Topic 3: Soil Water

Question 1

SMAP

Answer 1

soil moisture active passive

Question 2

Phreatic Zone

Answer 2

zone of saturation (realm of groundwater )

Question 3

water table

Answer 3

maximum height of groundwater , level which below ground is saturated with water

Question 4

capillary fringe

Answer 4

subsurface layer in which groundwater seeps up from a water table by capillary action to fill pores

Question 5

Vadose Zone

Answer 5

unsaturated zone, realm of soil moisture

Question 6

what is the structure of soil?

Answer 6

45% mineral particles
25% air
25% water
5% organic matter
*water and organic content can vary

Question 7

properties of clay

Answer 7

highly weathered particles
mostly clay minerals
adsorbs soil water very effectively

Question 8

adsorption

Answer 8

water in surface layer stuck through electromagnetic forces

Question 9

properties of sand/silt

Answer 9

less weathered particles
less reactive/charged
retain less soil water
larger pores, higher hydraulic conductivity

Question 10

less total pore volume= more or less porosity?

Answer 10

less porosity

Question 11

list some soil properties

Answer 11

• • grain size and type
• -sorting
• -bulk density
• -water content, degree of saturation
• -hydraulic conductivity
• -thermal state

Question 12

main components of soil by mass

Answer 12

solid and water mass ((Mm and Mw)

Question 13

main components of soil by volume

Answer 13

mineral, water and air (Vm, Vw, Va)

Question 14

what is volumetric water content

Answer 14

fraction of water in soil, amount of pore space filled with water. at saturation Va=0

Question 15

adsorbed/hygroscopic water vs. capillary water vs. gravitational water

Answer 15

capillary is least tightly held between grains, hygroscopic is right around the soil particle and is the most tightly held. gravitational water is the air or space otherwise impacted by gravity.

Question 16

what is field capacity

Answer 16

water in soil that can be retained against gravity from adsorbed water and capillary pressure

Question 17

what is permanent wilting point

Answer 17

is the water content at which plants cannot draw water out of the soil

Question 18

what is available water

Answer 18

water that is available to plants

Question 19

what is gravimetric water content?

Answer 19

is the mass fraction of water in the soil

Question 20

what is gravitational water?

Answer 20

water in a soil that is freely available for gravitational drainage (free water in pore space)

Question 21

divisions of the subsurface P water vs P atmos

Answer 21

Vadose Zone: PwP atmos

Question 22

what is surface tension

Answer 22

is a function of the interaction between the two materials at the interface

Question 23

does suction increase or decrease with increased pore size?

Answer 23

decreases with larger pore diameter

Question 24

what is suction a function of?

Answer 24

moisture content and where it is wetting/drying

Question 25

which pores fill first ? when drying, which pores empty first?

Answer 25

wetting: small pores fill first so water increases slowly
drying: large pores empty first, rapid decline in water

Question 26

hydraulic conductivity at high vs low water contents

Answer 26

high water contents: coarse soils have a higher hydraulic conductivity than fine soils
low water contents: fine soils have a higher hydraulic conductivity than course soils

Question 27

how do plant stake up water from the soil?

Answer 27

through osmosis

Question 28

how much soil water is used for photosynthesis vs waste

Answer 28

1-2% for photosynthesis and tissue growth, 98% waste

Question 29

how is excess water evacuated from a plant

Answer 29

opening of the stomata, occurs during the day, downfall is only a 1:600 ratio of CO2 to H2O

Question 30

does water move faster or slower in saturated soil?

Answer 30

it moves faster- 1-10cm/hr vs. unsaturated at 1mm/hr

Question 31

forces that draw water up

Answer 31

osmotic pump pulling water into plant roots (overnight)

evapotranspiration (daytime)