agriculture electronics for engineering students

Handled by,
Dr. R. Jenitha
Assistant Processor, ECE Dept,
P.S.R. Engineering College

aypy7hw
7/18/2024
191OE2A - Agriculture Electronics 2

SOIL TEXTURE
Soil texture refers to the relative percentage of sand,
silt and clay in a soil.
The proportion of each size in a given soil (the texture)
cannot be easily altered and it is considered as a basic
property of a soil.
The soil separates are defined in terms of diameter in
millimeters of the particles.
Soil particles less than 2 mm is called fine earth and
are excluded from soil textural determinations.
SOIL TEXTURE

SOIL TEXTURAL CLASSES
Sand: It includes all soils in which the sand separates make up at
least 70% of the material by weight.
Silt: It includes soils with at least 80% silt and 12% or less clay.
Particle size intermediate between sand and clay.
Clay: It includes soils with at least 35-40% clay separate.
SOIL TEXTURE

THE TEXTURAL TRIANGLE
SOIL TEXTURE

METHODS OF TEXTURAL DETERMINATION
1. Feel Method : Texture is commonly determined by the
sense of feel.
 Sand feels gritty and its particles can be easily seen
 Silt(when dry) feels like flour/ talcum powder ; and is
slightly plastic when wet
 Clay feels very plastic and is very sticky when wet and hard
under dry conditions
2. Laboratory method :
i) Elutriation method – Water & Air
ii) Pipette method
iii) Decantation/ beaker method
iv) Test tube shaking method
SOIL TEXTURE

SOIL TEXTURE
Influence of Soil Texture Separates on Some Properties of Soils
Property/behavior Sand Silt Clay
Water-holding capacity Low Medium to high High
Aeration Good Medium Poor
Drainage rate High Slow to medium Very slow
Soil organic matter level Low Medium to high High to medium
Decomposition of organic
matter
Rapid Medium Slow
Warm-up in spring Rapid Moderate Slow
Compactability Low Medium High
Shrink/Swell Potential Very Low Low
Moderate to very
high
Ability to store plant
nutrients
Poor Medium to High High

SOIL STRUCTURE
The arrangement of primary particles (sand, silt, clay) and their
aggregates into a certain definite pattern is called soil structure.
Influence of soil structure on soil physical properties:
Aeration/ Porosity
Temperature
Density
Consistency
Colour
Etc.
SOIL
STRUCTURE

I. TYPES OF SOIL STRUCTURE
1. Platy: Peds are flattened one atop the other; 1–10 mm thick.
Found in the A-horizon of forest soils and lake sedimentation.
2. Prismatic and Columnar: Prismlike peds are long in the
vertical dimension; 10–100 mm wide. Prismatic peds have flat
tops, columnar peds have rounded tops. Tend to form in the B-
horizon in high sodium soil where clay has accumulated.
SOIL
STRUCTURE
PLATY SOIL COLUMNAR
PRISMATIC

3. Angular and subangular: Blocky peds are imperfect
cubes, 5–50 mm, angular have sharp edges,
subangular have rounded edges. Tend to form in the
B-horizon where clay has accumulated and indicate
poor water penetration.
4. Granular and Crumb: Spheroid peds of
polyhedrons, 1–10 mm, often found in the A-horizon
in the presence of organic material. Crumb peds are
more porous and are considered ideal.
SOIL
STRUCTURE
ANGULAR SUB ANGULAR GRANULAR

II. CLASSES OF SOIL STRUCTURE
SOIL
STRUCTURE
PLATY &
SPHERICAL
BLOCKY PRISMLIKE
1. Very fine or very thin <1 mm <5 mm <10 mm
2. Fine or thin 1–2 mm 5–10 mm 10–20 mm
3. Medium 2–5 mm 10–20 mm 20-50
4. Coarse or thick 5–10 mm 20–50 mm 50–100 mm
5. Very coarse or very
thick
>10 mm >50 mm >100 mm

III. GRADES OF SOIL STRUCTURE
1. Structureless: No aggregation or orderly
arrangement. Soil is entirely cemented
together in one great mass.
2. Weak: Poorly formed; Non-durable. Weak
cementation allows peds to fall apart.
3. Moderate: Well formed; moderately durable.
Indistinct in undisturbed soil but may break
into aggregates. This is considered ideal.
4. Strong: Well formed; durable. Peds are distinct
before removed from the profile and do not
break apart easily.
SOIL
STRUCTURE

