includes all soils in which the sand make up
at least 70% and clay separates 15%
Silt - Slit group includes all soils in which the Slit make up 70%
80% and
clay separates 12%
Clay : It a soil must contain at 35% of the clay separates and in
most cases not less than 40%.
Loams: The loam group, which contains many subdivisions, is a
more complicated soil textural class, However exhibit
approximately equal properties of sand ,silt and clay.

• Soil Texture :Texture refers to the relative proportion of
sand,silt and clay in a soil. Soil containing equal amount of
sand, silt and clay is called “loam”.
• sand + clay +silt = Loam
• For ex. 15 % clay, 20% silt and 65% sand is called “sandy
loam”.
• Soil Texture: size (mm)
• Clay 5.0
• Silt 0.002- 0.02
• Sand fine 0.02-0.2
• Sand coarse 0.2-2.0
• Gravel fine 2.0-5.0
• Gravel coarse >5.0

Textural triangle
• The soil texture triangle gives names associated with various
combinations of sand, silt and clay.
• A coarse-textured or sandy soil is one comprised primarily of
sand-sized particles.
• A coarse-textured or sandy soil is one comprised primarily of
medium to coarse size sand particles.
• A fine-textured or clayey soil is one dominated by tiny clay
particles.
• Due to the strong physical properties of clay, a soil with only 20%
clay particles behaves as sticky, gummy clayey soil.
• The term loam refers to a soil with a combination of sand, silt,
and clay sized particles. For example, a soil with 30% clay, 50%
sand, and 20% silt is called a sandy clay loam. Below Figure Soil
Texture Triangle Source: USDA

Figure Soil Texture Triangle Source: USDA

Importance of soil texture
• The texture of a soil is important because it determines soil
characteristics that affect plant growth.
• Texture has good effect on mangement and productivity of soil.
• Sand facilitates drainage and aeration . It allows rapid
evaporation and percolation.
• Sandy soils are poor store house of plant nutrients.
• Leaching of applied nutrient is very high
• They have fine pores and are poor in drainage and aeration
• Loam and slit loam soils are highly desirable for cultivation
• They have a high water holding capacity and poor percolation
which usually result in water logging.

Soil density
• Ratio between mass of the soil and volume of soil
• Soil density is expressed in two types
• 1. particle density 2. bulk density
• 1. Particle Density: - The weight per unit volume of the solid
portion of soil is called particle density.
• Generally particle density of normal soils is 2.65 grams per
cubic centimeter. The particle density is higher if large amount
of heavy minerals such as magnetite; limonite and hematite
are present in the soil.
• With increase in organic matter of the soil the particle density
decreases. Particle density is also termed as true density

Particle Density: -
Table Particle density of different
Soilt extural classes Textural classes
Particle density ( g/ cm3)
Coarse sand 2.655
Fine sand 2.659
Silt 2.798
Clay 2.837

2.Bulk Density :
• The oven dry weight of a unit volume of soil inclusive of pore
spaces is called bulk density.
• The bulk density of a soil is always smaller than its particle
density.
• The bulk density of sandy soil is about 1.6 g / cm3
• Normal soil is 1 – 1.6g/cm3
• Organic matter – 0.5 g/cm3

Soil Porosity:
• Depending upon the size pore spaces fall into two categories.
• These are:
(1) Micro-pore spaces (capillary pore spaces)
<0.05 mm
(2) Macro-pore spaces (non-capillary pore spaces)
> 0.05 mm
Porosity void ratio (e)= Volume of void (or) pores/Volume of soil

Specific surface
• The area occupied per unit weight of soil. In smaller particle
surface area is big. In bigger particle surface area is small .
Specific graviy
Specific graviy = weight or mass of a given volume of a soil/
weight or mass of a given volume of a wter.
• At 270C is a specific gravity
• Specific gravity of water = 1
Methods to find specific gravity
1.Pycnometer
2.Density bottle
Typs of specific gravity
1.Apparent specific gravity
2.Absolutr specific gravity

Consistence
• Resistance of a soil at various moisture content to
mechanical stresses.
1.Cohesion
2.Adhesion
Cohesion
• It is an attraction between like molecule
Adhesion
• It is an attraction between unlike molecule

• Soil consistence is described at three moisture levels namely
Wet soil
Moist soil
Dry soil
Wet soil:
• Consistency is denoted by terms stickiness and plasticity
Plasticity
• Its capacity to be moulded and retained the shape even when
the stress is removed.
Moist soil:
• Moist soil with least coherence adhere very strongly and
resists crushing between the thumb and forefinger.
Dry soil :
In the absence of moisture, The degree ofesistance is elated to
the attraction of particles for each other.

