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soil hyraulic conductivity Flashcards

1
Q

how much water is in the earths soils? (total water percent)

A 
soils = 0.001 (0.05 % of fresh water) 
groundwater = 1.7
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2
Q

how can you manage soil water in 4 ways in preparation for drought and climate change?

A
  1. breed drought-tolerant crops
  2. conservation agriculture
  3. hydrological seasonal forecasting
  4. understanding soil water characteristics
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3
Q

what are 3 aspects of conservation agriculture

A
  1. no till to preserve structure
  2. constant ground cover
  3. diverse crops adn pasture to increase OM
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4
Q

how does soil structure effect water conservation

A

better sturcture will lead to increase infiltration and soil moisture.
degraded structure will lead to more runoff and soil will be less effective at storing water

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5
Q

what are the two ways soils water is expressed and what are their units?

A
  1. gravimetrically (wetness w g/g)

2. volumetrically/porosity (θ m3/m3 and dimensionless)

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6
Q

calculation for gravimeteric water content

A

w = Mass liquid/mass soil

* 100 for percent

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7
Q

Calculation for volumetric water content

A

θ = voume liquid (=mass liquid)/volume soil

*100 for percent

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8
Q

calculation for θ using wetness

A

w * bulk density (p)

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9
Q

converting mm to volume (ML)

A

100 mm/ha = 1 ML/ha

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10
Q

4 methods to measure water content (field or lab)

A
  1. bulk density cores
  2. sensors (probes)
  3. permanent feild equipment
  4. satellite soil mositure (active or passive measure temp ) only surface of the soil
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11
Q

3 statuses of the water in soil

A
  1. saturation
  2. field capacity
  3. wilting point
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12
Q

what is saturation

A

all pores are filled with water not all water is available

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13
Q

what is field capacity

A

~2 days after saturation, gravoty drains excess water from pores and some water is held

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14
Q

what is wilting point

A

water is held very tighly by soil and it is not available to plants (too much energy to absorb)

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15
Q

what 2 factors describes the state of water in soils

A

the water content (quantity volume %)
in relation to the water potential (quality) (wettest possible condition of the soil related to texture and bulk density
eg 20%water is high quality for sand and low quality for clay

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16
Q

which soil sandy, loam, clay has the most available water

A

aggregated loam. clay can hold more water however most in unavailable because it is held tightly to particles

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17
Q

where does water flow in relation to potential

A

high potential to low potential eg a wet sand to a dry sand.

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18
Q

what are the 2 reducing forces of soil water (output)

A
  1. evaporation

2. gravity (drainage)

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19
Q

what are the 2 holding forces of water

A
  1. adsorption (surrounding particles)

2. capillarity (in pores)

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20
Q

what are the 2 forces that drive capillarity

A
  1. adhesive

2. cohesive

21
Q

what are adhesive forces

A

attraction of water molecules to solid surfaces (attraction of dissimilar substances). at low moisture content forms a thin layer

22
Q

what are cohesive forces and when does this occur

A

water molecules pulling each other together, this can move water upwards. mostly at high water content

23
Q

what is the water potential at saturation (J/kg)

A

0 J/kg (positve)

most soils are less than this (negative)

24
Q

what are the 3 pathways water flows (high to low potential)

A
  1. precipitation (downwards + gravity)
  2. evaporation (upwards)
  3. Plant uptake (lateral/upwards)
25
Q

how do plants uptake water

A

this is not due to an exertion of energy by the plants rather a different in potential. the lowest potential is in the top leaves (eg -1000 kPa) compared to high potential at roots (eg -10 kPa)

26
Q

what units describe water potential (3 ways)

A
  1. energy per mass (j/kg)
  2. energy per volume (kPa)
  3. pressure head (m)

1 j/kg = 1 kPa = 0.1m

27
Q

what is the simple capillary model

A

height in cm (the smaller the capillary the higher the water)
the height of the water is inversly proportional to the radius of the capilary

28
Q

what is the capillary rise formula

A

height cm = 0.15/radius capillary cm

29
Q

what is the capillary fringe

A

the space between the saturated zone (ground water) to the unsaturated zone intermediate zone/soil zone

30
Q

what causes capillary rise to become an issue (eg AUS)

A

groundwater is high in salinity. when native vegetation is removed and either left bare or replaced with shallow crops the groudwater level becomes higher and capillary forces increase salinity in the soil.

31
Q

what is a non wetting sand and wetting sand

A

hydrophobic soil, water that sits ontop of soil with >90 degree contact angle. in comparison to wetting sand angle = 0

32
Q

what causes non wetting sands

A

coating of sand particles with fungi (microbes) gums and waxes. caused by vegetation high in lipids (issue in SA and WA)

33
Q

how does clay fix non wetting sands

A

high surface area of clay means substance cannot coat all particles

34
Q

what is another way you can fix non wetting sands

A

using wetting agents such as detergents to increase surface area

35
Q

what is the main issue with non wetting soils

A

soils will not equally moisten therefore cannot crop

36
Q

what is a duplex soil and what can be done to fix hydropobic topsoil

A

soil profile marked by distinct textures (texture contrast) sandy topsoil with clay subsoil. these can be mixed by devling and spading

37
Q

what is the water retention curve/soil moisture characteristic curve

A

representation between volume of water and potential of water. the morre negative the value (potential) the drier the soil eg 0 = saturated

38
Q

how to interpret the water retention curve

A

the lower the potential (eg -10000) the smaller the pore size.

the higher the potential (eg -1) the larger the pore size

the most pores iswhere the graph is the flattest, if the graph is steep there is even distribution of pores

39
Q

what is field capacity

A

(-10 kpa, 1m) water in soil after saturated flow drained (pores smaller than 30mm diameter

40
Q

what is permanent wilting point

A

-1500 pka, 150m

planst cannot exert enough energy to absorb water

41
Q

what is available water capacity

A

field capacity - wilting point = AWC throughout whole depth of soil (mmwater/mmsoil)

42
Q

how do you get the height of water using AWC

A

AWC X thickness of soil

43
Q

height of water (using AWC mm) values rating

A

<100 small

>200 large

44
Q

what is Plant available water capacity

A

AWC mm of all layers up until root depth eg add AWC of all layers until that thickness

45
Q

what is the equivilant of feild capacity

A

drained upper limit (DUL)

46
Q

what is the equivilant of permanent wiling point

A

Crop lower limit (CLL)

47
Q

when do you irrigate

A

halfway between PWP and FC

48
Q

AWC ratings (m3/m3)

A

<0.1 small

>0.2 large

SS (10 decks)

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