Soil profile and soil physical properties anand corrected
1. Soil Profile
It is vertical section of the soil through all its horizons and
extending up to parent material
Soil morphology
A study of the horizons in a soil profile and their sequesnce, depth
and soil properties
Soil horizon
A horizontal layer of soil parallel to the soil surface and differ fro
adjacent layer
Master horizon
The five master horizons designated as O,A,E,B ,C
By Dr. AB Jadhav, SSAC, AC, Pune
4. O horizon
‘O’ stands for organic matter/dark colour
It is called as organic horizon / may have 20 to 30 % OM
It forms above the mineral soil
Developed from plant and animal residues
Generally present in forest area and absent in mineral soil
Oi- Less decomposed material
Oe- Medium decomposed material
Oa – Highly decomposed
5. ‘A’ horizon
Present in surface soil
It is called topmost mineral soil
Contains decomposed organic matter
Dark in colour
soil particles in this zone are smaller and finer compared to the lower
horizons of the soil.
This layer where seeds germinate and roots grow
Organisms, like earthworms, fungi, and bacteria, are mainly
concentrated in this layer. As most of the biological activities take place
in this layer, it is often referred to as the ‘biomantle’.
6. ‘E’ horizon
Zone of eluviation
It is called leaching horizon
Silicate clay., FE and Al oxides leach out from this horizon
Light in colour
Contains resistant mineral like quartz
Poor in mineral and clay content
The E horizon in rarely seen in a cultivated area where it is mixed
with the A horizon because of plowing activity.
7. ‘B’ horizon (Sub soil)
Zone of illuviation
It is present in subsoil
Called accumulation horizon
Dark in colour
B horizon is rich in clay and minerals like iron or aluminum
In this horizon accumulate or deposited by CaCO3, FE and Al oxides
Plant roots may reach this layer
8. ‘C’ horizon (Sub soil)
Deposited by unconsolidated parent material
Formed below solum
This horizon is outside the zone of biological activities
May or may not be same as parent material
As plant roots do not reach this layer, the C horizon is typically
devoid of organic matter.
9. ‘R’ horizon (Sub soil)
Its bed rock underlying consolidated material
10. Pedon: The smallest volume that can be called ‘soil’. It is three
dimensional, it extends downward to depth of plant root. Its lateral
cross section is roughly hexagonal. It range from 1 to 10 m2 in size
depending on the variability of the horizon
• Pedon: Includes vertical & lateral extent of soil
• Profile: Include vertical extent of soil
Epipedon: A diagnostic surface horizon that includes upper part of the
soil that is darkened by organic matter
Endopedon: Diagnostic horizonz found in subsurface
Polypedon: Two or more continuous pedon commonly refereed to as a
soil individual
14. O Horizon
The letter ‘O’ stands for organic, which implies that this horizon is rich
in humus, i.e., the organic matter of plant and animal origin. This
organic matter, which is usually in various stages of decomposition,
gives this horizon its characteristic dark color. In order to be identified
as the O horizon, the layer has to have more than 20-30 percent organic
matter. Furthermore, depending on whether the origin of the
decomposed matter is visible to the naked eye or not, the layer is
divided into two zones – O1 and O2.
A Horizon (Topsoil)
The A horizon is the topmost layer of the mineral soil. As it lies just
below the O horizon, this layer also has some amount of humus in it and
therefore, it is darker than the layers below. Similarly, the soil particles
in this zone are smaller and finer compared to the lower horizons of the
soil. It is this layer where seeds germinate and roots grow. Even the soil
organisms, like earthworms, fungi, and bacteria, are mainly
concentrated in this layer. As most of the biological activities take place
in this layer, it is often referred to as the ‘biomantle’.
15. E Horizon
The E horizon, which lies between the A and B horizons, is known by its
characteristic light color, and its sand and silt content. It is poor in
mineral and clay content as these are lost to the lower layers in the
process of leaching and therefore, it is also called the layer of eluviation
(leaching). The soil particles of this layer are larger in size than those in
the A horizon, but smaller than those in the underlying B horizon. The E
horizon in rarely seen in a cultivated area where it is mixed with the A
horizon because of plowing activity.