• Absorption of electromagnetic wavelength and reflection
• Combination or adherence of two or more patches of colors in
soil is called motting .This due to the presence of iron,
manages and copper in soil in patches.
• Soil colour indicates soil feature.
Kinds of soil colour
1. Lithchromic –Red soil from red sand stone
2. Pedochromic – Red soil from granite rock.
Soil colour and Temperature
1.Dark colour soil absorb more heat
2. Light colour soil reflect most of heat
Soil colour

To measure soil –Munsell colour chart
• Munsell Charts are a standard tool used by
geologists, civil engineers, and soil scientists.
• The tabbed charts include 10R, 7.5R, 5R, 2.5YR,
5YR, 7.5YR, 10YR, 2.5Y, 5Y, and 10Y-5GY color
ranges. Charts for tropical and semitropical
soils, and for Australia and SE Asia are included.

Unit 1 INTRODUCTION AND SOIL PHYSICS.pptx

Soil colour:
• Soil colour gives an indication of the various processes going-on in
the soil as well as the type of minerals in thesoil.
For example the red colour in the soil is due to the
• abundance of iron oxide under oxidised conditions (well drainage)
in the soil;
• dark colour is generally due to the accumulation of highly decayed
organic matter;yellow colour is due to hydrated iron oxides and
hydroxide;
• black nodules are due to manganese oxides;
• mottling and gleying are associated with poor drainage and/or high
water table.
• Abundant pale yellow mottles coupled with very low pH
areindicative of possible acid sulphate soils.
• Colours of soil matrix and mottles are indicative of the
• water and drainage conditions in the soil and hence
• suitability of the soil for aquaculture.

Factor affecting soil clour
1.Parent material (Red, quartz,white)
2.Soil moisture (DarK)
3. Organic matter (Dark black colour)
4. Iron component (Red Colour)
5. Slica, lime and other salts
6.Mixture of organic matter and iron oxides
7. Alternate wetting and drying condition
8. Oxidation –reduction condition

Capillary and non capilllary
Capillary
• It is the ability of a liquid to flow in narrow spaces
without the assistance of, or even in opposition to,
external forces like gravity.
• Capillarity is the primary force that enables the soil to
retain water as well as to regulates its movement
Non- capillary
• It is the downward movement of water due to gravity
especially that occurs in soil with macropores.

Soil Air
• It is a continuation of the atmospheric air
• It is in constant motion from the soil pores into the
atmosphere and from the atmosphere into the pore
space.
Soil aeration
• The circulation of air in the soil and renewal of
component gases likeO2 & CO2
Composition of soil air
1. Nitrogen – 79.2 %
2. Oxygen – 20.9 %
3. Carbon dioxide – 0.35%

Methods to find the soil aeration
1. Oxygen reduction or diffusion rate
The rate at which oxygen in soil air replenished .ODR
decreases with soil depth.
2.Oxidation reduction potential
Oxidized soil
a) Ferric ions (Fe3+)
b) Manganic (Mn4+)
Reduction Soil
i) Ferrous ion (Fe2+)
ii) Sulphides (s2-)

Factors affecting the composition of soil air
1.Nature soil
2.Types of crop
3.Microbialactivity
4.Seasonal variations
5. Temperature
Aeration problems in fields
1.Moisture content is too high
2.Exchange of gases are slow
a)By mass flow
B)By Diffusion

