Fundamental
Concepts
Of Soil-Water
System

CONTENTS
Absorption of water
Plant water
status
Water movement in
Soil
✓Entry of water
✓Soil pores
✓Soil water
✓Field capacity
✓Permanent
wilting
Fundamental
concepts
01
02
03
04
✓Soil texture
& Structure
✓Gravityaction
✓Capillaryaction
✓Sandy & clayey soil
✓Active transport
✓Passive transport
✓Plant water
status
✓Plant water
potential

Fundamental concepts of Soil-Water System
✧ Entry of water into Soil
Water enters into soil by process
of Infiltration and further
movement of water in soil occurs
by process of Percolation
✧ Infiltration
In this process water is absorbed
in the soil mass (upper layer of
the earth crust) to meet the soil
moisture deficiency.
Infiltration
Precipitation
evapo-transpiration

Fundamental concepts of Soil-Water System
✓ After meeting the soil
moisture deficiency if any
excess water is available, it
will move vertically
downward and meet the
G.W.T.(ground water table),
this vertical downward
movement is called as
percolation.
Percolation
Percolation
Precipitation
Infiltration
Soil water seepage
evapo-transpiration
To deep
ground
water
To stream
stream

Soil Pores
Two types of pores in soil.
✧Macropores
Large soil pores, water does not
retain in them due to their larges
sizes, air particles entrapped in
them.
✧Micropores
Small soil pores, hold water against
the force of gravity. Only water
entrapped there is used by the plants
by capillary action.
Macropores
Micropores

Carbon
Cycle
Types of water
✧Gravitational water
Form of water, which reaches at the soil water table due
to the gravitational force after the rainfall. This form is
not available to plants.
✧Hygroscopic water
Thin film of water is tightly held by the soil particles is
called hygroscopic water. This water is also not
available to the plants.
✧Capillary water
Water exists between soil particles in small capillary
pores is called Capillary water. It is the most common
available form of water for absorption.
Gravitational
Hygroscopic
Capillary

Field capacity & permanent wilting
✧ Field capacity:
“Field capacity is the amount of soil moisture or
water content held in the soil after excess water
has drained away”
At field capacity the soil is wet and contains all
the water it can hold against gravity.
✧ Permanent wilting point:
At the “Permanent Wilting Point” (PWP) the soil
is dry and the plant can no longer extract any
more water from soil.
Wilting point
Field capacity
Unavailable water
Available water

Water movement in soil
✧ Water movement in the soil is strongly influenced by soil texture and soil
structure.
✧ Water moves more quickly through the large open macropores found on sandy
soils than the smaller pores of silt or much smaller micropores in dense clay soils.
✧ Gravity is the dominant force that moves water downward while capillary action
is the major force for movement of water in any direction i.e., upward, and lateral
water movement.
✧ Water movement in sandy soil is mostly through gravitational water movement
because of their large pore spaces.
✧ Clayey soils on the other hand have many micropores, hold more water than
sand.

✓ “Plant water status reflects the plants response to soil-water supply
and atmospheric demand driven by water.”
✓ Water potential determines the direction of the flow of water in any
system. i.e. water moves from high water potential to low water
potential.
✓ The water potential helps to understand how the movement of water
takes place into the root and within the plants.
Plant water potential
Plant water status

In higher plants water
is absorbed through
root hairs which are
in contact with soil
water.
Two mechanisms of
water absorption in
plants:
Absorption of water in plant systems
(1)
Active
Absorption
(2)
Passive
Absorption
Osmotic
Absorption
Non osmotic
Absorption

✓ Root cells play active role in the absorption of water and metabolic
energy released through respiration is consumed.
Active absorption may be of two kinds:
✓ When water is absorbed from the soil into the xylem of the roots
according to the osmotic gradient.
✓ When water is absorbed against the osmotic gradient.
Active Absorption of water
Osmotic absorption of water
Non osmotic absorption

✓ It is mainly due to transpiration, the root cells
do not play active role and remain passive.
✓ During absorption of water by roots, the flow
of water from epidermis to endodermis may take
place through three different pathways:
(i) Apoplastic pathway (cell walls and
intercellular spaces),
(ii) Trans-membrane pathway (by crossing the
plasma membranes) and
(iii) Symplast pathway (through
plasmodesmata).
Passive absorption of water
Apoplast pathway
Symplast pathway
Vacuole Cytoplasm Cell
wall
Plasmodesmata

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