SOIL TEXTURE
SIZE OF THE PARTICLES
HOW THESE PARTICLES CAN BE SEPARATED
TEXTURAL GROUPS
TEXTURAL CLASSES OF SOILS
PROPERTIES
WHY DIFFERENT SOIL TEXTURES HAVE THE PROPERTIES THEY DO ?
ROLE OF SOIL TEXTURE
SOIL TEXTURE
SIZE OF THE PARTICLES
HOW THESE PARTICLES CAN BE SEPARATED
TEXTURAL GROUPS
TEXTURAL CLASSES OF SOILS
PROPERTIES
WHY DIFFERENT SOIL TEXTURES HAVE THE PROPERTIES THEY DO ?
ROLE OF SOIL TEXTURE
Soil formation or pedogenesis is the combined effect of human impact on the environment, physical, chemical and biological processes working on soil parent material.
The Formation of a particular type of soil depends upon the physico-chemical properties of the parent rock, intensity and duration of weathering, climatic and other parameters. This module highlights these aspects for a basic understanding.
In this presentation, you can found that, what is soil, Definition of soil science and all details, properties of soil. This Presentation made by Md Rubel Hossain.
Thanks..
http://www.agrislide.com/
www.leadmoneymedia.com
please follow me here :
https://www.behance.net/rubel570
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THIS SLIDES SHOWS ABOUT THE KNOWLEDGE ABOUT THE HOW SOIL AIR ARE TRANSMITTED FROM ENVIRONMENT TO SOIL AND ALSO TEMPERATURE CONDUCTION AND CONVECTION AND RADIATION.
The Physical Properties of the Soil
Inckuding,
1. Soil Texture
2. Soil Structure
3. Soil Color
4. Soil Density
5. Soil Porosity
6. Soil Consistence
7. Soil Temperature
Effects of Soil Organic Matter in the Soil, Benefits of soil organic matter, Amount of Soil organic matter, Maintenance or improvement of SOM, Factors affecting formation and decomposition of SOM
The soil profile is one of the most important concepts in soil science.
Soil profile is the term used for the vertical section of mature soil generally up to the depth of 2 meter or up to the parent material to show the different layers or horizons of soil for study of soil in its undisturbed state.
It is made up of a succession of horizontal layer or Horizons.
This presentation will give you knowledge regarding soil texture, soil structure and their impacts on soil water. In addition it will provide idea about bulk density, particle density, porosity and some other parameters. Appropriate formulas and questions for practice also have been attached with the presentation
Soil formation or pedogenesis is the combined effect of human impact on the environment, physical, chemical and biological processes working on soil parent material.
The Formation of a particular type of soil depends upon the physico-chemical properties of the parent rock, intensity and duration of weathering, climatic and other parameters. This module highlights these aspects for a basic understanding.
In this presentation, you can found that, what is soil, Definition of soil science and all details, properties of soil. This Presentation made by Md Rubel Hossain.
Thanks..
http://www.agrislide.com/
www.leadmoneymedia.com
please follow me here :
https://www.behance.net/rubel570
https://plus.google.com/u/0/+MdRubelHossain570
https://www.facebook.com/rubel570
THIS SLIDES SHOWS ABOUT THE KNOWLEDGE ABOUT THE HOW SOIL AIR ARE TRANSMITTED FROM ENVIRONMENT TO SOIL AND ALSO TEMPERATURE CONDUCTION AND CONVECTION AND RADIATION.
The Physical Properties of the Soil
Inckuding,
1. Soil Texture
2. Soil Structure
3. Soil Color
4. Soil Density
5. Soil Porosity
6. Soil Consistence
7. Soil Temperature
Effects of Soil Organic Matter in the Soil, Benefits of soil organic matter, Amount of Soil organic matter, Maintenance or improvement of SOM, Factors affecting formation and decomposition of SOM
The soil profile is one of the most important concepts in soil science.
Soil profile is the term used for the vertical section of mature soil generally up to the depth of 2 meter or up to the parent material to show the different layers or horizons of soil for study of soil in its undisturbed state.
It is made up of a succession of horizontal layer or Horizons.
This presentation will give you knowledge regarding soil texture, soil structure and their impacts on soil water. In addition it will provide idea about bulk density, particle density, porosity and some other parameters. Appropriate formulas and questions for practice also have been attached with the presentation
- Formation and evolution of soil.
- Characteristics and classification of soils.
- Regularity and environmental features of soil distribution on Earth.
- Location of the soil in the biosphere.
- Morphological signs of soil profile.
- Structure of soil profile.
- Granulometric composition.
- Soil composition: properties and modes.
- General physical properties of soil.
The design of Farm cart 0011 report 1 2020musadoto
This report describes the best designing of a 200cc FARM CART MACHINE which will be useful to the farm fields due to the fact that, the purchase, repair and maintenance are affordable to all level of income earners. Despite the cost effectiveness of the machine, the report also tries to justify that the machine can be used multipurposely as it serves the purposes of been used as farm transport, mowering machine, boom spraying and or mini planter with two rows. All these can be achieved as long as the implements are attached with respect to the power capacity of the farm cart.
The report tells only the design and testing of machine excluding its farm implements design. Some best reviews from other study projects done by other people in the world provided a good reference for designing and implementation of this project. The project is initially costly because it needs to develop a prototype and test the different first ideas.
The project report describes the important of choosing to use the designed farm cart machine compared to other farm machines at the market which are most efficiently to be used by farmers in their fields.
The challenges are inevitable in any project, here in designing of this 200cc farm machine, the major issue is the funding because the fund for this project is from the pocket which is always insufficient as it depends to the meals and accommodation money distribution sponsored from the HIGH EDUCATION STUDENTS LOAN BOARD (HESLB) thus it takes longer to accomplish the project by waiting another quarter of the semester to continue with the project which affects the other part of normal life(in terms of meals and accommodation).
The report recommends that, the department of engineering sciences and technology and Sokoine University of Agriculture as a whole should invest into this technology by utilizing fully the idea and funding the project for more better improvement so as to attain the desired standard that can with stand the different farm field factors. These when taken into consideration there is a possibility to achieve the industrialization policy in our country and thereafter it is a better approach to modern agriculture.
CONSTRUCTION [soil treatment, foundation backfill, Damp Proof Membrane[DPM] a...musadoto
With reference to a construction site visited recently, describe in details key features
that can be observed on site as follows
Foundations backfilling, hardcore, soil treatment, DPM and BRC works prior
to pouring oversite concrete
CONSTRUCTION [soil treatment, foundation backfill, Damp Proof Membrane[DPM] and BRC for engineers (civil)
BASICS OF COMPUTER PROGRAMMING-TAKE HOME ASSIGNMENT 2018musadoto
Self- Check 1
Which of the following are Pascal reserved words, standard identifiers, valid identifiers, invalid identifiers?
end ReadLn Bill
program Sues‟s Rate
Start begin const
Y=Z Prog#2 &Up
First Name „MaxScores‟ A*B
CostaMesa,CA Barnes&Noble CONST
XYZ123 ThisIsALongOne 123XYZANSWER
ANSWERS
Paschal reserved words:
begin, end, program, Start, CONST, const
Standard identifiers:
ReadLn, „MaxScores‟, Bill, Rate
Valid identifiers:
XYZ123, ThisIsALongOne, A*B, Y=Z, CostaMesa, CA, First Name
Invalid identifiers:
123XYZ, Sues‟s, &UpFirstName, Barnes&Noble, Prog#2
Self- Check 2
Which of the following literal values are legal and what are their types? Which are illegal and why?
