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Soils > Mid Term 2 > Flashcards

Mid Term 2 Flashcards

1
Q

Soil water functions

A

Essential for photosynthesis
Turgor pressure
Transports nutrients
Helps plant for temperature variations

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2
Q

What is hydrogen bonding

A

Weak interactions between the partial positive charge of hydrogen and with the partial negative charge of oxygen

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3
Q

What is cohesion

A

Sticking of water molecules to each other from hydrogen bonding. Responsible for surface tension

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4
Q

What is adhesion

A

Sticking of water molecules to other molecules

Enables water to “climb” up soil pores - capillary action

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5
Q

Forms of water in soil and what they are

A

Hygroscopic Water - films around clay particles, only form of water found in air dried condition

Capillary water - held on capillary pores (<1mm thick), main form of available water

Free water - drainage or free draining water found in the bigger pores and moves downward by gravity

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6
Q

Definition of field capacity

A

All macro pores have drained, only micro pores are filled. Plants can access this water

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7
Q

Definition of permanent wilting point

A

Any water still in soil is not available, plant wilts and dies

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8
Q

Infiltration definition

A

A measure of the rate at which rain fall or irrigation is absorbed into the soil (in/hr, mm/hr)

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9
Q

What are water movements through soil (4)

A

Gravitational flow

Matric flow

Capillary rise

Osmotic potential

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10
Q

What is gravitational flow

A

Movement of water through saturated soil

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11
Q

What Is matric flow

A

Movement of water through unsaturated soil ( wet to dry)

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12
Q

What is capillary rise

A

Water is pulled upward from water table in micropores by cohesive/adhesive forces

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13
Q

What is Osmotic potential

A

Determined by concentration of solutes in soil water (water flows from zones of low solutes to zones of high solutes) important for root-water interaction

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14
Q

Why is water movement important

A

Soil with rapid internal drainage have higher risk of leaching
Helps determine best drainage plan
Understanding how salinity works

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15
Q

Chemical properties of soil (5)

A 
Anion-Cation exchange capacity 
Reaction (pH)
Calcium carbonate content
Salinity and solicits
Soil organic matter
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16
Q

Cation exchange capacity

A

The total number of exchangeable cations a soil can hold

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17
Q

Anion exchange capacity

A

Relative amount of negatively charged anions which can be held by a given weight of soil

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18
Q

What is soil pH

A

Soil pH is a measure of acidity or alkalinity of soil
Seldom go beyond 4-9
Soils become acidic as rainfall leaches away basic cations such as (Ca, Mg, K, Na) while Al and H stay behind making the soil acidic
More rain = more acidic

19
Q

Other factors that affect soil pH

A 
Type of vegetation 
Type of parent material
Amount +type of OM
Amendments
Salinity and sodicity
20
Q

Why are saline and sodic soils alkaline

A

Not a lot of water movement through soil that causes leaching so basic cations stay in soil making it basic

21
Q

Why do we use lime

A 
Reduces Al and other metal toxicities
Improves physical condition of soil
Stimulates microbial activity
Increases CEC in variable charge soils
Increases availability of several nutrients
Supplies Ca and Mg to plants
Improves symbiotic N fixation in legumes
Improve crop yields
22
Q

How does salinity happen

A

Occurs when groundwater containing salt is able to reach the root zone or soil surface where it evaporates and leaves an accumulation of salt

23
Q

Conditions required to create a soil salinity problem

A
  1. Soluble salts in subsoil, ground water or both
  2. High water tables to carry soluble salts into root zone by capillary action (<6 ft from surface)
  3. Plants susceptible to soil salinity (pulses, vegetables, oilseeds)
24
Q

Salinization is a natural process controlled by

A

Hydrology
Geology
Biological processes

25
Q

What is regional or artesian discharge salinity

A

Occurs when water within an underlying aquifer is under sufficient pressure to reach land surface. Then water evaporates at surface and salts are left behind

26
Q

What is side hill seep salinity

A

Occurs where permeable glacial drift overlies impermeable materials such as clay or bedrock
Lateral movements eventually intersects a side hill surface
Groundwater discharges at this point and evaporation of water leave behind salt at surface

27
Q

What is bathtub or evaporitic ring salinity

A

Occurs adjacent to wet depressions or sloughs
Lateral upward capillary flow from the water table concentrates salts adjacent to the slough, leaving salt in a concentric ring surrounding the slough

28
Q

How do we test for salinity

A

Electrical conductivity-a measure of soluble salts within the soil
2 methods used to measure EC
1. Saturated paste method

  1. Soil:Water ratio method
29
Q

Managing primary salinity

A

Strategic cropping choices to manage water

Reduce tillage

Increase soil OM

30
Q

Managing secondary salinity

A

Strategic cropping choices to manage water

Drainage strategies to manage water and leach salts out of soil profile

31
Q

Sodic soils

A

Characterized by: elevated sodium concentration relative to calcium and magnesium
pH usually above 8.5
May be able to manage with gypsum addition

32
Q

Components of soil

A

45% mineral
25% water
25% air
5% OM

33
Q

Components of OM

A

33-50% decomposing OM
33-50% stabilized OM
<10% fresh residue
<5% living organisms

34
Q

What is OM

A

Generally considered to be plant residue in various stages of decomposition in the soil and…
Microflora-bacteria, fungi
Microfauna-Protozoa and nematodes
Macrofauna-earthworms and millipedes

35
Q

What is decomposed residue called in OM

A

Humus

Responsible for dark colour in Ah horizon

36
Q

How is humus determined

A

By measuring the amount of organic carbon in the soil

37
Q

What happens when the C:N ratio is high

A

Immobilization of soil nitrogen

38
Q

What happens when the C:N ratio is low

A

New mineralization of nitrogen

39
Q

What is C:N ratio

A 
Carbon to nitrogen
C:N of plant residue depends on crop type 
100:1 wide ratio
15:1 narrow ratio
>25:1 net mobilization 
<25:1 net mineralization
40
Q 
C:N ratio numbers
Cereal crop
Legume residue
Soil humus
Microbes
A

Cereal 80:1
Legume 25:1
Soil humus 10:1
Microbes 6:1

41
Q

Starting soil conditions

A

Modest levels of nitrate
Low c/n ratio
Low microbial activity

42
Q

What happens when you return heavy amounts of cereal crop residue

A

Can cause a temporary shortage of mineral nitrogen for crops (why we burn residue in fields)

43
Q

Removal of crop residue why

A

Common on heavy clay soils where cool wet conditions slow decomposition
Removal means loss of vital nutrients such as nitrogen and phosphorus will be lost

44
Q

Factors affecting soil OM levels (7)

A
  1. Natural vegetation
  2. Temperature
  3. Soil moisture
  4. Soil texture
  5. Aeration
  6. Cropping and cultivation
  7. Landscape position

Soils (1 decks)

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