Soil water movement and plant available water

Question 1

3 types of water low

Answer 1

1. saturated flow
2. unsaturated flow
3. vapor flow

Question 2

Saturated flow

Answer 2

• all pores filled with water
• gravity is the driving force (hydraulic gradient)
• can occur both vertically and horizonally

Question 3

Saturated flow occurs

Answer 3

After a rain fall, in poorly drained soil, when there is a restrictive layer

Question 4

Darcys law

Answer 4

Governing equation that dictates flow in saturated conditions
J=Q/t=AKsat Change in water potetial/l

J= the flux of saturated flow
A= the cross section area
L= length of column
Ksat= hydraulic conductivity

Question 5

Saturated Hydraulic conductivity

Answer 5

the ease with which pores of a saturated soil transmit water

Question 6

More _____, higher Ksat greater rate of saturated flow

Answer 6

Macropores

Question 7

Which soil texture will typically have the highest Ksat

Answer 7

Sand

Question 8

Why does no till areas have higher hydraulic conductivity

Answer 8

More micropores and aggregate stability

Question 9

Preferential flow

Answer 9

Water and its constituents moving by preferred pathways through a ports medium
flows through large micropores to ground water unrestricted

Question 10

Unsaturated flow

Answer 10

Occurs when soils are not saturated
(large pores filled with water)

Question 11

____ forces drives the movement of water in unsaturated conditions

Answer 11

Matric

Question 12

External water vapor movement

Answer 12

movement from the soil surface to air

Question 13

Internal water vapor movements

Answer 13

Movement between soil pores

Question 14

Driving force

Answer 14

Vapor moves from areas of high pressure to areas of low vapor pressure

Question 15

Infiltration

Answer 15

process by which water enters a soils pore space

Question 16

percolation

Answer 16

process by which water moves through pore space

Question 17

Infiltability

Answer 17

Rate at which water can enter the soil at the surface

Question 18

Infiltrability equation

Answer 18

Ask professor

Question 19

Infiltrability is ____ ______ over time

Answer 19

not constant

Question 20

Infiltrability when soil is s shrinking clay

Answer 20

Infiltrability will be very high then sharply decline after pore swell

Question 21

Percolation factors

Answer 21

can be both saturated

Question 22

Wetting front

Answer 22

steep hydraulic gradient and forms a sharp boundary between wet and dry soil

Question 23

Perched water tables

Answer 23

accumulation of groundwater that is above the water table in the unsaturated zone (above an impermeable layer)

Question 24

What creates a perched water table on a slope?

Answer 24

springs or seeps

Question 25

Why does perched water table occur above sand?

Answer 25

?? ask professor

Question 26

Maximum retentive capacity (saturation)

Answer 26

All water pores are saturated Zero water potential 0 kPa

Question 27

Field capacity

Answer 27

Max amount of water soil can hold that is useful to plants Little downward movement micropores filled with air -10 to -30 kPa

Question 28

Permanent wilting point

Answer 28

Plants can no longer supply water Water still in smallest pores soil appears dusty -1500 kPa

Question 29

Hygroscopic water

Answer 29

water remaining in soil after soil has dried beyond wilting point

Question 30

Available water holding capacity (AWHC)

Answer 30

Water that is held between field capacity and permeant wilting point

Question 31

Factors affecting the amount of plant available ater

Answer 31

-matric potential -osmotic potential -soil depth and layering

Question 32

Highest water holding capacity

Answer 32

Fine sandy loams, silt loams, silty clay loams

Question 33

How do plants obtain water from soil

Answer 33

- Capillary movement of water to roots - root extension into moist soil

Question 34

Capillary movement of water to roots

Answer 34

- water uptake by roots creates areas of lower potential around root surfaces - totally movement is usually a max of a few cm -important during dry periods when root density is high

Question 35

Limitation of root extension

Answer 35

small proportion of soil comes into contanct with roots

Question 36

Layers that restrict roots

Answer 36

-bedrock -compacted or dense zones - plow pan - Frangipani or dense glacial till -cemented zones - Abrupt change in texture

Question 37

root depths

Answer 37

- very shallow <25 cm - shallow 25-50 cm - moderately deep 50-100 cm - deep 100-150 cm - very deep > 150 cm