GROUP II
2. Soil Properties
Influencing Water
Relations
1.Physical Properties
2.Biological Properties
3.Chemical Properties
I. Physical Properties
Physical properties are the most
visible and can be observed without
using equipment like scanners or
microscopes. They are reflective of the
solid soil particles such as sand, silt
and clay and the manner in which they
are arranged. They can be used to
define and classify soil types and
horizons. In addition, they are very
effective for field/lab
demonstrations.
II. Biological Properties
Biological Properties represent
the direct and indirect influence
of the living organisms habituating
a particular soil. Soil biological
properties reflect how well-suited
a soil is to support life. Most of
the properties require specialized
and high powered equipment for
observations or measurements.
III. Chemical Properties
Chemical properties represent
the complex chemical reactions and
processes occurring in the soils.
They represent nutrient
availability, deficiency, toxicity,
salinity and sodicity just to name
a few. Almost all of the properties
require field equipment or lab
analysis for measurement.
2.1 Soil Profile
The soil profile is a
vertical section of the soil
that depicts all of its
horizons. The soil profile
extends from the soil surface
to the parent rock material.
Horizons
O: The O horizon is a surface horizon
that is comprised of organic material
at various stages of decomposition.
A: The A horizon is a surface horizon
that largely consists of minerals
(sand, silt, and clay) and with
appreciable amounts of organic matter.
E: The E horizon is a subsurface horizon
that has been heavily leached. Leaching
is the process in which soluble
nutrients are lost from the soil due to
precipitation or irrigation.
B: The B horizon is a subsurface horizon
that has accumulated from the layer(s)
above. It is a site of deposition of
certain minerals that have leached from
the layer(s) above.
C: The C horizon is a subsurface
horizon. It is the least weathered
horizon. Also known as the saprolite, it
is unconsolidated, loose parent
material.
2.2 Soil Depth
Soil depth defines the root
space and the volume of soil
from where the plants fulfill
their water and nutrient
demands. Soil depth can greatly
influence the types of plants
that can grow in them. Deeper
soils generally can provide
more water and nutrients to
plants than more shallow soils.
2.3 Particle Size
Composition of Soil
Soil is the thin layer of
material covering the earth's
surface and is formed from the
weathering of rocks. It is made up
mainly of mineral particles,
organic materials, air, water and
living organisms—all of which
interact slowly yet constantly.
• Soil particles vary greatly in size, and
soil scientists classify soil particles
into sand, silt, and clay.
• The size of soil particles is important.
The amount of open space between the
particles influences how easily water moves
through a soil and how much water the soil
will hold.
• clay particles are smaller than 0.002 mm in
diameter.
• Silt particles are from 0.002 to 0.05 mm in
diameter
• Sand ranges from 0.05 to 2.0 mm.
• Particles larger than 2.0 mm are called
gravel or stones.
2.4 Soil Texture
Soil texture refers to the size
of the particles that make up the
soil and depends on the proportion
of sand, silt and clay-sized
particles and organic matter in the
soil. The texture of a
soil determines soil characteristics
that affect plant growth. Three of
these characteristics are waterholding capacity, permeability, and
soil workability.
2.5 Soil Structure
In geotechnical engineering, soil
structure describes the arrangement
of the solid parts of the soil and of
the pore space located between them.
It is determined by how individual
soil granules clump, bind together,
and aggregate, resulting in the
arrangement of soil pores between
them.
Soil structure is the
arrangement of soil particles into
small clumps, called peds or
aggregates. Soil particles (sand,
silt, clay and even organic matter)
bind together to form peds.
Structure correlates to the pore
space in the soil which influences
root growth and air and water
movement.
2. 6 Soil Consistence
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. Soil consistency
refers to the resistance of soil to
mechanical stress or manipulation at
various moisture contents. Soil
consistency is determined for wet,
moist and dry soil samples.
2.7 Bulk Density and
Particle Density
Particle density—is the density of
solid soil particles only, i.e.,
measurement does not include pore space
(air space), the average value is 2.65 g
cm−3.
Bulk density—is the density of a
volume of soil as it exists naturally, it
includes air space, organic matter, and
soil solids.
2.8 Pore Space
Pores are microscopic spaces
between particles of rock or sand.
Pores are actually where oil and
natural gas occur. Once those minerals
are produced, the pores remain empty.
Played out oilfields are an excellent
bank of safe, empty pore space.
The pore space of soil contains the
liquid and gas phases of soil, i.e.,
everything but the solid phase that
contains mainly minerals of varying
sizes as well as organic compounds.
Pore Types
Macropore
The pores that are too large to have any
significant capillary force.
Mesopore
The largest pores filled with water at field
capacity. Also known as storage pores because
of the ability to store water useful to
plants.
Micropore
These are "pores that are sufficiently small
that water within these pores is considered
immobile, but available for plant extraction.
Thank You
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