Factors affecting water availability in soil include soil type, porosity, and water holding capacity. Water moves through the soil via gravity, adhesion to soil particles, and cohesion to other water molecules. The amount of available water in the soil depends on the field capacity and permanent wilting point of the soil. Plant water stress can be indicated by measuring soil water potential, leaf conductance, and leaf water potential. Overexploitation of water resources and deforestation are reducing water availability in Pakistan.

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3. Factors Affecting WaterFactors Affecting Water
Availability In SoilAvailability In Soil
Topic:Topic:

4. ContentsContents
• Classification Of Soil Water
• Movement Of Water In Soil
• Soil Water Availability To Plants
• Indicators Of Plant Water Stress
• Development Of Plant Water Deficiency
• Water Availability Factors
• Water Availability In Pakistan
• Conclusion
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5. Water
• Makes up approximately 90% of a plant's
mass and performs many functions:
1. Required for seed germination
2. Carries minerals into and through the
plant.
3. Transports photosynthates and other
biochemicals
4. Cools the plant by transpiration
5. Involved in photosynthesis
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6. Classes of Soil Water
1.Gravitational water: move through gravity
2. Hygroscopic water: move in vapor form
3. Capillary water: available
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8. Movement Of Water Within SoilsMovement Of Water Within Soils
Moves along gradients
• Water in the liquid phase:
– flows through the water filled pore space
• Water in vapour phase:
–moves through the air filled pore spaces
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10. Water Movement And Retention In SoilWater Movement And Retention In Soil
Three forces are responsible for water
movement within the soil.
1- Gravity (Downward movement)
2- Adhesion (soil particles and water).
3- Cohesion (water and water).
(Adhesion+cohesion) Principal forces that
move water in an unsaturated soil.
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11. Capillary RiseCapillary Rise
 The upward movement of water.
• Responsible for the loss of water from the
soil surface by evaporation
• As soil dries, the water film surrounding
each soil particle thins. Consequently, the
adhesive and cohesive forces of attraction
increase rapidly, making it more difficult
for the plant to extract water that is held
tightly in soil particles.
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12. Soil Water Availability To PlantsSoil Water Availability To Plants
The pore spaces of soil are always filled
with water, air or a mixture of both.
 Normal condition
 Saturation condition
 Too dry condition
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13. Indicators Of Plant Water StressIndicators Of Plant Water Stress
Soil water potential
Leaf stomatal conductance
Leaf water potential
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14. Development Of Plant Water DeficiencyDevelopment Of Plant Water Deficiency
Saturated Field
Gravitational Water
Field Capacity
Plant absorption &
Evapo-Transpiration
No recharge of water:
No rain, No irrigation
Soil water deficit
Depends on
1- Rate of evapotranspiration
2- Physical & chemical properties of soil
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15. Water Availability Factors
• Available water
• (FC --- PWP)
i. FC---Saturation
ii. Below PWP
• Cohesion and adhesion forces
• Presence of salt = Plasmolysis
• Soil porosity
a) Clay soils
b) Sandy soils
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16. Water Availability Factors
• Root system
• Water table
• Hardpan
• Slope
• Saturation
• Field Capacity
• Permanent Wilting Point
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18. Water Availability Factors
• Hindrance
• Type of soil
• Water holding capacity
• Water potential
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19. Response Of Water To Different SoilsResponse Of Water To Different Soils
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20. Water holding capacityWater holding capacity
The ability of the soil to retain water is
called its water holding capacity.
• It differs from soil to soil
• Clay soils = smaller but more pores
• Sandy soils= larger but less pores
Thus, an equal volume of clay soil holds
more water than a sandy soil when the
pores are filled.
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21. Water-Holding Capacity of SoilWater-Holding Capacity of Soil
Coarse SandCoarse Sand Silty Clay LoamSilty Clay Loam
Gravitational WaterGravitational Water
Water Holding CapacityWater Holding Capacity
Available WaterAvailable Water
Unavailable WaterUnavailable Water
Dry SoilDry Soil
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22. Soil Water potentialSoil Water potential
Difference between chemical potential of pure
water to that of osomatically bound water.
 Describes
• How tightly water is bound in the soil
• Availability of water for biological processes
 Defines the flow of water in all systems
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23. Soil Water PotentialSoil Water Potential
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25. Reclamation Of SaltsReclamation Of Salts
o Leaching
o Flushing
o Scrapping
o Strip Cropping
o Soil amendments and water treatments
o Lowering soil pH
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26. Reclamation Of SaltsReclamation Of Salts
o Fertilizer management
o Irrigation management
o High transpiring plants
o Salt tolerant crops
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27. Water Availability in Pakistan IsWater Availability in Pakistan Is
Declining Rapidly!!!!!!Declining Rapidly!!!!!!
• Over exploitation of water resources
• Deforestation at the rate of 69,600 ha year-
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• Growing demand of water
• Ground water depletion at the rate of 10 m
year-1
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28. ConclusionConclusion
The soil should be carefully studied with
regard to the following:
(a) Size of soil particles
(b) Compactness
(c) Depth of water table
(d) Organic matter content
(e) Effective irrigation method
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29. • All the above aspects influence the depth
of available water that the irrigator can
store in the root zone of soil in a single
application of water and hence influence
the required frequency of watering.
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