Soil Water Flashcards
Soil Water
Properties of water that give it the ability to influence soil processes.
Water Polarity
Charges are not evenly distributed
Hydrogen Bonding
Water is attracted to itself. Responsible for Cohesion and Adhesion.
Cohesion (Surface tension)
attraction of molecules to each other (water droplets)
Adhesion
attraction of water molecules to solid surface (water drops on a window)
How do trees take up water?
Adhesion and Cohesion
Capillary Force
Due to adhesion and surface tension (cohesion), water will move upwards against the force of gravity. (thanks to soil micropores)
Do smaller pores (Sand Macropores) have more or less capillary (suction) force?
Less
Do larger pores (Clay Micropores) have more or less capillary (suction) force?
More
Water is present in soil in what 3 states? (Sponge example)
- Saturated soil-gravitational water
* Sponge full of water - Field Capacity
* Sponge not dripping but still contains water - Permanent wilting point
* Sponge is completely dry
Saturation
All pores filled with water-max water retention of a soil
Water content is equal to TOTAL porosity
Immediately after a rain or irrigation event
Water drains easily from macropores under the influence of gravitational forces
Field Capacity
The amount of water a soil can hold against the pull of gravity
Occurs when all gravitational water has drained out, typically 1 to 3 days after saturation.
Macropores are empty. Micropore are still filled with water and this is plant available water.
Permanent Wilting Point
Occurs after plants have used all plant available water
Soils that are fine textures or high in organic matter retain the greatest amount of water
Macropores
Gravitational pull is stronger than suction force so water drains freely
Micropores
Suction forces are greater than gravity so water will be pulled into micropores
Available Water Equation
Field Capacity - Permanent Wilting Point
Total Macropore Water Equation
Saturation - Field Capacity
Total Micropore Water Equation
Field Capacity - Oven Dry
Total Water Holding Capacity Equation
Saturation - Oven Dry
Can you increase water holding capacity?
Yes, with organic matter
Which soil texture is ideal for gravitational water, field capacity, AND wilting point?
Silt Loam
* Only available in surface soils in NC
Why is it bad that Clay can hold the most water?
More unavailable water because it’s holding tightly in small micropores.
Clays do not have the greatest available water holding capacity
Capillary movement takes place in which pores?
micropores
True or False: Capillary movement of water occurs due to “suction” force in ciropores
True
True or False: Capillary movement of water is possible due to the properties of cohesion and adhesion
True
What soil texture contains the greatest amount of gravitational water after a soaking rain?
Loamy sand
What is the most efficient type of irrigation?
Drip
Plant available water is held in…
Micropores
Which textural class has the greatest capacity to store TOTAL water?
Clay
Which soil texture has the greatest capacity to hold PLANT AVAILABLE water?
Silt loam
Define plant available water
soil water that is held between field capacity and permanent wilting point
Describe field capacity
a moist soil condition that occurs after the removal of all gravitational water
At field capacity, a root channel would be filled with…
air
Stormwater runoff in urban areas occurs because
concrete has an infiltration rate of zero
Which soil texture has the greatest amount of micropores?
Silty clay
What is the best option for managing urban stormwater runoff?
slow water down and promote infiltration into the soil