15 „XYZ‟ „*‟
$25.123 15; -999
.123 „x‟ “X”
„9‟ „-5‟ True
ANSWER:
The following values are legal and their type
Legal
Type
Illegal
15
Integer literal
$25.123
„XYZ‟
String Literal
.123
„X‟
Character Literal
„9‟
True
Boolean Literal
15;
-999
Integer Literal
-„5‟
Operator literal
„*‟
TP- Lecture 4.2
Self- Checked 1
Which of the following are valid program headings? Which are invalid and why?
(i) Program program; - INVALID using reserved ID
(ii) program 2ndCourseInCS; -INVALID because starts with digit
(iii) program PascalIsFun;- VALID program heading
(iv) program Rainy Day; -INVALID – contains space
Self- Checked 2
Rewrite the following code so that it has no syntax errors and follows the writing conventions we adopted
(i) Program SMALL;
VAR X, Y, Z : real;
BEGIN
Y := 15.0;
Z := -Y + 3.5;
X :=Y + z;
writeln (x, Y, z);
END.
ANSWER:
Program
ENGINEERING SYSTEM DYNAMICS-TAKE HOME ASSIGNMENT 2018musadoto
1. Read Chapter 4 – System Dynamics for Mechanical Engineers by Matthew Davies and Tony L. Schmitz and implement Examples 4.1 to 4.12 in Matlab.
2. Read Chapter 7 – System Dynamics for Mechanical Engineers by Matthew Davies and Tony L. Schmitz and implement Examples 7.1 to 7.11 in Matlab.
3. Read Chapter 9 – System Dynamics for Mechanical Engineers by Matthew Davies and Tony L. Schmitz and implement Examples 9.1 to 9.6 in Matlab.
4. Read Chapter 11 – System Dynamics for Mechanical Engineers by Matthew Davies and Tony L. Schmitz and implement Examples 11.1 to 11.7 in Matlab.
5. Read Chapter 2 - System Dynamics for Engineering Students: Concepts and Applications by Nicolae Lobontiu and attempt problem 2.18 (page 63).
6. Read Chapter 3 - System Dynamics for Engineering Students: Concepts and Applications by Nicolae Lobontiu and attempt problem 3.13 (pp 98 - 100).
7. Read Chapter 4 - System Dynamics for Engineering Students: Concepts and Applications by Nicolae Lobontiu and attempt problem 4.20 (page 146).
8. Read Chapter 5 - System Dynamics for Engineering Students: Concepts and Applications by Nicolae Lobontiu and attempt problems 5.15 (page 198), 5.21 (pp 199 - 200) and 5.27 (pp 201 – 202).
Hardeninig of steel (Jominy test)-CoET- udsmmusadoto
Controlling a material’s properties during processing is pivotal for any engineering field. A specific hardness for a metal is often a desirable characteristic for many applications, so controlling hardness is important during processing. To increase the hardness of steel, it is often quenched from a high temperature to form martensite, a hard yet brittle phase of iron. The extent of martensite formation, including hardness and depth of formation, is known as hardenability. This practical provides an experiment for measurement of hardenability in plain carbon steel and an alloyed steel according to, the Jominy End-Quench Test , (ASTM A255 – 10). The demonstration exercise involve quenching one end of a heated steel sample ,comparing and evaluating the hardness distribution using measurements obtained at different locations(distance interval) on the sample(specimens) surface.
1.1 The aim of the experiment
The aim of the experiment is to test the usefulness of the ultrasonic waves, by passing them through different
solids one can find out a lot of physical properties like young’s modulus , defects, Poisson ratio, Velocity of
sound in respective material this is due to the response of the received ultrasonic waves.
1.2 Theory of experiment
Ultrasonic testing (UT) is a family of non-destructive testing (NDT) techniques based on the propagation of ultrasonic waves in the object or material tested. In most common UT applications, very short ultrasonic pulse-waves with center frequencies ranging from 0.1-15 MHz, and occasionally up to 50 MHz, are transmitted into materials to detect internal flaws or to characterize materials. A common example is ultrasonic thickness measurement, which tests the thickness of the test object, for example, to monitor pipework corrosion.
Ultrasonic testing is often performed on steel and other metals and alloys, though it can also be used on concrete, wood and composites, albeit with less resolution. It is used in many industries including steel and aluminium construction, metallurgy, manufacturing, aerospace, automotive and other transportation sectors.
Ae 219 - BASICS OF PASCHAL PROGRAMMING-2017 test manual solutionmusadoto
Whether the Pascal program is small or large, it must have a specific structure. This
program consists mainly of one statement (WRITELN) which does the actual work
here, as it displays whatever comes between the parentheses. The statement is
included inside a frame starting with the keyword BEGIN and ending with the keyword
END. This is called the program main body (or the program block) and usually
contains the main logic of data processing.
1. The background of Fluid Mechanics
2. Fields of Fluid mechanics
3. Introduction and Basic concepts
4. Properties of Fluids
5. Pressure and fluid statics
6. Hydrodynamics
Fluid mechanics (a letter to a friend) part 1 ...musadoto
1. The background of Fluid Mechanics
2. Fields of Fluid mechanics
3. Introduction and Basic concepts
4. Properties of Fluids
5. Pressure and fluid statics
6. Hydrodynamics
Fluids mechanics (a letter to a friend) part 1 ...musadoto
1. The background of Fluid Mechanics
2. Fields of Fluid mechanics
3. Introduction and Basic concepts
4. Properties of Fluids
5. Pressure and fluid statics
6. Hydrodynamics
Fresh concrete -building materials for engineersmusadoto
CONCRETE
is a building Material made from a mixture of gravel ,sand ,cement,water and air ,forming a stone like mass on hardenning.
FRESH CONCRETE
It is a concrete that has not reached the final setting time.
Course Contents:
Introduction; Linear measurements; Analysis and adjustment of measurements, Survey methods: coordinate systems, bearings, horizontal control, traversing, triangulation, detail surveying; Orientation and position; Areas and volumes; Setting out; Curve ranging; Global Positioning system (GPS); Photogrammetry.
Fresh concrete -building materials for engineersmusadoto
General introduction
CONCRETE
is a building Material made from a mixture of gravel ,sand ,cement,water and air ,forming a stone like mass on hardenning.
FRESH CONCRETE
It is a concrete that has not reached the final setting time.