FACTORS AFFECTING SOIL STRUCTURE
1.Climate: Climate influences the degree of aggregation as well as on the
type of soil structure.
In arid regions there is very little aggregation.
In semi arid regions, the degree of aggregation is greater.
2. Organic matter: Organic matter improves the structure of sandy soil &
clay soil.
In case of sandy soil, the sticky and slimy material produced by
decomposing om cement the sand particles together to form aggregates.
In case of clayey soil, it modifies the properties of clay by reducing its
cohesiveness. This helps make clay more crumby.
3. Adsorbed cations: Aggregate formation is influenced by nature of
cation adsorbed.
Na⁺ --- Deflocculation --- Poor structure
Ca²⁺ --- Flocculating --- Good structure
SOIL
STRUCTURE

4. Tillage: Intensive cultivation increased infiltration capacity and
penetrability, but spolied soil structure. For obtaining good soil structure,
tillage operation should be made at optimum moisture conditions.
5. Type of vegetation: Grasslands and forest soils have high stability of
aggregates.
6. Animals: Among the soil fauna small animals like earthworms, moles
and insects etc., that burrow in the soil are the chief agents that take part
in the aggregation of finer particles.
7. Microbes: Algae, fungi, actinomycetes and fungi keep the soil particles
together.
8. Fertilizers: Fertilizer like Sodium Nitrate destroys granulation by
reducing the stability of aggregates. Few fertilizers for example, CAN
help in development of good structures.
9. Wetting and drying: When a dry soil is wetted, the soil colloids swell on
absorbing water. On drying, shrinkage produces strains in the soil mass
gives rise to cracks, which break it up into clods and granules of various
sizes.
SOIL
STRUCTURE

ROLE OF SOIL STRUCTURE IN RELATION TO
PLANT GROWTH
Soil structure influences the amount and nature of porosity.
Structure controls the amount of water and air present in the soil.
It affects tillage practices.
Structure controls runoff and erosion.
Platy structure normally hinders free drainage whereas sphere like structure
(granular and crumby) helps in drainage.
Crumby and granular structure provides optimum infiltration, water holding
capacity, aeration and drainage.
It also provides good habitat for microorganisms and supply of nutrients.

1. Soil texture
2. Soil porosity
3. Soil chemistry
4. Soil color
5. Soil permeability
6. Consistence
7. Particle density
8. Bulk density
9. Pore space
10. Atterberg limits

SOIL PROFILE:
A verticalexposure of the horizon sequenceof the soil is termed a
soil profile.
The layers that make up a soil profile are called horizons.
The Horizons are identifiedby the lettersA, E, B, C, O and R.
Each zone has a differentcomposition, and has differentinfluences
on what type of lifethat soil can support.

The Texture refers to the relativeamount of sand, silt, and clay in
the soil.
The particlesthat make up soil are categorized into three groups by
size – sand, silt, and clay.
Sand are the largestparticlesand feel “gritty”
Siltare medium sized and feel soft, silkyor “floury”
Clay are the smallestsized particlesand feel“sticky”
Soil containingequal amount of sand, slitand clay is called “Loam”.
SANDSLIT CLAY

The proportions of differentsizedmineral particlesin the soil or the
relativeamount of sand, silt, and clay present in the soil expressed
as percentages.
SOIL TEXTURALCLASSES:
Textural classificationof soil means classificationof soilson the
basisof theirtexture into differentgroups or classessuchas Sand,
Sandy-loam and Siltyloam.
The broad and fundamental groups of soil textural classesare
recognized as Sands, Siltand Clays.
There are 12 textural classcategories.

IMPORTANCE:
Soil texture is one of the most important properties of a soil, and it
greatly affectsland use and management.
It affectsthe amount of water and nutrientsthat a soil can hold and
supply to plants.
Soil physicalproperties such as structure,and movement of air and
water through the soil are affectedby texture.

The arrangement of particlesin the soil mass is calledsoil
structure.
Soil structurealso be definedas aggregates into which soil breaks
up. OR
Simply, The way in which soil particlesare grouped or bound
together to form lumps or aggregatesis known as soil structure.
The primary soil particlessuch as sand, siltand clay usually occur
grouped together in the form of aggregates.
Natural aggregates are called peds whereas artificialaggregates
are called clods.

