PSS Exam #2 UPDATED ACTUAL Exam
Questions and CORRECT Answers
*Intro to Soil Water* - CORRECT ANSWER - ...
Where is Earth's water? - CORRECT ANSWER - -Oceans (97%)
-Atmosphere (<1%)
-Ice (2%)
-Saline lakes (<1%)
-Fresh lakes & rivers (<1%)
-Soil moisture (<1%)
-Ground water (<6%)
Why study soil water? - CORRECT ANSWER - -plant survival and growth
-loss of chemicals by leaching
-groundwater contamination
-evapotranspiration
-nutrient availability
-soil workability, consistence
-soil aeration
Soil water: - CORRECT ANSWER - -water behaves differently than water in a river or
glass
-associated with soil particles, which affects its movement; water can flow up in the soil!
Properties of water that greatly influence nature of soil water: - CORRECT ANSWER --
polarity
-hydrogen bonding
,-cohesion/adhesion
-surface tension
Polarity of water - CORRECT ANSWER - -causes attractions b/w water & other things
with charges (including water molecules!)
-Negative end (oxygen) attracted to cations (+ charged ions)
-Positive end (hydrogens) attracted to clay particles (- charged ions)
Hydrogen bonds - CORRECT ANSWER - weak bonds b/w the H of one water molecule
and the O of another
-H-bonds join a chain of water molecules
Cohesion - CORRECT ANSWER - causes water molecules to stick to each other
Adhesion (adsorption) - CORRECT ANSWER - causes water molecules to stick to other
materials (like soil particles)
Surface tension - CORRECT ANSWER - water molecules are more attracted to each other
than to the air around them--gives the water the appearance of having an elastic membrane
covering the surface
Capillary rise is due to... - CORRECT ANSWER - -adhesion to the surface and cohesion
to itself
-the height of rise is inversely proportionate to the pore/capillary radius: h=0.15/r
(finer the soil texture, the higher the capillary rise)
-In a sand, capillary rise will be fast but not high
-In a clay, capillary rise will be slow but higher than sand
-In a loam, capillary rise will be somewhere in the middle
*Capillary "rise" can take place horizontally AND vertical in a a soil
, Potential energy - CORRECT ANSWER - -key to understand movement of water through
soil (movement in soils is too slow for kinetic energy to have large influence)
-high energy status -> low energy status
-we can use this to predict movement of water through the soil
3 forces act on soil water & affect its energy: - CORRECT ANSWER - -Matric
-Osmotic
-Gravity
Matric forces - CORRECT ANSWER - -attraction of water to soil solids (same principle
that causes capillary rise in pores)
-energy of water is lower nearer to particle surfaces -- molecules have less freedom of movement
so lower energy
Osmotic forces - CORRECT ANSWER - -water is attracted to ions & solutes, which
reduces the energy state of water
-Dilute solution (high energy) -> Concentrated solution (low energy)
-Excess salts: can happen in arid environments; house plants can suffer from excess salts
-Salts in water draw water our of root tissue, killing plants
Gravity - CORRECT ANSWER - -pulls water downward
-soil water at a higher point in the profile has more energy than that at a lower point in the profile
(more energy -> less energy from surface to deeper into soil)
Hydrostatic pressure - CORRECT ANSWER - pressure exerted on soil water
Questions and CORRECT Answers
*Intro to Soil Water* - CORRECT ANSWER - ...
Where is Earth's water? - CORRECT ANSWER - -Oceans (97%)
-Atmosphere (<1%)
-Ice (2%)
-Saline lakes (<1%)
-Fresh lakes & rivers (<1%)
-Soil moisture (<1%)
-Ground water (<6%)
Why study soil water? - CORRECT ANSWER - -plant survival and growth
-loss of chemicals by leaching
-groundwater contamination
-evapotranspiration
-nutrient availability
-soil workability, consistence
-soil aeration
Soil water: - CORRECT ANSWER - -water behaves differently than water in a river or
glass
-associated with soil particles, which affects its movement; water can flow up in the soil!
Properties of water that greatly influence nature of soil water: - CORRECT ANSWER --
polarity
-hydrogen bonding
,-cohesion/adhesion
-surface tension
Polarity of water - CORRECT ANSWER - -causes attractions b/w water & other things
with charges (including water molecules!)
-Negative end (oxygen) attracted to cations (+ charged ions)
-Positive end (hydrogens) attracted to clay particles (- charged ions)
Hydrogen bonds - CORRECT ANSWER - weak bonds b/w the H of one water molecule
and the O of another
-H-bonds join a chain of water molecules
Cohesion - CORRECT ANSWER - causes water molecules to stick to each other
Adhesion (adsorption) - CORRECT ANSWER - causes water molecules to stick to other
materials (like soil particles)
Surface tension - CORRECT ANSWER - water molecules are more attracted to each other
than to the air around them--gives the water the appearance of having an elastic membrane
covering the surface
Capillary rise is due to... - CORRECT ANSWER - -adhesion to the surface and cohesion
to itself
-the height of rise is inversely proportionate to the pore/capillary radius: h=0.15/r
(finer the soil texture, the higher the capillary rise)
-In a sand, capillary rise will be fast but not high
-In a clay, capillary rise will be slow but higher than sand
-In a loam, capillary rise will be somewhere in the middle
*Capillary "rise" can take place horizontally AND vertical in a a soil
, Potential energy - CORRECT ANSWER - -key to understand movement of water through
soil (movement in soils is too slow for kinetic energy to have large influence)
-high energy status -> low energy status
-we can use this to predict movement of water through the soil
3 forces act on soil water & affect its energy: - CORRECT ANSWER - -Matric
-Osmotic
-Gravity
Matric forces - CORRECT ANSWER - -attraction of water to soil solids (same principle
that causes capillary rise in pores)
-energy of water is lower nearer to particle surfaces -- molecules have less freedom of movement
so lower energy
Osmotic forces - CORRECT ANSWER - -water is attracted to ions & solutes, which
reduces the energy state of water
-Dilute solution (high energy) -> Concentrated solution (low energy)
-Excess salts: can happen in arid environments; house plants can suffer from excess salts
-Salts in water draw water our of root tissue, killing plants
Gravity - CORRECT ANSWER - -pulls water downward
-soil water at a higher point in the profile has more energy than that at a lower point in the profile
(more energy -> less energy from surface to deeper into soil)
Hydrostatic pressure - CORRECT ANSWER - pressure exerted on soil water