DIESEL ENGINE POWER REPORT -AE 215 -SOURCES OF FARM POWERmusadoto
The diesel engine (also known as a compression-ignition or CI engine), named after Rudolf Diesel, is an internal combustion engine in which ignition of the fuel which is injected into the combustion chamber is caused by the elevated temperature of the air in the cylinder due to mechanical compression (adiabatic compression). Diesel engines work by compressing only the air. This increases the air temperature inside the cylinder to such a high degree that atomised diesel fuel that is injected into the combustion chamber ignites spontaneously. This contrasts with spark-ignition engines such as a petrol engine (gasoline engine) or gas engine (using a gaseous fuel as opposed to petrol), which use a spark plug to ignite an air-fuel mixture. In diesel engines, glow plugs (combustion chamber pre-warmers) may be used to aid starting in cold weather, or when the engine uses a lower compression-ratio, or both. The original diesel engine operates on the "constant pressure" cycle of gradual combustion and produces no audible knock.
A diesel engine built by MAN AG in 1906
Detroit Diesel timing
Fairbanks Morse model 32
The diesel engine has the highest thermal efficiency (engine efficiency) of any practical internal or external combustion engine due to its very high expansion ratio and inherent lean burn which enables heat dissipation by the excess air. A small efficiency loss is also avoided compared to two-stroke non-direct-injection gasoline engines since unburned fuel is not present at valve overlap and therefore no fuel goes directly from the intake/injection to the exhaust. Low-speed diesel engines (as used in ships and other applications where overall engine weight is relatively unimportant) can have a thermal efficiency that exceeds 50%.[1][2
Farm and human power REPORT - AE 215-SOURCES OF FARM POWER musadoto
Farm is an area of land and its building, used for growing crops a rearing of animals or an area of land
that is devoted primarily of agricultural process with the primary objective of producing food and other
commercial crops. Or an area of water that is devoted primarily to agricultural process in order to
produce and manage such commodities as fibers, grains, livestock or fuel.
The process of working the ground, planting seeds and growing of planting known as farming.it can
described s raising of animals for milk and meat as farming.
ENGINE POWER PETROL REPORT-AE 215-SOURCES OF FARM POWERmusadoto
What is an Engine?
Before knowing about how the Petrol Engine works, let's first understand what an engine is. This is common for both petrol and diesel engines alike. An engine is a power generating machine which converts potential energy of the fuel into heat energy and then into motion. It produces power and also runs on its own power.
The engine generates its power by burning the fuel in a self-regulated and controlled „Combustion‟ process. The combustion process involves many sub-processes which burn the fuel efficiently and results in the smooth running of the engine.
These processes include:
The suction of air (also known as breathing or aspiration).
Mixing of the fuel with air after breaking the liquid fuel into highly atomized / mist form.
Igniting the air-fuel mixture with a spark (petrol engine).
Burning of highly atomized fuel particles which results in releasing / ejection of heat energy.
How does an Engine work?
The engine converts Heat Energy into Kinetic Energy in the form of „Reciprocating Motion‟. The expansion of heated gases and their forces act on the engine pistons. The gases push the pistons downwards which results in reciprocating motion of pistons.
This motion of the piston enables the crank-shaft to rotate. Thus, it finally converts the reciprocating motion into the 'Rotary motion' and passes on to wheels.
A petrol engine (known as a gasoline engine in American English) is an internal combustion engine with spark-ignition, designed to run on petrol (gasoline) and similar volatile fuels.
In most petrol engines, the fuel and air are usually mixed after compression (although some modern petrol engines now use cylinder-direct petrol injection). The pre-mixing was formerly done in a carburetor, but now it is done by electronically controlled fuel injection, except in small engines where the cost/complication of electronics does not justify the added engine efficiency. The process differs from a diesel engine in the method of mixing the fuel and air, and in using spark plugs to initiate the combustion process. In a diesel engine, only air is compressed
TRACTOR POWER REPORT -AE 215 SOURCES OF FARM POWER 2018musadoto
A tractor is an engineering vehicle specifically designed to deliver a high tractive effort (or torque) at slow speeds, for the purposes of hauling a trailer or machinery used in agriculture or construction. Most commonly, the term is used to describe a farm vehicle that provides the power and traction to mechanize agricultural tasks, especially (and originally) tillage, but nowadays a great variety of tasks. Agricultural implements 0may be towed behind or mounted on the tractor, and the tractor may also provide a source of power if the implement is mechanised.
The word Tractor is derived prior to 1900, the Machine were known as traction motor (pulling-machine).After the year 1900 both the words are joined by taking ‘Tract’ from Traction and ‘Tor” from motor calling it a Tractor.
In our Country tractors were started manufacturing in real sense after independence and at present we are self-sufficient in meeting demand of country’s requirement for tractors. Our country is basically an agricultural country where 75% of our population is directly or indirectly connected with agriculture. This cannot be produced with our conventional bullock pulled agricultural implements. Tractor is one of the basic agricultural machines
used for speeding up agriculture production.
WIND ENERGY REPORT AE 215- 2018 SOURCES OF FARM POWERmusadoto
Wind is the flow of gases on large scale. On the surface of the earth, wind consists of the bulk movement of air. In outer space, solar wind is the movement of gases and charged particles from the sun though space, while planetary wind is the outgassing of light chemical from a planet’s atmosphere into space. Wind by their spatial scale, their speed, the type of force that cause them, the region in which they occur and their effect. The strongest observed winds on planet in solar system occur on Neptune and Saturn. Winds have various aspects, an important one being its velocity, density of the gas involved and energy content of the wind.
Wind is almost entirely caused by the effects of the sun which, each hour, delivers 175 million watts of energy to the earth. This energy heats the planet’s surface, most intensively at the equator, which causes air to rise. This rising air creates an area of low pressure at the surface into which cooler air is sucked, and it is this flow of air that we know as “wind”. In reality atmospheric circulation is much more complicated and, after rising at the equator air travels pole wards. As it travels the air cools and eventually descends to the earth’s surface at about 30° latitude (north and south), from where it returns once again to the equator (a closed loop known as a Hadley Cell). Similar cells exist between 30° and 60° latitude (the Ferrell Cells) and between 60° latitude and each of the poles (the Polar Cells). Within these cells, the flow of air is further impacted by the rotation of the earth or the "Coriolis Effect". This effect creates a sideways force which causes air to circulate anticlockwise around areas of low pressure in the northern hemisphere and clockwise in the southern hemisphere
In summary, the origin of winds may be traced basically to uneven heating of the earth’s surface due to sun. This may lead to circulation of widespread winds on a global basis, producing planetary winds or may have a limited influence in a smaller area to cause local winds.
Introduction to AI for Nonprofits with Tapp NetworkTechSoup
Dive into the world of AI! Experts Jon Hill and Tareq Monaur will guide you through AI's role in enhancing nonprofit websites and basic marketing strategies, making it easy to understand and apply.