Mass flow
• Moisture content in loss due to evaporation, absorption,
drainage and internal drainge etc.,
• Atmosphere air re-enters into soil pore space
Diffusion
• Gases(Like N2,O2 )move from Higher concentration to lower
concentration
Important of soil aeration
1. Soil reaction and properties
2. Oxidation and reduction of inorganic elements
3. Plant and root growth
4. Microorganism population and activity
5. Formation of toxic material
6. Water and nutrient absorption
7. Development of plant diseases

Soil temperature
• It is an Important factor(like air, water & nutrients) for plant
growth.
• It affects plants growth directly and also indirectly by
influencing moisture, aeration ,structure, microbial and
enzyme activities.
• Specific crops are adapted to specific soil temperatures.
Source of soil temperature
• Solar radiation
• Heat from microbial activity
• organic matter decomposition
• Respiration
• Internal heat from earth

• The rate of solar radiation reaching the earth’s
atmosphere is called as solar constant.
• It has a average value of 2 cal cm-2 min-1.
Factors affecting soil temperature
a) Environmental factors
• The heat transmission into soil depends on
• Angle on incident radiation
• Latitude
• Season
• Time of the day
• Steepness and direction of slope and altitude
• Insulation by air ,eater vapour clouds smog etc.,

b)Soil factors
1.Thermal capacity of soil
• The amount of energy required to increase the temperature by
one degree is called Heat capacity.
• It is expreseed per unit mass(calories per gram)
• It is called as Specific heat of water
• The Specific heat of water is 1.00 cal g-1
• The Specific heat of dry soil is 0.2 cal g-1
2.Heat of vapouriation
• The evaporation of water from soil requires a large amount of
energy, 540 kilocalories Kg-1
• Soil water utilizes the energy from solar radiation to evaporate
• The specific heat of wet soil is higher than dry soil because of
surface soil will be sometimes 1 to 60C lower than the –surface soil
temperature.

3.Thermal conductivity and diffusivity
• The movement of heat in soils, the heat is transmitted through
conduction
• Thermal conductivity of soil forming martials is 0.005 thermal
conductivity units.
4.Biological activity:
• More the biological activity more will be the soil temperature.
5.Radiation from soil:
• Radiation from low temperatures isin longer wavelenths have
little ability to penetrate water vapour,air and hence soil remains
warming during night hours.
6.Soil colour:
• The ratio between the incoming and outgoing radiation is called
albedo.
Albedo = Reflected energy/Incident energy

7.Soil structure, texture and moisture:
• Compact soils have higher thermal conductivity than loose soils
• Natural structures have high conductivity than disturbed soil
structures.
8.Soluble salts:
• Indirectly affects soil temperature by influencing the biological
activities, evaporation etc.
Effect of soil temperature on plant growth
1.Soil temperature required of plants
2. Availability of soil water and plant nutrient
optimum range temperature
• The temperature at which a plant at which thrives produces best
growth is known as optimum range temperature.

Growth range temperature
• The entire range of temperature under which plant
can grow including the optimum range is known as
growth range temperature.
Survival limits temperature
• The maximum and minimum temperatures beyond
which the plant will die are called survival limits
temperatures.
Soil temperatures management
• Use of organic and synthetic mulches
• Soil water management
• Tillage management

Methods of measuring soil temperatures
a) Mercury soil thermometer
b) Thermo couple and thermistor
c) Infrared thermo meters
d) Automatic continuous soil thermographs
• The international meteorological organisation recommends
standard depths to measure soil temperatures at
10,20,50,&1000 cm.

Soil water and its classification
Soil water
• Water contained in soil is called soil moisture
• The water is held within the soil pores
• Soil water is an important component of the soil which
influences soil organisms and plant growth.
• Soil water with dissolved salts is called soil solution.
Importance of soil water
• It is a carrier of food and nutrients
• It is essential for photosynthesis
• Helpful for chemical and biological activities
• Play a major role in microorganism metabolic activity
• It regulates soil temperature
• It is a principal constituent of the growing plant

Retention of water by soil
The water is retained in the soil by following ways
1.Cohesion and adhesion
2.Surface tension
3. Polarity or dipole character
Facture affecting soil water
1. Texture
2. Structure
3. Organic matter
4. Density of soil
5. Temperature
6. Salt content
7. Depth soil
8. Types of clay

