Term
| The attraction of water molecules for each other is called? |
|
Definition
|
|
Term
The attraction of water molecules for solid surfaces is called?
|
|
Definition
|
|
Term
| Which atoms of a water molecule bond with clay minerals? |
|
Definition
| the hydrogen atoms (positively charged) |
|
|
Term
| Name and describe the three forces affecting the energy level of soil water. |
|
Definition
1. matric force: caused by adhesion of water molecules to particle surfaces
2. osmotic force: the affinity of water to ions and other solutes, and
3. gravity, which always pulls water towards the Earth's center |
|
|
Term
| What determines the direction and rate of water movement in soils and plants? |
|
Definition
| The difference in energy level of water from one site or one condition to another |
|
|
Term
Which soil water has a greater energy level?
Water in saturated soils, or water in dry soil. |
|
Definition
| Water in saturated soils (think about how free they are to move around) |
|
|
Term
| The difference in energy levels between pure water (at a standard pressure and temperature) and that of soil water is termed? |
|
Definition
|
|
Term
| Differences in water potential of two soil samples reflect differences in their absolute energy levels. This means that water will move from a soil zone having a ____ soil water potential to a _____ soil water potential. |
|
Definition
|
|
Term
| Total soil water potential (Ψt) is a function of? |
|
Definition
the sum of:
gravitational potential (Ψg)
matric (Ψm) or submergence potential (Ψs)
osmotic potential (Ψo) |
|
|
Term
| gravitational potential Ψg = |
|
Definition
= gh
that portion of the total soil water potential due to differences in elevation of the reference pool of pure water and that of the soil water; usually positive (since the soil water elevation is usually higher than the reference pool) |
|
|
Term
|
Definition
the portion of the total soil water potential due to the attractive forces between water and soil solids as represented through adsorption and capillarity; always negative
|
|
|
Term
|
Definition
| the portion of the total soil water potential due to the presence of solutes in the soil water; will generally be negative |
|
|
Term
Give examples for when the potential energy of soil water (i.e., the difference between the free energy in the soil and pure water at a reference state). . .
. . .is positive?
. . . is negative? |
|
Definition
Positive: the soil water is at a higher elevation than the standard (gravitational potential)
Negative: the soil water has a greater number of salts or other solutes (osmotic potential); or the soil water is attracted by soil solids (matric potential) |
|
|
Term
| Matric potential is the result of _____ forces. It is always ________. |
|
Definition
|
|
Term
| What potential is responsible for the movement of water horizontally across a soil matrix? |
|
Definition
|
|
Term
| In the presence of a osmotic potential gradient, ____ moves in response to differences in osmotic potential only if a semipermeable membrane exists between the differing zones. If no membrane is present, the ______ moves to equalize concentrations. |
|
Definition
|
|
Term
| The matric potential is always ______. The submergence potential is always _________. |
|
Definition
|
|
Term
| Because soil zones are not generally separated by semipermeable membranes, the ______ potential has little effect on the mass movement of water in soils. |
|
Definition
|
|
Term
| Do soils with high soluble salts have higher or lower osmotic potential (Ψo)? |
|
Definition
|
|
Term
| Osmotic potential in roots must be ______ in order for the plant to uptake water. |
|
Definition
|
|
Term
| A water release characteristic curve or water characteristic curve shows soil water content (θ) as a function of __________. |
|
Definition
soil water potential
pg 184 (Brady and Weil) |
|
|
Term
| In a water release characteristic curve, typically, soil water content increases as soil water potential _________. |
|
Definition
| increases (i.e., becomes less negative) |
|
|
Term
| The phenomena that the relationship between soil water content and potential, determined as the soil dries is different that when it is rewetted is known as a ___________ ? |
|
Definition
|
|
Term
| What two mechanisms are responsible for this hysteresis in the soil? |
|
Definition
1. the nonuniformity of soil pores
2. the shrinking/swelling of clay minerals |
|
|
Term
| Define volumetric water content (θ). |
|
Definition
| (θ) = the volume of water in a given volume of dry soil |
|
|
Term
| Define mass water content (θm) |
|
Definition
| θm = the mass of water associated with a given mass of dry soil |
|
|
Term
| There are seven methods to measure soil water content (volumetric, mass). Name as many as you can. |
|
Definition
1. gravimetric - destructive sampling, slow
2. resistance blocks - can be automated
3. neutron scattering - radiation permit needed, expensive, not accurate in high organic soils
4. time domain reflectrometry - can be automatedexpensive
5. tensiometer - accurate to 0.1 to 1 kPa, limited range, inexpensive,
|
|
|
Term
| submergence potential Ψsub |
|
Definition
a result from hydrostatic pressures
(think pressure on your eardrums when you dive into a pool)
|
|
|
Term
| The presence of solutes (inorganic salts or organic compounds) ______ the potential energy of water, primarily because of the reduced freedom of movement of the water molecules that cluster around each solute ion or molecule |
|
Definition
|
|
Term
In what situations does each apply?
Ψg -
Ψsub -
Ψm –
Ψo –
|
|
Definition
Ψg - when there is a difference in elevation between the reference pool of pure water and the soil water
Ψsub - when soil water is saturated
Ψm – when soil water is not saturated
Ψo – when there is a difference in the solutes (inorganic salts or organic compounds) between the reference pool of pure water and the soil water
|
|
|
Term
| What are the two pressure potentials? |
|
Definition
| submergence potential and matric potential |
|
|
Term
| Define submergence potential Ψs |
|
Definition
|
|