Safalta Digital marketing institute in Noida, provide complete applications that encompass a huge range of virtual advertising and marketing additives, which includes search engine optimization, virtual communication advertising, pay-per-click on marketing, content material advertising, internet analytics, and greater. These university courses are designed for students who possess a comprehensive understanding of virtual marketing strategies and attributes.Safalta Digital Marketing Institute in Noida is a first choice for young individuals or students who are looking to start their careers in the field of digital advertising. The institute gives specialized courses designed and certification.
for beginners, providing thorough training in areas such as SEO, digital communication marketing, and PPC training in Noida. After finishing the program, students receive the certifications recognised by top different universitie, setting a strong foundation for a successful career in digital marketing.
Synthetic Fiber Construction in lab .pptxPavel ( NSTU)
Synthetic fiber production is a fascinating and complex field that blends chemistry, engineering, and environmental science. By understanding these aspects, students can gain a comprehensive view of synthetic fiber production, its impact on society and the environment, and the potential for future innovations. Synthetic fibers play a crucial role in modern society, impacting various aspects of daily life, industry, and the environment. ynthetic fibers are integral to modern life, offering a range of benefits from cost-effectiveness and versatility to innovative applications and performance characteristics. While they pose environmental challenges, ongoing research and development aim to create more sustainable and eco-friendly alternatives. Understanding the importance of synthetic fibers helps in appreciating their role in the economy, industry, and daily life, while also emphasizing the need for sustainable practices and innovation.
June 3, 2024 Anti-Semitism Letter Sent to MIT President Kornbluth and MIT Cor...Levi Shapiro
Letter from the Congress of the United States regarding Anti-Semitism sent June 3rd to MIT President Sally Kornbluth, MIT Corp Chair, Mark Gorenberg
Dear Dr. Kornbluth and Mr. Gorenberg,
The US House of Representatives is deeply concerned by ongoing and pervasive acts of antisemitic
harassment and intimidation at the Massachusetts Institute of Technology (MIT). Failing to act decisively to ensure a safe learning environment for all students would be a grave dereliction of your responsibilities as President of MIT and Chair of the MIT Corporation.
This Congress will not stand idly by and allow an environment hostile to Jewish students to persist. The House believes that your institution is in violation of Title VI of the Civil Rights Act, and the inability or
unwillingness to rectify this violation through action requires accountability.
Postsecondary education is a unique opportunity for students to learn and have their ideas and beliefs challenged. However, universities receiving hundreds of millions of federal funds annually have denied
students that opportunity and have been hijacked to become venues for the promotion of terrorism, antisemitic harassment and intimidation, unlawful encampments, and in some cases, assaults and riots.
The House of Representatives will not countenance the use of federal funds to indoctrinate students into hateful, antisemitic, anti-American supporters of terrorism. Investigations into campus antisemitism by the Committee on Education and the Workforce and the Committee on Ways and Means have been expanded into a Congress-wide probe across all relevant jurisdictions to address this national crisis. The undersigned Committees will conduct oversight into the use of federal funds at MIT and its learning environment under authorities granted to each Committee.
• The Committee on Education and the Workforce has been investigating your institution since December 7, 2023. The Committee has broad jurisdiction over postsecondary education, including its compliance with Title VI of the Civil Rights Act, campus safety concerns over disruptions to the learning environment, and the awarding of federal student aid under the Higher Education Act.
• The Committee on Oversight and Accountability is investigating the sources of funding and other support flowing to groups espousing pro-Hamas propaganda and engaged in antisemitic harassment and intimidation of students. The Committee on Oversight and Accountability is the principal oversight committee of the US House of Representatives and has broad authority to investigate “any matter” at “any time” under House Rule X.
• The Committee on Ways and Means has been investigating several universities since November 15, 2023, when the Committee held a hearing entitled From Ivory Towers to Dark Corners: Investigating the Nexus Between Antisemitism, Tax-Exempt Universities, and Terror Financing. The Committee followed the hearing with letters to those institutions on January 10, 202
Executive Directors Chat Leveraging AI for Diversity, Equity, and InclusionTechSoup
Let’s explore the intersection of technology and equity in the final session of our DEI series. Discover how AI tools, like ChatGPT, can be used to support and enhance your nonprofit's DEI initiatives. Participants will gain insights into practical AI applications and get tips for leveraging technology to advance their DEI goals.
A workshop hosted by the South African Journal of Science aimed at postgraduate students and early career researchers with little or no experience in writing and publishing journal articles.
Operation “Blue Star” is the only event in the history of Independent India where the state went into war with its own people. Even after about 40 years it is not clear if it was culmination of states anger over people of the region, a political game of power or start of dictatorial chapter in the democratic setup.
The people of Punjab felt alienated from main stream due to denial of their just demands during a long democratic struggle since independence. As it happen all over the word, it led to militant struggle with great loss of lives of military, police and civilian personnel. Killing of Indira Gandhi and massacre of innocent Sikhs in Delhi and other India cities was also associated with this movement.
Model Attribute Check Company Auto PropertyCeline George
In Odoo, the multi-company feature allows you to manage multiple companies within a single Odoo database instance. Each company can have its own configurations while still sharing common resources such as products, customers, and suppliers.
2. SOIL TEXTURE
• Refers to feel, coarseness or
fineness of soil
• -Determined by relative
proportions of sand, silt and clay
• For each textural class name is
given eg. Sandy clay or sandy clay
loam
3. Textural classes
• Sands - Soils containing70% or more sand
eg. Sang and loamy sand
• Clays –Soils containing more than 35%clay
eg. Sand clay silt clay
• Loams
• Soils containing sand and silt in almost equal
proportions. An ideal loam is composed of
approx. 40 % sand, 40%silt and 20% clay
eg .sandy loam, silt clay loam
Loams are agriculturally the most important
soils for agronomic crops
4.
5. DETREMINATION OF SOIL TEXTURE
• Determined in the field and in lab.
• FIELD
• In the field it is determined by the sense of
feel. The soil is rubbed between the thumb
and fingers in the wet conditions.I
• Sands give a gritty feel
• Silts when dry give a feel of flour and slightly
plastic when wet
• Clays have plastic feel and exhibit stickness
when wet and hardness when dry
6. • In the laboratory
• The most accurate method. determined
through particle size analysis
• Such an analysis gives the amounts sand,Silt
and clay separates in a soil
• To determine textural name we interpolate
the data of particle size analysis in an
equilateral triangle whose base represents
sand the left hand represents clay and the
right silt
• Each side is divided into 100 equal segments
7.
8. Exercise
• To illustrate the use of textural
triangle assume that the soil is
composed of 50% sand,
20%siltand 30% clay. Assign a
textural class
9. IMPORTANCE OF SOIL TEXTURE
• Relative resistance to root
penetration
• Soils with high silt and clay contents
usually retard root growh and extent
of branching. Root penetration is best
is best where surface soil is loose
textured. Why?
10. • ii)Soil fertility Many of the nutrient ions
which plants must extract from soils are
adsorbed by colloids
• The finer the texture of the soil the greater
is its fertility
• iii)Inflitration of water
• Inflitration rates of water entering heavy
soils are low and run off is high
11. • iv) Rate of water movement
• Fine textured soils there is a
resistance to the mass movement of
water
• Down water movement of water
through a sandy soil is so rapid
12. SOIL STRUCTURE
• Soil structure refers to the arrangement of soil
separates into units called soil aggregates.