B Horizon (Subsoil)
The B horizon is rich in clay and minerals like iron or aluminum. It is
usually reddish or brown in color, which can be attributed to the
presence of the iron oxide and clay. Though this layer has a high mineral
content as compared to the topsoil, the chances of some organic matter
reaching this layer as a result of the leaching process cannot be ruled
out. Plant roots may reach this layer, but the chances of this are pretty
less, and therefore, its humus content is very low.
16. C Horizon
The C horizon is mainly made of large rocks or lumps of partially
broken bedrock. It is considered the transition layer between soil
and parent material. This layer is least affected by weathering as
it lies deep within the soil and is inaccessible to the soil-forming
agents. That explains why the rocks in this layer haven’t
changed much since their origin. As plant roots do not reach this
layer, the C horizon is typically devoid of organic matter.
R Horizon (Bedrock)
The R horizon is basically the deepest soil horizon in the soil
profile. Unlike the horizon above, this horizon does not comprise
rocks or boulders, but instead is made of continuous mass of
bedrock. It is very difficult to dig through this layer. In some
regions, the bedrock is located just a few inches below the
surface, and in some, it is found several feet below.
18. Soil Texture :-
Soil texture refers to the relative proportion of sand, silt, clay.
The soil separates are expressed in terms of diameter in mm
of the particles.
The size of particles in soil is not subject to ready change.
Thus it is considered as a permanent feature and a basic
property of soil.
Mechanical analysis of soil separates i.e. the proportion of
sand, silt, clay is done by Bouyoucos hydrometric method.
19. CLASSIFICATION ACCORDING TO ISSS
SYSTEM
SR.
NO.
SOIL
SEPARATES
DIAMETER
(mm)
1
Coarse sand 2.0-0.2
2
Fine sand 0.2-0.02
3
Silt 0.02-0.002
4
Clay <0.002
Reference :- text book of fundamental of
soil science. ( Mali & Patil )
20. CLASSIFICATION ACCORDING TO USDA SYSTEM
SR.
NO.
SOIL SEPARATES DIAMETER
(mm)
1
Very coarse sand 2.0-1.0
2
coarse sand 1.0-0.5
3
Medium sand 0.5-0.25
4
Fine sand 0.25-0.10
5
Very fine sand 0.10-0.05
6
silt 0.05-0.002
7
Clay <0.002
21. Reference :- Text book of
fundamental of soil science
( Mali & Patil )
Textural triangle diagram according to ISSS
system of classification of soil particles
22. Importance of soil texture :-
To asses value of land.
Suitability of land to raise different crop
Governs nutrient holding and nutrient supplying ability of soil.
Evaluate the amount of amendment needed for soil reclamation.
Determine the pore spaces and distribution of micro and macro
pores.
23. Soil Structure
The arrangement and organization of primary and secondary
particles in a soil known as soil structure.
Types of structure :-
i. Plate like:
The aggregates are arranged in horizontal plates.
Horizontal axis is more develop than vertical.
When the plates are thick – platy, thin – laminar.
24. ii. Prism like :
The vertical axis is more developed than horizontal giving
a pillar shape. Length 1-10 cm.
When the tops are rounded - columnar.
When flat/plane and clear cut - prismatic.
25. iii. Block like:
All the dimensions are about the same size.
when the faces are flat and distinct and the edges are
sharp angular - angular blocky.
when the faces and the edges are mainly rounded -sub angular
blocky.
26. iv. Spheroidal:-
All rounded aggregates are placed in this category.
The aggregates of this group are usually termed as granular
which are relatively less porous.
When the granules are very porous – crumb.
27. Factors Affecting soil structure
Climate
Organic matter
Tillage
Plant roots and residues
Animals and microbes
Fertilizers
Wetting and Drying
Water
Inorganic cements- CaCo3
Clay
28. Density of soil
Particle density Bulk density
Bulk Density
• Soil bulk density is defined as the oven dry weight of soil
per unit of its bulk volume.
