soil water storage and movement

Question 1

what is soils role in water storage

Answer 1

-temporary reservoir for all types of moister reaching the earth’s surface

Question 2

what would happen if the soil had no water storage capability

Answer 2

then precipitation entering the soil profile would just move down due to gravity. it would only stop when it reaches an impermeable layer if the water table

Question 3

the soils ability to hold water is affected by

Answer 3

• the unique chemical structure of water
• the negatively charged characteristics of clay and organic matter give the soil the ability to store water
• the combined influences of two forces, adhesion and cohesion

Question 4

what is adhesion

Answer 4

• the attraction of water molecules to the surface of soil particles (the + side of a water molec is attracted to the -charged surface of soil particles)
• only important over short distances

Question 5

what is cohesion

Answer 5

• the force of attraction of like molecules
• cohesion in water is the result of its dipole character: the negative side of one water molec is attracted to the positive side of another water molec

Question 6

what is field capacity

Answer 6

it is the maximum amount of water that soil can hold against the force of gravity.

when the soil reaches field capacity the majority of its pore system (possibly except for some macropores) is filled with water

Question 7

what is the saturation of a field

Answer 7

a soil reaches a point of saturation when additional water fills the remaining pore spaces, leaving no air in the pore system.

water moves throughout the soil by the force of gravity

Question 8

what is permanent welting point

Answer 8

when really dry the amount of air-filled pore space increases and remaining water films become thinner and are held with greater forces.

if drying continues the force that holds the remaining water becomes so strong that plants can no longer make use of that water

this soil moisture content is called permanent wilting point

Question 9

what is the plant available water

Answer 9

the difference between the water present at field capacity and the water remaining when the crop is unable to extract more (ie. field capacity-permanent welting point)

it is the amount of soil moisture that plants can access for growth

the amount of plant-available water depends on soil texture

Question 10

why are sandy soils more difficult to saturate

Answer 10

because their pore system is dominated by macropores that tend to drain rapidly

Question 11

why do clay soils saturate more easily

Answer 11

because of the dominance of slow draining micropores

Question 12

what are the two ways water moves through soil

Answer 12

• gravitational or saturated flow

- capillary or unsaturated flow

Question 13

what is gravitational or saturated flow

Answer 13

the rapid movement of water in larger soil pores (macropores) caused by the force of gravity

Question 14

what is capillary or unsaturated flow

Answer 14

slow water movement produced by the natural attraction of water molecules to soil particles (the combined effect of adhesive and cohesive forces). this movement is restricted to smaller soil pore systems (micropores)

the water remaining in the pore is held with a force stronger than gravity

flow can occur in any direction

Question 15

when does gravitational flow occur

Answer 15

when water infiltrates into macropores that are open to the surface

soil moisture content exceeds field capacity

soil possesses macropores 1 mm or greater

Question 16

when does saturated flow occur

Answer 16

it will only occur if sufficient water is applied to maintain a saturated soil condition.

when water application reduces or stops macropores drain rapidly causing moisture content to fall below field capacity and saturated flow stops

Question 17

what are some factors that water flow depends on

Answer 17

pore size and distribution,
pore configuration,
soil structure,
biological influence,