The smallest aggregate is termed ped
• An aggregate possesses solids and pore
space.
• The arrangement of soil aggregates into
different forms gives a soil its structure.
13. Formation of aggregates
• The natural processes that aid in forming
aggregates are:
1) wetting and drying,
2) freezing and thawing,
3) microbial activity that aids in the decay of
organic matter,
4) activity of roots and soil animals, and
5) adsorbed cations.
14. • The wetting/drying and
freezing/thawing action as well as
root or animal activity push particles
back and forth to form aggregates.
Decaying plant residues and
microbial byproducts coat soil
particles and bind particles into
aggregates.
•
15. • Adsorbed cations help form
aggregates whenever a cation is
bonded to two or more particles.
• Aggregates are described by their
shape, size and stability. Aggregate
types are used most frequently when
discussing structure
16. Structure and soil horizons
• -Structure is one of the defining
characteristics of a soil horizon.
• -A soil exhibits only one structure per
soil horizon, but different horizons
within a soil may exhibit different
structures.
17. • - All of the soil-forming factors, especially
climate, influence the type of structure
that develops at each depth. Granular
and crumb structure are usually
located at the soil surface in the A
horizon. The subsoil, predominantly the
B horizon, has subangular blocky,
blocky, columnar or prismatic
structure.
18. • Platy structure can be found in
the surface or subsoil while single
grain and structureless structure
are most often associated with
the C horizon.
•
19. Soil structure types
• - The type of soil structure is
described on the basis of shape and
arrangements of the peds
• There four principal geometric forms
used to classify types of soil structure
20. – Plate- like
• The aggregates have more developed horizontal
than vertical dimensions giving a flattened
compressed appearance.
• ii)Prism –like
• The vertical axis of the aggregate is more
developed than the horizontal one with
flattened sides giving a pillar- like shape
– This type of aggregate is commonly found in sub soil
horizons of arid and semi arid regions
21. – regions
• Block -like
– All the three dimensions of the aggregate are
of equal size and the aggregate resemble a
block or cube
• - Common in heavy soils of sub humid regions
• iv)Sphere - like
• Aggregates are nearly roundish the axes being
of the same size
22. Soil structural grades
–Characteristic of many surface
soils especially those high in
Organic matter
• - They may have two types of
structures depending upon porosity
of the aggregates
–a)Granular are relatively non –
porous
• b) Crumby which are porous
23. Soil structural grades
• Soil structural grade are recognized
on the basis of stability of the
individual aggregates
• Four grades are designated
• structureless
• There is no noticeable aggregates eg.
loose sand
• Weak
24. Naming of soil structure
• Sequence followed is grade, class
and type
• For example ,If aggregates are
graded as strong classed as fine and
are granular type the soil structure is
designates as strong fine granular
25.
26. Aggregate Stability
– . Stable soil aggregation is a very valuable
property of productive soils. Yet, the stability
of soil aggregation is very reliant on the type
of minerals present in the soil.
– Certain clay minerals form very stable
aggregates, while other clay minerals form
weak aggregates that fall apart very easily
27. • Highly weathered silicate clays,
oxides, and amorphous volcanic
materials tend to form the most
stable aggregates. The presence
of organic matter with these
materials improves stable
aggregate formation.
28. • In nutrient management, the
aggregate stability is important
because well-aggregated
minerals are well drained and
quite workable.
29. • In contrast, less weathered silicate clays,
such as montmorillonite, form weak
aggregates. Some silicate clays are said
to have a shrink-swell potential. This
means that the soil minerals expand, or
swell, when wet, causing the soil to
become sticky and drain poorly. When dry,
these soils shrink and form cracks. The
make-up of the lattice structure of silicate
clays determines the shrink-swell
potential.
•
30. Importance of soil structure
–The soil structure per se is not a
plant growth factor but it influences
all most all plant growth factors
–Water supply, aeration availabity of
plant nutrients, microbial activity
and root penetration are affected by
soil structure
31. – Aggregates are important in a soil because
they influence bulk density, porosity and
pore size.
– The soil structure modifies the influence of
soil texture with regard to moisture and air
relationships. For instance platy structure
normally hinders free drainage. The best
structure for favourable physical properties
soil is either cramby or granular
32. –Pores within an aggregate are
quite small as compared to the
pores between aggregates and
between single soil particles.
This balance of large and small
pores provides for good soil
aeration, permeability and
water-holding capacity.
33. Destruction of aggregates
• -Tillage, falling raindrops and compaction are
primarily responsible for destroying
aggregates.
• As the cutting edge of a tillage implement is
pulled through the soil, the shearing action at
the point of contact breaks apart aggregates.
• The amount of aggregate destruction that
results from tillage depends on the amount of
energy the tillage implement places in the
soil.
34. • The field cultivator has little down
pressure and destroys few
aggregates. The disk, however,
has both cutting action because
of the rotation of the disk and
shearing action. Together there is
substantial down pressure and
destruction.
35. • Aggregates on the soil surface can be
broken down by the beating action of
raindrops. The single particles that were
once part of the aggregate can easily form
a crust when the soil dries. The crust looks
very similar to the crust formed on a
puddle after it rains. It is very difficult for
water to infiltrate a crust and for seedlings
to push up through a crust.
36. • Thus, field operations that lead to
aggregate destruction at the soil surface
have detrimental secondary effects. The
particles also can be eroded if they
become detached by rainfall.
• -Compaction can lead to the breakdown of
aggregates in the surface soil and subsoil
if the applied force from wheel traffic,
animal traffic or human traffic is greater
than the force holding an aggregate
37. Promotion of aggregates
• - Aggregation is promoted by root growth
and the addition of organic material.
Roots excrete compounds that are used
as food by microorganisms. Also, as roots
absorb water and dry the soil, cracks form
along planes of weakness. - Lastly, when
roots decay, root channels serve as
conduits for water that facilitate
wetting/drying and freezing/thawing.
.
38. • - Organic material may be added in the
form of crop residue, animal manure,
sludge, and green manure. These
additions are usually made to the surface
soil and are critical to the development of
granular and crumb structure. As
organic material is incorporated by tillage,
soil animals and microorganisms, it aids in
subsoil structure development
39. SOIL COLOUR
• Most obvious characteristics of soil
• Soil color does not affect the behavior
and use of soil; however, it can indicate
the composition of the soil and give clues
to the conditions that the soil is subjected
to.
• Has no direct effect to plant growth
but it has an indirect one through its
effect in temperature and moisture
40. • Most obvious characteristics of soil
• Soil color does not affect the behavior
and use of soil; however, it can indicate
the composition of the soil and give clues
to the conditions that the soil is subjected
to.
• Has no direct effect to plant growth
but it has an indirect one through its
effect in temperature and moisture
41. • Soil can exhibit a wide range of
colours; gray, black, white, reds,
browns, yellows and under the right
conditions green.