Classification of soil water
I. Physical classification
II. Biological classification
I. Physical classification
a) Gravitational water
b) Capillary water
c) Hygroscopic water
a)Gravitational water
• It moves downwards by gravity
• It is excess of field capacity
• It affects texture and structure
b) Capillary water
• Water held between capillary pores

• Capillary water is retained on the soil
Factor affecting capillary water
• Surface tension
• Soil texture
• Soil structure
• Organic matter
c) Hygroscopic water
• The water that held tightly on the surface of colloidal
substances. It is a non-liquid state.
• Primarily in vapour form
• Some microorganism may utilize hygroscopic water
• This water cannot be separated from the soil unless it is
heated.

Factors affecting hygroscopic water
• Size of the soil particle
• Fine textured soil
II Biological Classification of soil water
• There is a relation between moisture rention and its utilization
by plants.
• Soil moisture can be divided into three parts
Available water: The water lies between wilting coefficient and
field capacity.
Unavailable water: This includes the whole of the hygroscopic
water plus a part of the capillary water below the wilting point.
Super available or superfluous water: The water beyond the field
capacity stage is said to be super available.

Movement of soil water
The soil water move under different ways
1. Saturated flow
2. Unsaturated flow
3. Water vapour movement
1.Saturated flow
This occurs when the soil pores are completely filled with water
• This water moves at water potentials larger than-33lPa
• This flow is caused by gravity ‘s pull
• It begins with Infiltration
• Movement of excess water flowing through the wetted soil is
termed percolation
• The rat at which soil absorbs rain wate.r or irrigation water

Vertical water flow
The vertical water flow rate through soil is given by Darcy’s law
The rater at which groundwater flows is equal to the product of the
hydraulic conductivity multiplied by the hydraulic gradient
V=K(G)
V=Groundwater velocity
K= hydraulic conductivity
G= Hydraulic gradient
2. Unsaturated
• It is flow water held with water potential slower than 1/3 bar.
• Water will move toward the region of lower potential
• The rate of flow is greater as the water potential gradient
increases and the size of water filled pores also increases.

Factors affecting the unsaturated flow
• Amount of moisture in the soil affects the unsturated flow
3.Water Vapour movement
Two types
a)Internal moment – Liquid to vapour within soil face
b) External moment – Water s lost to atmosphere by
diffusion
Factor affecting water vapour movement
• Soil regimes
• Thermal regimes
Entry of water into soil
Infiltration
• It refers to the downwards entry ormovement of water into
the soil surfaces

Factors affecting infiltration
• Clay minerals
• Soil texture
• Soil structure
• Moisture content
• Vegetative cover
• Topography
Percolation
The movement of water through a column of soil is called
percolation. It is important for two reasons
• This is the only source of recharge of ground water which can be
used through wells for irrigation
• Percolating waters carry plant nutrients down and often out of
reach of plants roots

Permeability
• The relative ease of movement of water within the soil, the
characteristics determine how fast air and water move through
the soil is known as permeability.
Drainage
• The frequency and duration of periods when the soil is free
from saturation with water
• It controls the soil cum water relationship and supply of
nutrients to the plants.
Drainage class
Very poorly drained
poorly drained
Imperfect
Moderately well
Well
Excessive

Hysterisis
The moisture content at different tensions during wetting if
soil varies from the moisture content at same tensions during
drying. This effect is called as hysteresis.
• This due to the presence of capillary and non capillary pores
• The moisture content is always low during sorption and high
during desorption
• Hysteresis exists in soil minerals as a consequence of shrinking
and swelling
• Shrinking and swelling affect pore size on a microbasis as well as
on the basis of overall bulk density.
• The most important factor affecting hysteresis is the entrapment
of air in the soil under rewetting condition.
• The clogs some pores and prevents effective contact between
others

