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
4. The word soil is derived from a Latin word ‘solum’
meaning earthy material in which plants grow.
Soil may be defined as “the part of earth crust in which
humus is present”.
OR
Soil is a natural body developed by natural forces acting
on natural materials.
OR
Soil can be defined as the organic and inorganic materials
on the surface of the earth that provide the medium for
plant growth.
5. SOIL PROFILE:
A vertical exposure of the horizon sequence of the soil is
termed a soil profile.
The layers that make up a soil profile are called horizons.
The Horizons are identified by the letters A, E, B, C, O and
R.
Each zone has a different composition, and has different
influences on what type of life that soil can support.
6. The Texture refers to the relative amount of sand, silt, and
clay in the soil.
The particles that make up soil are categorized into three
groups by size – sand, silt, and clay.
Sand are the largest particles and feel “gritty”
Silt are medium sized and feel soft, silky or “floury”
Clay are the smallest sized particles and feel “sticky”
Soil containing equal amount of sand, slit and clay is
called “Loam”.
SANDSLIT CLAY
7. The proportions of different sized mineral particles in the
soil or the relative amount of sand, silt, and clay present in
the soil expressed as percentages.
SOIL TEXTURAL CLASSES:
Textural classification of soil means classification of soils
on the basis of their texture into different groups or
classes such as Sand, Sandy-loam and Silty loam.
The broad and fundamental groups of soil textural classes
are recognized as Sands, Silt and Clays.
There are 12 textural class categories.
8. IMPORTANCE:
Soil texture is one of the most important properties of
a soil, and it greatly affects land use and
management.
It affects the amount of water and nutrients that a soil
can hold and supply to plants.
Soil physical properties such as structure, and
movement of air and water through the soil are
affected by texture.
9. The arrangement of particles in the soil mass is called soil
structure.
Soil structure also be defined as aggregates into which
soil breaks up. OR
Simply, The way in which soil particles are grouped or
bound together to form lumps or aggregates is known as
soil structure.
The primary soil particles such as sand, silt and clay
usually occur grouped together in the form of aggregates.
Natural aggregates are called peds whereas artificial
aggregates are called clods.
10. Clods are formed due to disturbance of the field by
ploughing or digging.
The words fragmentation and concretions are often used
in connection with the structure of soil.
Fragment is a broken peds whereas when salts dissolved
in percolating water precipitate, it results in the formation
of concretions.
The soil conditions and characteristics such as water
movement, heat transfer, aeration, bulk density and
porosity will be much more influenced by structure.
11. IMPORTANCE:
Soil structure is one of the most important soil’s physical
factors controlling or modulating the flow and retention of
water, solutes, gases, and biota in agricultural and natural
ecosystems.
Soil structure is very important in soil productivity and is a
limiting factor of crop yield.
Soil structure controls many processes in soils. It
regulates water retention and infiltration, gaseous
exchanges, soil organic matter and nutrient dynamics,
root penetration, and susceptibility to erosion.
12. Soil color is one property that can be used to describe
horizonation and soil morphology.
The change in soil color with depth is directly related to a
variety of 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 inherited from its parent rock material.
As for example, red soil developed from red sand stone and
sand developed from quartz.
13. Soil color is described by the parameters called Hue, Value and
Chroma.
Hue represents the dominant wave length or color of the light.
Value, refers to the lightness of the color.
Chroma, relative purity 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 chips mounted in a note-book called
MUNSELL SOIL COLOUR CHARTS (Munsell Soil Colour
Charts, 1973).
14. IMPORTANCE:
Color is an important characteristic used in the identification of
soil conditions that affect the value of land for agricultural uses.
Soil color gives an indication of the various processes going-on
in the soil as well as the type of minerals in the soil.
The colour of a soil is an indication of the nature of an individual
soil.
The soil color does not effect the behavior of the soils, but
provides insights into environmental conditions, formation
processes, and other Influences on the soil.
Soil color is also used to for classification of soils.
15. The Soil Density is defined as the property of soil, suggesting
how closely the soil grains will be arranged within the volume of
soil.
There can be spaces between particles, containing air and
water.
Soil density is expressed in two well accepted concepts which
are,
1. Particle density
2. Bulk density
16. PARTICLE DENSITY: (Also termed as true density)
The weight per unit volume of the solid portion of soil is called
Particle density. It refers to only the solids excluding the voids.
In the metric system, particle density can be expressed in terms
of mega grams per cubic meter (Mg/m3).
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.
17. BULK DENSITY: (Also called as apparent density)
Bulk density is considered as the total mass of the soil (includes
water present) divided by soil volume.
OR
The oven dry weight of a unit volume of soil inclusive of pore
spaces is 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 smaller than its particle
density.
Bulk density normally decreases, as mineral soils become finer
in texture.
18. IMPORTANCE:
Soil density is important from the point of view of plant growth
especially root penetration.
A shallow plant root and poor plant growth resulting from
compacted and high bulk density soils will influence crop yield
and reduce vegetative cover available to protect soil from
erosion.
Bulk density reflects the soil’s ability to function for structural
support, water and nutrient and microbial life movement, and
soil aeration.
19. Porosity refers to how many pores, or holes, a soil has.
The porosity of a soil is expressed as a percentage of the total
volume of the soil material.