• Predominant soil colours are grey
brown and rust
• Varying horizontal bands of colour in
the soil often identify a specific soil
horizon.
42. Causes of soil colour
• clays have the greatest effect on soil colour
• Humus is black or dark brown iron oxides may
be red or rust brown. Quartz mostly grey or
greyish white
• Soil colour changes with the moisture content.
The more moist the soil is the darker is the
colour because the refractive properties of the
solid components and of the air are very
different and that the light that falls on a dry soil
is largely reflected The refractive properties of
water and soil particles are almost similar
43. • It is therefore desirable to
examine the soil colour when the
sky is clear because the
wavelenghts of the lights are in
constant proportion
44. Significance of soil colour
• The darker the soil the higher is its relative
productivity due to amount of OM present
• Light colour frequently results from
amounts of quatz which has no nutritional
value
• -Practically all soil profiles reveal a change
in colour from one horizon to the next
• In classification of soils colour is very
helpful (soil taxanomy system eg
charnozem (black)
45. • Due to its effect on radiant energy
soil colour also influences other
soil properties Black and dark
colours absorb more heat than
white colours dark soil tend to be
much warmer Implications?
46. Study and classification of soil colour
• Often described by using general
terms, such as dark brown,
yellowish brown, etc., soil colors
are also described more
technically by using Munsell soil
color charts,
47. • which separate color into components of hue
(relation to red, yellow and blue), value
(lightness or darkness) and chroma
(paleness or strength)
• Hue refers to the dominant spectral colour or
quality which distinguishes red from yellow
• Value or brightness expresses apparent
lightness as compared to absolute white
• Chroma defines gradations of purity of color
•
48. Management of soil colour
• Under some conditions it may be
desirable to lower or raise soil temperature
• This may be accomplished by changing
soil colour Effect of crop residues following
decomposition renderes the soil dark in
colour so that during dry season it can
adsorb sunshine energy
49. SOIL TEMPERATURE
• -Is an extremely important property of soil
• - Soil temperature plays an important role
in many processes, which take place in
the soil such as chemical reactions and
biological interactions.
• -It affects plant growth directly and also
influences moisture aeration structure
microbial, enzymic activities,
decomposition of plant residues and the
availability of nutrients
50. • - In temperate climate it is temperature that
limits crop production due to decreased
metabolic activities, Retardation of root
elongation, reduced seed germination
• - Development and activity of microflorareacts
very markedly to temperature variations. Eg.
Below5C nitrification ceases
• How about high temperatures?
51. Factors affecting soil temperature
• -Both external ( environmental) and
internal ( soil) factors affects soil
temperature
• i) Solar radiation
• -The amount of radiation that is
received by soil surface depends on:
• -The insulation by air water vapour ,
clouds snow plants or mulch
52. • -The angle with which the soil faces the
sun which is governed by factors such as
time of the day, latitude and season
•
• ii)Conduction of heat from the atmosphere
• Conduction of heat through air is small. It
can only affect soil temperature only by
contact Therefore air convection or wind is
in the heating up of soil by conduction
from the atmosphere
53. • up of soil by conduction from the atmosphere
• ii)Rainfall-Depending on its temperature rainfall
can cool or warm the soil
• iv) Insulation
• -The soil can be insulated from environmental
temperature by a plant cover, mulch, snow and
fog
• -Insulation serves to maintain a more uniform
soil temperature
54. • v) Biological activity
• - Involves heat. The higher is the activity the
higher the temperature. Eg during composting
• vi)structure, texture and moisture
• Soils in a compacted condition have a more
thermal conductivity than the loose condition
• This is because This is beacusemineral particles
conducts heat better than air
55. • conducts heat better than air
• - A soil in a natural structure has
higher conductivity than recently
disturbed one
• Moisture at the soil surface cools
the soil through evaporation
56. • Soil temperature varies in response to
exchange processes that take place
primarily through the soil surface.
These effects are propagated into the
soil profile by transport processes and
are influenced by such things as the
specific heat capacity, thermal
conductivity and thermal diffusivity.
57. Management of soil Temperature
• Some of the factors influencing soil
temperature can be modified
• An Adjustment of roughness, soil
moisture and soil colour can alter thermal
conductivity
• Mulch and crop residues, plastic paper
have been utilized
• Vegetation keeps the soil relatively cool
by shading the ground
58.
59. Consistency of soils
• Soil consistency is the strength with which
soil materials are held together or the
resistance of soils to deformation and
rupture. Soil consistency is measured for wet,
moist and dry soil samples. For wet soils, it is
expressed as both stickiness and plasticity,
60. • Consistency is the term used to describe the ability of
the soil to resist rupture and deformation. It is
commonly describe as soft, stiff or firm, and hard.
• Water content greatly affects the engineering behavior
of fine-grained soils. In the order of increasing
moisture content (see Figure 2 below), a dry soil will
exist into four distinct states: from solid state, to
semisolid state, to plastic state, and to liquid state. The
water contents at the boundary of these states are
known as Atterberg limits. Between the solid and
semisolid states is shrinkage limit, between semisolid
and plastic states is plastic limit, and between plastic
and liquid states is liquid limit.
61. • Consistency is the term used to describe the ability of
the soil to resist rupture and deformation. It is
commonly describe as soft, stiff or firm, and hard.
• Water content greatly affects the engineering behavior
of fine-grained soils. In the order of increasing
moisture content (see Figure 2 below), a dry soil will
exist into four distinct states: from solid state, to
semisolid state, to plastic state, and to liquid state. The
water contents at the boundary of these states are
known as Atterberg limits. Between the solid and
semisolid states is shrinkage limit, between semisolid
and plastic states is plastic limit, and between plastic
and liquid states is liquid limit.
62. • Consistency is the term used to describe the ability of
the soil to resist rupture and deformation. It is
commonly describe as soft, stiff or firm, and hard.
• Water content greatly affects the engineering behavior
of fine-grained soils. In the order of increasing
moisture content (see Figure 2 below), a dry soil will
exist into four distinct states: from solid state, to
semisolid state, to plastic state, and to liquid state. The
water contents at the boundary of these states are
known as Atterberg limits. Between the solid and
semisolid states is shrinkage limit, between semisolid
and plastic states is plastic limit, and between plastic
and liquid states is liquid limit.
63.
64. • Atterberg limits, then, are water contents at
critical stages of soil behavior. They, together
with natural water content, are essential
descriptions of fine-grained soils.
• Liquid Limit, LL
Liquid limit is the water content of soil in
which
65. • soil grains are separated by water just enough for
the soil mass to loss shear strength. A little higher
than this water content will tend the soil to flow
like viscous fluid while a little lower will cause the
soil to behave as plastic.
• Plastic Limit, PL
Plastic limit is the water content in which the soil
will pass from plastic state to semi-solid state.
Soil can no longer behave as plastic; any change
in shape will cause the soil to show visible cracks.