Clods are formed due to disturbanceof the fieldby ploughing or
digging.
The words fragmentationand concretions are often used in
connectionwith the structure of soil.
Fragment isa broken peds whereas when salts dissolvedin
percolatingwater precipitate,it results in the formation of
concretions.
The soil conditions and characteristicssuch as water movement,
heat transfer, aeration, bulk density and porosity will be much more
influencedby structure.

IMPORTANCE:
Soil structureis one of the most important soil’s physicalfactors
controlling or modulating the flow and retention of water, solutes,
gases, and biota in agriculturaland natural ecosystems.
Soil structureis very important in soil productivityand is a limiting
factor of crop yield.
Soil structurecontrols many processes in soils. It regulateswater
retentionand infiltration,gaseous exchanges, soil organic matter
and nutrientdynamics, root penetration, and susceptibilityto
erosion.

Soil color is one property that can be used to describehorizonation and
soil morphology.
The change in soil color with depth is directlyrelated to a varietyof
processes that are occurring in the soil
The colour of soils is due to the colour of their constituents.
For example:
Black coloured soils are rich in organic matter and therefore fertile.
Red coloured soils are rich in ferric oxide
Yellow color is due to hydrated iron oxides and hydroxide.
The colour of a soil is inheritedfrom its parent rock material.
As for example, red soil developed from red sand stone and sand
developed from quartz.

Soil color is describedby the parameters calledHue, Value and Chroma.
Hue representsthe dominant wave length or color of the light.
Value, refers to the lightnessof the color.
Chroma, relativepurity or strength of the color.
The colour of the soil in terms of the above parameters could be quickly
determined by comparison of the sample with a standard set of colour
chipsmounted in a note-book called MUNSELL SOIL COLOUR CHARTS
(Munsell Soil Colour Charts, 1973).

IMPORTANCE:
Color is an important characteristicused in the identificationof soil
conditions that affectthe value of land for agriculturaluses.
Soil color givesan indicationof the various processes going-on in the soil
as well as the type of mineralsin the soil.
The colour of a soil is an indicationof the nature of an individualsoil.
The soil color does not effectthe behavior of the soils, but provides
insightsinto environmental conditions, formation processes, and other
Influenceson the soil.
Soil color is also used to for classificationof soils.

The Soil Densityis definedas the property of soil, suggestinghow closely
the soil grainswill be arranged withinthe volume of soil.
There can be spacesbetween particles,containingair and water.
Soil density isexpressed in two well acceptedconcepts which are,
1. Particledensity
2. Bulk density

PARTICLEDENSITY: (Also termed as true density)
The weight per unitvolume of the solid portion of soil is called Particle
density. It refers to only the solids excludingthe voids.
In the metric system, particledensitycan be expressed in terms of mega
grams per cubicmeter (Mg/m3).
Generallyparticledensityof normal soils is 2.65 grams per cubic
centimeter.
The particledensity is higherif large amount of heavy mineralssuch as
magnetite; limoniteand hematite are present in the soil.
With increasein organic matter of the soil the particledensity decreases.

BULK DENSITY: (Also calledas apparent density)
Bulk density is considered as the total mass of the soil (includeswater
present) dividedby soil volume.
OR
The oven dry weightof a unit volume of soil inclusiveof pore spacesis
called Bulk density.
The bulk density of sandy soil is about 1.6 g / cm3, whereas that of organic
matter is about 0.5.
The bulk density of a soil is always smallerthan its particledensity.
Bulk density normally decreases,as mineral soils become finer in texture.

IMPORTANCE:
Soil density isimportant from the point of view of plant growth especially
root penetration.
A shallow plant root and poor plant growth resultingfrom compacted and
high bulk density soils willinfluencecrop yield and reduce vegetative
cover availableto protect soil from erosion.
Bulk density reflectsthe soil’sabilityto functionfor structuralsupport,
water and nutrient and microbial lifemovement, and soil aeration.

