12/02/2025 12:14:58
Soils Exam 2
What is capillarity?
The movement of water in pores as a direct result of cohesion and adhesion.
What is cohesion?
The attraction of water molecules to other water molecules
What is adhesion?
The attraction of water molecules to other materials (like soil particles)
What is another term that means the same thing as adhesion?
Adsorption
What direction can capillary action move water?
Capillary action can move water in any direction
In relation to capillary fringe, what is the relationship between the height of
the rise of water to pore size?
Height of rise is inversely proportional to pore size
which soil texture has greater capillary fringe (rise), Why?
In fine textured because there are more micropores
what determines capillary fringe?
The pore size.
What are soil water potentials? What are three types?
Energy levels
1. Gravitational potential
2. Matric potential
3. Osmotic potential
What is gravitational potential?
The pull of water down in soil- percolation
What is matric potential?
The movement of water due to soil particles- adhesion, cohesion, and
capillarity at work MOVES WATER IN ANY DIRECTION
What is osmotic potential?
attraction of water molecules to ions and other solutes. reduces the energy
state of water
What is the old measure for soil water potential?
bar = 1 atmosphere of pressure
what is soil water potential?
determines the direction and rate of water movement
What are the new measures for soil water potential?
, 12/02/2025 12:14:58
Pascal (Pa) = Newtons m⁻²
Kilopascal (kPa) = 0.01 bars
Megapascal (mPa) = 10 bars
What are two methods of measuring soil water content (moisture)?
1. Volumetric water content
2. Mass water content
What is VWC?
volumetric water content ----The volume of water in a given volume of soil
What is MWC ?
Mass Water Content. The mass of water in a given mass of soil
What is the formula for determining mass water content?
MWC = (wet weight - dry weight) divided by dry weight
What is the formula for determining volumetric water content?
Db * MWC
How do you determine if soil is wet or dry based on the VWC?
Remember that soil is ~50% pore space so base the percentage determined
in the formula on how much of that space is water (i.e. if result of formula is
35% then you have a very wet soil; if 50% then you have a saturated soil
because all the pores are filled with water)
what are three types of water movement?
saturated, unsaturated and vapor
water flows in response to _______
energy gradient
What is saturated flow?
when soil pores are completely filled with water
what is vapor flow
when pressure differences develop in dry soil.
what is unsaturated flow
when large pores are filled with air
What does the rate of flow in saturated conditions depend on?
1. Hydraulic conductivity of the soil
2. Texture of the soil
3. Soil structure
4. Hydraulic gradient
When does a soil have high hydraulic conductivity? Why?
If the soil has low resistance to water movement (e.g. the pores are aligned,
relatively large, and lots of them)
Soils Exam 2
What is capillarity?
The movement of water in pores as a direct result of cohesion and adhesion.
What is cohesion?
The attraction of water molecules to other water molecules
What is adhesion?
The attraction of water molecules to other materials (like soil particles)
What is another term that means the same thing as adhesion?
Adsorption
What direction can capillary action move water?
Capillary action can move water in any direction
In relation to capillary fringe, what is the relationship between the height of
the rise of water to pore size?
Height of rise is inversely proportional to pore size
which soil texture has greater capillary fringe (rise), Why?
In fine textured because there are more micropores
what determines capillary fringe?
The pore size.
What are soil water potentials? What are three types?
Energy levels
1. Gravitational potential
2. Matric potential
3. Osmotic potential
What is gravitational potential?
The pull of water down in soil- percolation
What is matric potential?
The movement of water due to soil particles- adhesion, cohesion, and
capillarity at work MOVES WATER IN ANY DIRECTION
What is osmotic potential?
attraction of water molecules to ions and other solutes. reduces the energy
state of water
What is the old measure for soil water potential?
bar = 1 atmosphere of pressure
what is soil water potential?
determines the direction and rate of water movement
What are the new measures for soil water potential?
, 12/02/2025 12:14:58
Pascal (Pa) = Newtons m⁻²
Kilopascal (kPa) = 0.01 bars
Megapascal (mPa) = 10 bars
What are two methods of measuring soil water content (moisture)?
1. Volumetric water content
2. Mass water content
What is VWC?
volumetric water content ----The volume of water in a given volume of soil
What is MWC ?
Mass Water Content. The mass of water in a given mass of soil
What is the formula for determining mass water content?
MWC = (wet weight - dry weight) divided by dry weight
What is the formula for determining volumetric water content?
Db * MWC
How do you determine if soil is wet or dry based on the VWC?
Remember that soil is ~50% pore space so base the percentage determined
in the formula on how much of that space is water (i.e. if result of formula is
35% then you have a very wet soil; if 50% then you have a saturated soil
because all the pores are filled with water)
what are three types of water movement?
saturated, unsaturated and vapor
water flows in response to _______
energy gradient
What is saturated flow?
when soil pores are completely filled with water
what is vapor flow
when pressure differences develop in dry soil.
what is unsaturated flow
when large pores are filled with air
What does the rate of flow in saturated conditions depend on?
1. Hydraulic conductivity of the soil
2. Texture of the soil
3. Soil structure
4. Hydraulic gradient
When does a soil have high hydraulic conductivity? Why?
If the soil has low resistance to water movement (e.g. the pores are aligned,
relatively large, and lots of them)