66. • Shrinkage Limit, SL
Shrinkage limit is the water content in which
the soil no longer changes in volume
regardless of further drying. It is the lowest
water content possible for the soil to be
completely saturated. Any lower than the
shrinkage limit will cause the water to be
partially saturated. This is the point in which
soil will pass from semi-solid to solid state.
67. SOIL TILTH
• Tilth, Physical condition of soil, especially in
relation to its suitability for planting or
growing a crop.
68. • Factors that determine tilth include the
formation and stability of aggregated soil
particles, moisture content, degree of
aeration, rate of water infiltration, and
drainage. The tilth of a soil can change rapidly,
depending on environmental factors such as
changes in moisture
69. • The objective of tillage (mechanical
manipulation of the soil) is to improve tilth,
thereby increasing crop production; in the
long term, however, conventional tillage,
especially plowing, often has the opposite
effect, causing the soil to break down and
become compactedJump to: navigation,
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70. • TILTH Refers to soil general suitability to support plant
growth
• Technically It combines the Physical properties of
particle size, moisture content, degree of aeration,
rate of water infiltration, and drainage into
abbreviated terms in order to more easily present the
agricultural prospects of a piece of land.
• Soils with good tilth has large pore spaces for
adequate water inflitration and water movement
71. Management of soil Tilth
• On Coarse textured soils
-Major limitation in sandy soils is low water and
nutrient holding capacity
-Nutrient leaching particularly N is a problem
-The best management practice is gradual
application of OM
72.
• Fine textured soils, Clayey soils
- Major limitation on such soils is lack of large
pores therefore restricting water and air
movement
- Soils easily waterlog when water cannot move
down the profile
73. - Soils easily waterlog when water cannot move
down the profile
- During irrigation or rainy season the limited
large pore space quickly fills with water
reducing roots oxygen supply
-The best management practice is routine
application of OM which will encourage
favorable microbial decomposition, hence
enhanced pore space
74. Soil Air
• In nutrient management, soil aeration
influences the availability of many nutrients.
Particularly, soil air is needed by many of the
microorganisms that release plant nutrients to
the soil. An appropriate balance between soil
air and soil water must be maintained since
soil air is displaced by soil water.
75. • Air can fill soil pores as water drains or is
removed from a soil pore by evaporation or
root absorption. The network of pores within
the soil aerates, or ventilates, the soil. This
aeration network becomes blocked when
water enters soil pores. Not only are both soil
air and soil water very dynamic parts of soil,
but both are often inversely related:
76. • An increase in soil water content often causes
a reduction in soil aeration.
• Likewise, reducing soil water content may
mean an increase in soil aeration.
• Since plant roots require water and oxygen
(from the air in pore spaces), maintaining the
balance between root and aeration and soil
water availability is a critical aspect of
managing crop plants.
77. • An increase in soil water content often causes
a reduction in soil aeration.
• Likewise, reducing soil water content may
mean an increase in soil aeration.
• Since plant roots require water and oxygen
(from the air in pore spaces), maintaining the
balance between root and aeration and soil
water availability is a critical aspect of
managing crop plants.
78. Composition of soil air
• By comparison to atmospheric air, the soil air
contains more carbon dioxide, less oxygen
and an almost equal amount of nitrogen.
Several other gases are available but in traces
• Variation in composition of soil air exists
depending on place, time and soil itself
80. Factors affecting soil air
• i)Soil properties
• Sol texture, structure and OM have effects on soil
air because they affect air capacity and
permeability in the soil
• Granular soils contain less than one half as much
CO2 as structureless soils . Loams contain more
CO2 than sands Usually the amount of CO2 and
that of O2 decreases with depth
81. • The presence of growing plants tend to reduce
O2 of the soil and to increase the amount of CO2
due to respiration of roots The CO2 content of
the soil tend to increase by manuring
iii) Biological activities
• Addition of organic material in the soil enhances
biological activities
• In decomposion of organic molecules, O2 is
utilized and CO2 is evolved
82. iv) Seasonal variations
• Variations in temperature and moisture causes
variations in soil air
• Renewal of soil air
• For proper aeration the gases should freely
interchange between the soil and the
atmosphere
• Inadequate interchange may have effects in root
respiration
• Exessive moisture conditions restrict aeration
83. Factors affecting renewal of soil air
• These are: rainfall, temperature, pressure and
wind
• Entry of Entry of rain water in the soil causes
displacement of the soil air from the pores
84. • How do other factors affect renewal of soil air?
Importance of soil air
• O2 is required for respiration of plant roots
microbes and soil fauna
• CO2 helps to dissolve the nutrients from rocks
and minerals
• The N2 Of soil air may be fixed by symbiotic and
non symbiotic organisms and utilized by higher
plants
85. Management of soil air
• Proper aeration is needed for proper crop
production
• Physical properties eg. stricter, moister and
temperature should be made favorable for good
aeration
• Generally, open structure, low moisture content
and high temperatures increases diffusion rates.
Addition of OM, tillage practices and mulch
increases aeration
86. Table 4. Soil Oxygen and Carbon Dioxide
Content at Various Depths (Trinidad)
87. Soil Atmosphere
• The soil atmosphere is not uniform
throughout the soil because there can be
localized pockets of air.
• The relative humAir in the soil often contains
several hundred times more carbon dioxide.
• Humidity of soil air is close to 100%, unlike
most atmospheric humidity.
88. SOIL DENSITY
DEFINITION
• Density, as applied to any kind of
homogeneous monophasic material of mass
M and volume V, is expressed as the ratio of
M to V. Under specified conditions, this
definition leads to unique values that
represent a well-defined property of the
material.
89. • The density of the soil can be expressed
either by particle (true) density or as bulk
density (apparent)
• -Particle density is related to the solid portion
of the soil mass only
• It is defined as the weight per unit volume of
the solids. Ranges from 2.4 to 2.75 g/cc
90. • Particle density is the volumetric mass of the solid soil.
It differs from bulk density because the volume used
does not include pore spaces.
• Particle density = oven-dry soil weight / volume of soil
solids
• Particle density represents the average density of all
the minerals composing the soil. For most soils, this
value is very near 2.65 g/cm3 because quartz has a
density of 2.65 g/cm3 and quartz is usually the
dominant mineral. Particle density varies little
between minerals and has little practical significance
except in the calculation of pore space.
91. Bulk density
• It is total volume of soil occupied by both
solids and pores
• Measured by determining the oven dry weight
of an undisturbed core of soil of known
volume
• The BD of soil is always smaller than its
particle density ( Why)
92. • The magnitude decreases with finess in
texture
• Loose porous soils have low BD. BD is altered
by cropping practices. Intensive cultivation
makes the soil more compact and increases
weight per unit volume
93. Porosity
• Porosity or pore space refers to the volume of
soil voids that can be filled by water and/or
air. It is inversely related to bulk density.
Porosity is calculated as a percentage of the
soil volume:
• Bulk density x 100 = % solid space
Particle density
• 100% – % Solid Space = Percent Pore Space
94. Sample Calculation 1
• A 260 cm3 cylindrical container was used to
collect an undisturbed soil sample. The
container and soil weighed 413 g when dried.