Soil Colloids
• The soil colloids are most active portion of the soil and largely
determine the physical and chemical properties of a soil
• The clay fraction of the soil contain particles less than 0.002 mm
in size.
• Particles less than 0.001 mm size posses colloidal properties and
are known as soil colloids
• The organic colloids include highly decomposed organic matter
generally called humus.
General properties of soil colloids
1. Size
2. Surface area
3. Surface charges – i) Ionizable hydrogen ion II) Isomorphous
substitution

4.Adsorption of cations
5.Adsorption of water
6.Cohesion
7.Adheson
8. Swelling and shrinkage
9. Dispersion and flocculation
10.Non permeability
Types of soil colloids
There are four major of colloids present in soil
1. Layer silicate clays
2. Iron and aluminum oxide
3. Allophane and associated amorphous clays
4. Humus

1.Layer silicates
• It is important silicate clays known as phyllosilicates (phyllon –
leaf)
• Because of their leaf-like or plate like structure
• There are comprised two kind of horizontal sheets
• One dominated by silicon and other by aluminum or
magnesium.
layer silicate clay
1:1 type clay
Eg.Keolinite
2:1 type caly (Expanding)
Eg. Montorillonite (smectitic clay)

2:1 type clay (Non expanding)
Eg.mica ,illite
2:2 typeclay
Eg. chloide
2.Iron and aluminum oxide( sesquioxide clays)
• Sesquioxides ( metal oxides ) are mixtures of
aluminum hydroxide.
• Examples of iron and aluminum oxides common in
soils are gibbsite (Al2O3.3H2O) and geothite
(Fe2O3.H2O)

3.Allophane and associated amorphous clays
• These silicates clays are mixtures of silica and alumina
• Clay are common in soils forming from volcanic as ( e.g.
Allophane)
• It is soil acidity
4.Humus
• It is amorphous dark brown to black nearly in water but
mostly soluble in dilute alkali.
• It is an organic colloidal and consists of various chains and
loops of linked carbon atoms.
• The negative charge of humus are associated with partially
dissociated enolic ,carboxylic and phenolic groups
• These groups in turn are associated with central unit varying
size and complexity.

Soil organic matter
• Substances containing carbon are organic matter.
• Soil organic matter consists of decomposing plant and animal
residues
• It also includes substances of organic origin either leaving
ordead
Factor affecting organic matter
1. Climate
2. Natural vegetation
3. Texture –fine texture high organc production
4. Drainage –power water
5. Cropping and tillage
6. Crop rotation and plant residues
7. Organic content
i) moisture content

8. Plant residue
i) Cellulose, legnin, starch
ii) Sugar, fat protein hemicellulose
9.Dry matter
• Carbon ,oxygen, hydrogen, nitrogen, and some micro
nutrients
Water soluble minerals
• Ammonium and nitrate
Water insoluble minerals
• Protein, sulphur, peptides
Classification of organic matter
Based of decomposition
1.Rapidly decomposed
Starch, sugar

2.Less rapidly decomposed
3. Very slowly decomposed- fat ,legnin
4.Aerobic decomposition products
• Co2, Ammonium, nitrate, sulphate, water
Minerals – Ca, Mg,Fe, Cu,Zn
5.Anaerobic products
Metane, hydrogen sulphide, ethyl alcohol,propionic acid

Decomposition of soluble substances
i) Ammonification
ii) Nitrifiation
iii) Denitrification
The conversion of organic nitrogen into ammonia is called
ammonification.
Nitrification process

Denitrification process
1.Converson of nitrate into gaseous nitrogen
2.Decompostion of insoluble substances
i) Breakdown of protein
Conversion of protein into amino acid
ii) Breakdown of cellulose
iii) Breakdown of starch
Decomposition of ether soluble substances
Iv) Decomposition of lignin
Legnin to sulphate
Legnin to posphate
V) Breakdown of Hemicellulose

Mineralization
• Biological conversion of organic forms of carbon ,nitrogen ,
sulphur into inorganic minerals.
• Immobilization:The conveson of inporganic forms of C.N,P and
S by the soil organism into organic forms is called
immobilization.
Factor affecting decompostion
• Temperature
• Soil mosture
• Nutrients
• Soil pH<4.8 or>8.5 not suitable
• Soil texture increased decomposition
• Other factors like toxic level elements