Porosity refers to how many pores, or holes, a soil has.
The porosity of a soil isexpressed as a percentageof the total volume of
the soil material.
The space between particlesis called pore space which determines the
amount of water that a givenvolume of soil can hold.
Pore spacesbetween the aggregatesof soil particlesare macro pores
Pore spacesbetween the individualparticlesof the aggregates are micro
pores.
Mainly, pore spacesfacilitatethe availabilityand movement of air or water
withinthe soil environment.

POROSITY IN SANDY AND CLAY SOILS:
Sandy soils have a higher percentageof macro pores.
Typically,moisture content in sandy soils is relativelylow when compared
to clay soils.
Whereas,
Clay soils contain a higher percentagemicro pores when compared to
sandy soils.
Clay soils are more susceptibleto water logging whichcan adversely
affectroot respirationand microbial activity.

IMPORTANCE:
Porosity is one of the major important property of the soil as it facilitates
the storage of water availabilityof air within the soil.
Porosity also affectsthe structure and consistencyof the soil.
It helps the plant roots to grow further move easilywithinthe soil
environment.
Porosity is a main indicatorof soil structuralquality. Therefore, its
characterizationis essentialfor assessingthe impactof addingorganic
matter to a soil system.

Soil consistenceis defined as a term to designatethe manifestationof
physicalforces of cohesion and adhesion actingwithinthe various levelof
moisture content.
It is the physical conditionof the soil at various moisture content as
evidenced by the behavior of that soil toward mechanicalstressesor
manipulation.
The manifestationas statedin the definitionincludesas follows:
i. Behavior of the soil towards gravity, pressure, thrust and pull.
ii. Tendency of the soil mass to adhere to foreign bodies.
iii. Tactilequality of soil on rubbing between the fingers.

SOIL TILLAGE:
Tillageis the physicalmanipulationof soil with tools and implementsto
result in good tilthfor bettergermination of seedsand subsequentgrowth
of crops.
Tillagehelps to replace natural vegetationwith useful crop and to improve
the physical conditionof soil, control of weeds, insect-pestsand diseases
and also bring the nutrientavailableto plant.
The cultivationis not possible without tillageoperation.

SOIL COMPACTION:
Soil compaction is the process of increasingdry bulk density of soil,
reducingthe pore space by expulsion of air through appliedpressure on a
soil body. Under very high pressure, the soil particlesmay themselvesbe
compressed but only slightly.
Compaction due to the machinesused for tillageof land, harvestingand
threshingof crops has adverse effectson the growth of plantsdue to
reduced aerationand increasedbulk density of the soil.
Compaction of the soil may also be due to grazingof animals,human
activitiesin the fieldand intense rainfallas well as irrigation.

IMPORTANCE:
Soil consistenceprovides a means of describingthe degree and kind of
cohesion and adhesion between the soil particlesas relatedto the
resistanceof the soil to deform or rupture.
Consistenceis an important characteristicof the soil as affectsthe nature
of force betweenparticlesof the soil.
It is important for Tillage or trafficconsideration.

Soil micro-organisms show maximum growth and activityat optimum soil
temperature range.
Allcrops practicallyslow down theirgrowth below the temperature of
about 9Â°C and above the temperature of about 50Â°C.
The biological processesfor nutrient transformations and nutrient
availabilityare controlled by soil temperature and soil moisture.

Sources of Soil Temperature are:
1) SOLARRADIATION:
The main source of heat is the sun. The temperature of the soil is primarily
dependentupon the amount of radiant energy received from the sun.
The sunrays reach the earth after they pass through the atmosphere and
warms the surfaceof the soil on which they fall.
A part of soil temperature is lost to the air by radiation.

2) CONDUCTION:
The heat is absorbed from solar radiation by surface soil and is conducted
down the depth of the soil.
The interiorof the earth is very hot, the conductionof thisheat to the soil is
very slow.
3) BIOLOGICALAND CHEMICALREACTION:
In a soil, various biologicaland chemicalreactionoccurs. As a result,
some amount of heat is liberatedin the soil due to biologicaland chemical
reaction.

IMPORTANCE:
Soil temperature is important to growers, especiallyfor spring planting.
Many seeds need a certainminimum temperature for germination.
Soil temperature has a profound influenceon seed germination, root and
shoot growth, and nutrient uptake and crop growth.
Seedsdo not germinate below or above a certainrange of temperature but
micro-organism functioning in the soil is very activewhile a certain range
of temperature, which is about 27Â° to 32Â°C.