The space between particles is called pore space which
determines the amount of water that a given volume of soil can
hold.
Pore spaces between the aggregates of soil particles are macro
pores
Pore spaces between the individual particles of the aggregates
are micro pores.
Mainly, pore spaces facilitate the availability and movement of
air or water within the soil environment.
20. POROSITY IN SANDY AND CLAY SOILS:
Sandy soils have a higher percentage of macro pores.
Typically, moisture content in sandy soils is relatively low when
compared to clay soils.
Whereas,
Clay soils contain a higher percentage micro pores when
compared to sandy soils.
Clay soils are more susceptible to water logging which can
adversely affect root respiration and microbial activity.
21. IMPORTANCE:
Porosity is one of the major important property of the soil as it
facilitates the storage of water availability of air within the soil.
Porosity also affects the structure and consistency of the soil.
It helps the plant roots to grow further move easily within the
soil environment.
Porosity is a main indicator of soil structural quality. Therefore,
its characterization is essential for assessing the impact of
adding organic matter to a soil system.
22. Soil consistence is defined as a term to designate the
manifestation of physical forces of cohesion and adhesion
acting within the various level of moisture content.
It is the physical condition of the soil at various moisture content
as evidenced by the behavior of that soil toward mechanical
stresses or manipulation.
The manifestation as stated in the definition includes as follows:
i. Behavior of the soil towards gravity, pressure, thrust and pull.
ii. Tendency of the soil mass to adhere to foreign bodies.
iii. Tactile quality of soil on rubbing between the fingers.
23. SOIL TILLAGE:
Tillage is the physical manipulation of soil with tools and
implements to result in good tilth for better germination of seeds
and subsequent growth of crops.
Tillage helps to replace natural vegetation with useful crop and
to improve the physical condition of soil, control of weeds,
insect-pests and diseases and also bring the nutrient available
to plant.
The cultivation is not possible without tillage operation.
24. SOIL COMPACTION:
Soil compaction is the process of increasing dry bulk density of
soil, reducing the pore space by expulsion of air through applied
pressure on a soil body. Under very high pressure, the soil
particles may themselves be compressed but only slightly.
Compaction due to the machines used for tillage of land,
harvesting and threshing of crops has adverse effects on the
growth of plants due to reduced aeration and increased bulk
density of the soil.
Compaction of the soil may also be due to grazing of animals,
human activities in the field and intense rainfall as well as
irrigation.
25. IMPORTANCE:
Soil consistence provides a means of describing the degree
and kind of cohesion and adhesion between the soil particles as
related to the resistance of the soil to deform or rupture.
Consistence is an important characteristic of the soil as affects
the nature of force between particles of the soil.
It is important for Tillage or traffic consideration.
26. Soil micro-organisms show maximum growth and activity at
optimum soil temperature range.
All crops practically slow down their growth below the
temperature of about 9°C and above the temperature of about
50°C.
The biological processes for nutrient transformations and
nutrient availability are controlled by soil temperature and soil
moisture.
27. Sources of Soil Temperature are:
1) SOLAR RADIATION:
The main source of heat is the sun. The temperature of the soil
is primarily dependent upon the amount of radiant energy
received from the sun.
The sun rays reach the earth after they pass through the
atmosphere and warms the surface of the soil on which they
fall.
A part of soil temperature is lost to the air by radiation.
28. 2) CONDUCTION:
The heat is absorbed from solar radiation by surface soil and is
conducted down the depth of the soil.
The interior of the earth is very hot, the conduction of this heat
to the soil is very slow.
3) BIOLOGICAL AND CHEMICAL REACTION:
In a soil, various biological and chemical reaction occurs. As a
result, some amount of heat is liberated in the soil due to
biological and chemical reaction.
29. IMPORTANCE:
Soil temperature is important to growers, especially for spring
planting. Many seeds need a certain minimum temperature for
germination.
Soil temperature has a profound influence on seed germination,
root and shoot growth, and nutrient uptake and crop growth.
Seeds do not germinate below or above a certain range of
temperature but micro-organism functioning in the soil is very
active while a certain range of temperature, which is about 27°
to 32°C.
30. REFERENCES & RESOURCES
WEB BASED RESOURCES:
1. Shreeja D. Soil Aeration: Physical and Biological Properties of Soil.
http://www.soilmanagementindia.com/soil-air/soil-aeration-physical-and-biological-properties-of-
soil/1730.
2. María Belén Almendro-Candel, Ignacio Gómez Lucas, Jose Navarro-Pedreño and Antonis A. Zorpas
(August 29th 2018). Physical Properties of Soils Affected by the Use of Agricultural Waste,
Agricultural Waste and Residues, https://www.intechopen.com/books/agricultural-waste-and-
residues/physical-properties-of-soils-affected-by-the-use-of-agricultural-waste.
BOOKS:
1. Brady, Niles, and Ray R. Weil. 2008. The Nature and Properties of Soil, 14th edition. Upper Saddle
River, NJ: Prentice Hall.
2. Chesworth, Ward, ed. 2008. Encyclopedia of soil science. Dordrecht, Netherlands: Springer. ISBN 1-
4020-3994-8
3. J.sehgal, Kalyaniprakashan. Physical properties of soil. Pedology Concept and Application.