Role of organic matter in plant growth
• It creates granular structure
• It increases the water holding capacity of
soil
• It can be used as a mulching material
• It is a reservoir of nutrient
• It is helpful in soil reclamation
• Store house of exchangeable ion

Ion Exchange
• The process by which ions are exchanged between solid and
liquid phase or between solid phase if in close contact with
each other is called ion exchange
• The common exchangeable cations are Ca2+,Mg2+,H+,K+. The
common are SO4
2-, Cl- & PO4
2-.
• Exchange of cation is called cation exchange and exchange of
anion is called anion exchange.
Mechanism of cation exchange
• Calcium is added to an acid soil the following reaction takes
place

• Similarly when H+ is added to the soil solution through the
decomposition of organic matter or through acidic martials
Ca2+ is replaced from the exchange complex by H+.
Cation exchange capacity (CEC)
• The sum total of the exchangeable cations that a soil can
adsorb is called as cation exchange capacity
• Itisalso defined as theamountofcationic speciesbound at pH
7.0.
• Some author consider pH 4.0 as the appropriate point.
• Unit is centi mole/Kg
Anion exchange process
OH >H2PO4>Sulphate>Nitrate>Chloride

Anion exchange capacity
• The capacity ofsoil to hold anion is called aniom exchnage
capacity
Microcell
• Cation heldonsmall particles of clay andorganicmatterisknown
as microcell
The sum of exchange cation that the soil can absorb
• Sand :Capacity 0-5
• Lumy soil :10-10.5
Acidoids (acid forming minerlas)
• Aluminium and hydrogen
basoids (base forming minerals)
• Ca,Mg,Na

Monovalent
• Lithium
• Sodium<potassium< Rubium<hydrogen
Divalent
• Mg<Ca<Ba
Mixtureof of monovalent & divalent
• Na<Potassium< Aluminium <Mg<Ca<Hydrogen

Factors influencing CEC
1. Soil Texture
2. Organic matter
3. Nature of clay
4. Soil reaction
Significance or important of ion exchange
1. Effect on soil fertility
2. Availability of applied nutrients
3. Effect of adsorbed cations
4. Toxic ions
5. Effect on soil pH
6. Correction of soil problems
7. Very helpful for soil reclamation process

Soil reaction (pH)
• The important characteristic of the soil solution is its reaction
• The soil reaction describes the degree of acidity or alkalinity
• The acidity or alkalinity is expressed in terms of concentration
of H ions or OH ions
• the pH are used to express the concentration of Hand OH ion
• The term pH was introduced by Sorenson (1909)
• pH = -Log [H+], based on dissociation of water where
• [H+]× [OH-]= 10-14
pH sale and range in soil pH
Acidity Alkalinity
Extreme
acidity
Very
strongly
acidic
strongly
acidic
Moderat
ely acidic
Slightly
acidic
Slightly
alkalinit
y
Moderat
ely
strongly Very
strongly
Ext
re
me

To measure soil pH – pH meter
• Soil water suspension ratio 1:25
• In order to avoid soluble salt problems and add potassium
chloride
Factor affecting soil pH
• Presence of H2 and aluminum ions
• Presence of base saturation (<80 %soil acidity ,80-905 neutral,
> 90% alkaline)
• Nature of clay & native vegetation
• Exchange of ions& hydrogen fertilizers
• Nature of soil collids & climate
• Parent material and Precipitation
• Decomposition of organic matter& soil depth

Plant Nutrients
Chemical elements that are essential for the proper
development and growth of plants are typically referred to as
plant nutrients
There are 14 essential plant nutrients
• The primary macronutrients: nitrogen, phosphorous,
potassium
• Secondary macronutrients: Calcium, sulfur, magnesium
• Micronutrients/trace minerals: boron, chlorine, manganese,
iron, zinc, copper, molybdenum, nickel
• Macro Nutrients are consumed in plant tissue from 0.2 % to
4% on a dry matter weight basis
• Micro Nutrients are consumed in plant tissue from 5 to 200
ppm or less than 0.02% dry weight.