29. Particle Density
The weight per unit volume of solid portion of soil is called
Particle Density.
It is also called as True density.
The particle density of normal soil is 2.65 g/cc.
Particle density is higher if larger amount of heavy minerals
are present in soil.
With increase in inorganic matter the soil particle density
increases.
It is determined by Pycnometer method.
30. Bulk Density
The oven dry weight of soil per unit of its bulk volume is
called Bulk density.
It is also called as False Density and it is dynamic property
of soil.
The bulk density of the normal soil is 1.25 to 1.33 g/cc.
Bulk density is always smaller than particle density.
Addition of bulky organic manures decreases Bulk Density
thereby increases porosity, air exchange, microbial activity
which ultimately improves health of soil.
Clay soil has lower bulk density while sandy soil has higher.
It is determined by Clod Coating method.
31. Bulk density Particle density
B.D. = Wt. of oven dry soil/bulk
volume (Solid + Pore space)
P.D.= Wt of oven dry soil/ volume
of solid
Also called apparent density Also called true density
BD is smaller than particle density Higher
Particle size increases, bulk density
also increase
e.g. Clay -1.1 g cm3 while sandy –
1.6 g cm3
Particle size increases…particle
density decrease
Sand- 2.6 and clay-2.83 g cm3
It is dynamic property It is stable property
It is determined by clod coating
method
It is determined by pycnometer
It is varies from 1.1 to 1.7 g C3
Pore space will not affect the bulk
density
Pore space will not affect the
particle density
32. Soil porosity
(Refers to percentage of pore space)
Soil porosity refers to that part of soil volume that is occupied
by air not and by soil particles.
The amount of pore space in soil determined by arrangement of
particles of sand, silt and clay.
In sandy soil the pore space is high and in clay soil pore space is
low.
Macro pores are high in sandy while Microspores in clay
Presence of organic matter increases the pore space.
With increase in particle density, the porosity is decreased.
33. Porosity = (1 – BD/PD) X 100
BD- Bulk density of soil
PD-Particle density
For Example
BD is 1.25 g/cm3 and PD is 2.65 g/cm3
(1-1.25/2.65) X100
(1-0.47 ) X 100= 0.53 X 100 =
53 % is porosity
34. Soil colour
Soil colour is due to either mineral matter or organic matter
and mostly both.
White colour indicates the dominance of silica or presence of
soluble salts.
Red colour indicates the accumulation of iron oxide.
Brown and Black indicates the level and type of organic matter.
Soil colour directly influences soil temperature.
35. Measurement of soil colour
Soil colour is measured using Munsell colour chart and
expressed in terms of Hue, value and chroma.
Hue – Dominant spectral colour dominant spectral
colour. (0 (less red) to 10 (more yellow))
Value - Intensity of colour. Relative light of colour as
compared to absolute white (Black – 0 and white 10)
Chroma - Purity of colour. Relative purity or strength
of the spectral colour. e,g, Dark grey or black brown
36. Black colour of soil Organic matter
Dark gray colour Due to Na, Ca bass and organic matter
Red colour Due to iron oxide
White colour Due to silica and lime
Brown colour Organic matter and iron oxide
5YR 5/6
5YR= hue
5 = Value
6 = Chroa
38. Soil consistency
It refers to the resistance of soil materials to
deformation or rupture.
It depends upon the degree and kind of forces which
attract one molecule to another.
It varies with size, shape and arrangement of soil
particles and colloids.
39. Soil Temperature
Soil temperature is measured by using Soil
thermometer at various depth like 10cm, 15cm.
Soil temperature affect other soil properties as well the
plant growth.
It is influenced by the soil colour.
Temperature Affects nutrient and water movement.
40. Effect of Soil Temperature on Soil and Plant Growth
Microbes activity-
Lowest activity when soil temp. is below 50 C and above 540 C.
Optimum temp. for microbe activity is 25-35 0C.
Absorption of soil water
Physical properties of Soil
Plant Disease
Nutrient availability
Seed germination and plant growth
Soil formation