The Atterberg Limits are: the shrinkage limit, plastic limit, and liquid limit. In
addition, there is the commonly referred to ‘PlasticityIndex’:
The Shrinkage Limit (SL) is the water content where further loss of moisture
willnot result in any more volume reduction.
The Plastic Limit (PL) is minimum water content at which a soil is considered
to behave in a ‘plastic’manner, i.e. is capable of being moulded.
• The Liquid Limit (LL) is the maximum water content a silt or clay can have
before becoming a liquid, i.e. turning into mud.
• The Plasticity Index (PI) is the range of moisture contents where the silt or
clay remains plastic(PI = LL – PL).

• Soil formation or pedogenesis, is the combined effect of human impact on
environment, physical, chemical and biological processes working on soil
parent material.
• Climate regulates soil formation. Soils are more developed in areas with
higher rainfalland more warmth.
• The rate of chemical weathering increases by 2-3 times when the
temperature increasesby 10 degree Celsius.

• Addition
• Loss
• Translocation
• Transformation

• Water from rainfall.
• O2 & CO2 from the atmosphere.
• OM from decomposition of plants & animals
residues.
• Eroded materials from sediments
• Nutrients or ions from rain water, atmosphere,
etc.
• Energy from sunlight

• Water through evapotranspiration.
• Nitrogen by denitrification & volatilization.
• O2 & CO2 through oxidation of OM.
• Soil by erosion
• Water & nutrients by leaching.
• Energy by radiation.

• Salts that are dissolvedin water.
• Nutrients that cyclein plants.
• Soil by animals,e.g..Earthworms

• It is the mobilization and translocation of certain
constituent’s viz. Clay, Fe2O3, Al2O3, SiO2, humus,
CaCO3, other salts etc. from one point of soil body to
another.
• It is the process of removal of constituents in
suspension or solution by the percolating water from
the upper to lower layers. The horizon formed by the
process of eluviation is termed as eluvial horizon (A2 or
E horizon).

agriculture electronics for engineering students

FUNDAMENTAL SOIL
FORMING PROCESS
Humification is the process of
decomposition of organic matter and
synthesis of new organic substances.
It is the process of transformation of
raw organic matter into formation of
surface humus layer, called Ao-
horizon.
The percolating water passing through
this layer dissolves certain organic
acids and affects the development of
the lower A-horizon and the B-

FUNDAMENTAL SOIL
FORMING PROCESS
 Eluviation is the process of removal
of constituents by percolation from
upper layers to lower layers.
 This layer of loss is called eluvial and
designated as the A-horizon. The
eluviated producers move down and
become deposited in the lower
horizon which is termed as the
illuvial or B-horizon.
 The eluviation produces textural
differences. The process of illuviation
leads to the textural contrast
between A2 and B1 horizon.

The development of all the horizons in soil is termed as
horizonation.
In the favorable conditions it take about 250 years but in
adverse conditions take even 1000 years.

Which of the following is NOT a factor of soil formation?
• A) Climate
• B) Parent material
• C) Topography
• D) Pollution
What is the primary role of parent material in soil formation?
A) Determining soil color
B) B) Providing mineral content
C) C) Influencing soil pH
D) D) All of the above

 Which soil horizon is typically known as the topsoil?
• A) O horizon
• B) A horizon
• C) B horizon
• D) C horizon
 Which process involves the breakdown of rocks into smaller particles to form soil?
• A) Erosion
• B) Leaching
• C) Weathering
• D) Sedimentation

 Humus is an important component of soil because it:
• A) Increases water retention
• B) Provides essential nutrients
• C) Improves soil structure
• D) All of the above

 What term is used to describe the amount of water soil can hold against gravity?
• A) Field capacity
• B) Wilting point
• C) Saturation
• D) Permeability
 At which point do plants start to wilt because they cannot extract water from the
soil?
• A) Field capacity
• B) Wilting point
• C) Saturation point
• D) Hygroscopic point

 Which type of soil typically has the highest water-holding capacity?
• A) Sandy soil
• B) Silty soil
• C) Clay soil
• D) Loamy soil
 What does the term "percolation" refer to in soil science?
• A) The movement of air through soil
• B) The downward movement of water through soil
• C) The absorption of water by plants
• D) The evaporation of water from the soil surface

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