Process
• Plants take up essential elements from through their
roots and from the air through leaf.
• Nutrient uptake in the soil is achieved by cation
exchange wherein root hairs pump hydrogen
ions(H+) in to the soil through proton pump.
• Hydrogen ion displae cation attached to negatively
charged soil particles . So cation uptake by the root
• In the leaves stomata open to take in carbon dioxide
and expel oxygen.

Function of nutrients
Soil supplies macro and micro nutrient
Macronutrients(Derived from
air and water)
Carbon
Hydrogen
Oxygen
Macronutrients(Primary)
Nitrogen
Phosphorous
Potassium
Macronutrients(secondary and
Tertiary)
S,C,Mg
Micro nutrients
Iron
Molybdenum
Boron
Copper
Manganese
Sodium
Essential of sodium
Zinc
Nickel
Chlorine
Cobalt
Aluminium
Silion
Photosynthesis

Availability of Nutrients
At low pH
• Al,Fe, Mn (Available)
• Ca,N2,Phosphate (Unavailable)
At high PH
• Na ,Phosphate .Fe ,Mn, ( Unavailable)
Nitrogen
• pH (6.5-7.5)
Phosphorous
• PH (6.5-7.5)
Potassium
• Not affected by soil pH
• Alkaline –Non exchangeable condition

Calcium and magnesium
• Unavailable in soil condition
• Alkaline is not > than8.5
Ferrous ,Aluminium Manganese
• Acid soil –High (availlable)
• pH > 7.5 unavilable
Sulphur
• Not affected soil conditions
Micronutrients
• Soil alkaline- Cu,Zn ((unavilable)
• Acid soil – molybdenum9unavilable)

Factors affecting nutrient availability
• Soil pH
• Organic matter
• Soil texture
• Climate
• Crop removal
Nutrient interactions
• Soil mobility
• Plant mobility
• High performance varieties
• Manure applications
• Light & Temperature

Symptoms of nutrients deficiencies
• Nitrogen – Leavs are small and light green
• Phosphourous – Darkgreen foliage
• Potassium – lower leaves may be mottled
• calcium- young leaves die
• Mg- Lower leaves are yellow between veins
• Sulphur- light green upper leaves
• Iron –new upper leaves turn yellow between vein
• Mn- new upper leaves have dead spots over surface
• Boron- Stems and petiols are britlle
• Nitrogen-Iight green leaf if excess darkgreen
• Ammonium toxicity – from ferticlizers reducedplant growth
• Phosphorous- plant growth will be slow if excess direct effect in
plant

• Potassium – older leaved edge will look burn called as scorch
• Calcium – roots and leaves turn brown
• Mg- Plant growth will be slow
• Sulphur- leaves light green to yellow
• Boron – Abnormal development of the growing point
• Chlorine – young leaves will be wilt
• Copper – plant growth will be slow
• Iron –young leaves will bleaching
• Mn- plants green wil be stunted
• Mo- Flower formation are restricted
• Zinc- Affected leaves

Chemical used for correcting nutrient deficiencies
• Nitrogen – green colour
• P- Hardly growth
• K- biochemical plants
• Ca- Activate enzymes
• Mg- Photosysthesis
• Crop nutrition and fertilizer requirement
• Supplied from soil and fertilizer sources of
• Macro and miro nutrients

Types of fertilizers
1.Nitrgen fertilizers
Urea
• Ammonium nitrate
• Ammonium sulphate urea
• Ammonium sulphate
• Anhydrous ammona
• Urea –ammonium nitate solution
2.Phosphate fertilizers
• Mono – ammonium phosphate
• Ammonium polyphosphate

3.Ntrogen Phosphate
4.Potash Fertilizers
5.Sulphur fertilizers
Nutrient availability and mobility
Precipitation – Dissolved substance form solid and drop
out of solution called precipitation
Distillation – the opposite process where by solidn go
into solution phase and become solutes.
Fixation: Elements or certain ions such as NH4 become
physically and chemically bound in a nonexchangeable.

Unit 1 INTRODUCTION AND SOIL PHYSICS.pptx

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Unit 1 INTRODUCTION AND SOIL PHYSICS.pptx