When empty the container weighed 75 g.
What is the bulk density and porosity of the
soil?
95. • A. To determine bulk density:
• Sample Volume = 260 cm3; Sample Weight =
413 - 75 = 338 g ; Bulk density = 338 g/260
cm3= 1.3 g /cm3
• B. To determine porosity:
• Bulk density = 1.3 g /cm3; Particle density =
2.65 g /cm3; Porosity = 100 - (1.3/2.65 x 100)
= 51%
96. • Sample calculation 2
• Given the following information:
• -Total volume of core = 98.2g/cc
• -Saturated weight =185g
• -Oven dry weight =150g
97. • a) Calculate porosity
• Porosity = Total pore volume/Total volume
• Pore volume water volume at saturation – water
volume at oven dry weight
• Volume of water = weight of soil
• Therefore, 185g – 150g =35g
• Wight of water is therefore 35g and pore volume
is 35g/cc
• Porosity is therefore 35/98.2 = 0.36
98. • b) Calculate Bulk density and particle density
( take home assignment)
99. SOIL WATER CONTENT
( WETNESS)
• Water content or moisture content is the
quantity of water contained in a material,
such as soil (called soil moisture), is expressed
as a ratio, which can range from 0 (completely
dry) to the value of the materials' porosity at
saturation. It can be given on a volumetric or
mass (gravimetric) basis.
100. • ENERGY STATE OF SOIL WATER
•
• -Soil water can contain energy in different quantities
and forms.
• -There are two forms of energy, kinetic and potential
• Movement of water in the soil is quite slow, its KE
which is proportional to proportional to the velocity
squared is considered to be negligible
• -The potential energy which is due to position or
internal condition is important in determining the state
and movement of water in the soil
101. • -The potential energy of soil water varies over a very wide
range
• -Differences in PE of water between one point and another
give rise to the to the tendency of water to flow with
• Movement is from where the PE is higher to where it is
lower
• -The rate of decrease of PE with distanceis infact the
moving force causing flow in the soil
• -The force acting on soil water directed from a zone of
higher to the lower potential is equal to the negative
potential gradient (-dq/dx) which is the change of energy
potential with distance x. The negative sign indicates that
the force acts in the direction of decreasing potential
102. • Water Potential (Ψ)
• Most of the issues about soil water relate to
its energy state and its movement (e.g. Evapo
transpiration and Deep Drainage).
• -Therefore, water moves constantly in
direction of potential energy (i.e. wet to dry
soil), where the gradient of potential energy
with distance is the moving force causing flow.
103. • In soil, the reference state is the energy level of water in
the soil at saturation. That is, when all pores are filled with
water. At this point soil water potential (Ψ) is nominally
zero (~0). In most cases, however, soil water potential (Ψ)is
less than zero. This is indicated by giving soil water
potential (Ψ) a negative sign (-ve).
• In practical terms, and as the soil dries out soil water
potential (Ψ)decreases and becomes increasingly more -ve.
So that when soil water potential (Ψ) is “high” it means Ψ
is less –ve and is therefore very close to 0. When soil water
potential (Ψ)is high it means soil water is
held loosely,
highly available and
ready to move somewhere else.
105. • Water retention curve is the relationship
between the water content, θ, and the soil water
potential, ψ. This curve is characteristic for
different types of soil, and is also called the soil
moisture characteristic.
• It is used to predict the soil water storage, water
supply to the plants (field capacity) and soil
aggregate stability. Due to the hysteretic effect of
water filling and draining the pores, different
wetting and drying curves may be distinguished.
106. • The general features of a water retention curve
can be seen in the figure, in which the volume
water content, θ, is plotted against the matric
potential, . At potentials close to zero, a soil is
close to saturation, and water is held in the soil
primarily by capillary forces. As θ decreases,
binding of the water becomes stronger, and at
small potentials (more negative, approaching
wilting point) water is strongly bound in the
smallest of pores, at contact points between
grains and as films bound by adsorptive forces
around particles
107. • Sandy soils will involve mainly capillary binding,
and will therefore release most of the water at
higher potentials, while clayey soils, with
adhesive and osmotic binding, will release water
at lower (more negative) potentials. At any given
potential, peaty soils will usually display much
higher moisture contents than clayey soils, which
would be expected to hold more water than
sandy soils. The water holding capacity of any soil
is due to the porosity and the nature of the
bonding in the soil.
108. • Soil moisture characteristic curve is strongly affected by soil
texture. The graeter the clay content, in general, the greater the
water retension at any particular sunction and the more gradual
the slope of the curve
• -In a sandy soil most of the pores are relatively large and once
these pores are emptied at a given suction only a small amount of
water remains
• -In a clay soil the pore size distribution is is more uniform and more
water is adsorbed so that increasing increasing the matric suction
causes a more gradual decrease in water content ( See figure
below)
•
• -Soil structure also influences the shape of the curve particularly in
the suction range-Effect of compaction is to reduce total porosity
109. Water flow
• Soil contains a large distribution of pore sizes
and channels through which water flows. The
flow of water (i.e. liquid) in soil is important
for calculations of water balance and
redistribution of solutes and energy within
soil-plant-atmosphere system.
110. • Flow rate also depends on hindrances; friction
between water and particle surfaces as well as
pore constrictions and other interruptions in
flow path.
• It is generally recognized that three types of
water movement occur in soil;
• Saturated,
• Unsaturated, and
• Vapour
111.
112. • Saturated Hydraulic Conductivity
• Saturated flow occurs when soil pores are
completely filled with water Saturated flow in
soil with large continuous pores can be rapid if
driven by large differences in gravity and
pressure.
113. • Unsaturated flow is generally rapid through
fine sand or well aggregated loams (medium
sized pores) and slower through very fine and
poorly aggregated clayey soil (very small
pores).
• Vapour flow occurs only in relatively dry soil
where vapour pressure differences are
significant.
114. • Field capacity
• Field Capacity is the amount of soil moisture or
water content held in the soil after excess water
has drained away and the rate of downward
movement has decreased. This usually takes
place 2–3 days after rain or irrigation in pervious
soils of uniform structure and texture. The
physical definition of field capacity (expressed
symbolically as θfc) is the bulk water content
retained in soil at −33 J/kg (or −0.33 bar) of
hydraulic head or suction pressure.
115. • Permanent wilting point (PWP) or wilting point (WP)
is defined as the minimal point of soil moisture the
plant requires not to wilt. If moisture decreases to this
or any lower point a plant wilts and can no longer
recover its turgidity when placed in a saturated
atmosphere for 12 hours. The physical definition of the
wilting point (symbolically expressed as θpwp or θwp) is
defined as the water content at −1500 J/kg of suction
pressure, or negative hydraulic head.
• However, it is noted that the PWP values under field
conditions are not constant for any given soil but are
determined by the integrated effects of plant, soil, and
atmospheric conditions.