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Soils > Unit 4, 5 > Flashcards

Unit 4, 5 Flashcards

1
Q

What is nitrification?

A

the process performed by soil bacteria that turns ammonium into nitrate

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2
Q

Why is the symbiotic relationship between rhyzobia bacteria and root beneficial?

A

nitrogen fixation - nitrogen is converted to ammonia by the rhyzobia bacteria, then the nitrifying bacteria turns the ammonia into nitrate

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3
Q

What is the soil organism associated with roots of some plants that has been effective at cleaning up pipeline spills?

A

mycorrhizal

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4
Q

What component (fraction) of SOM promotes formation of large aggregates that show water aggregate stability?

A

active

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5
Q

What is the best description of humus?

A
  • dark in color very resistant to microbial decomposition
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6
Q

Properties of humus that are similar to clay?

A
  • negative charges
  • form aggregates
  • colloidal nature
  • high specific surface area
  • large water holding capacity
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7
Q

What is a benefit of clay and humus forming a strong interaction?

A
  • helps form aggregates
  • humus is protected from decomposition
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8
Q

Which combination of climate and soil aeration results in highest accumulation of SOM?

A
  • cold temps
  • waterlogged conditions
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9
Q

What is the difference between active and stable SOM?

A
  • active: non-humic, most important food source for microbes, quickly decomposed
  • stable: humus, dark colour, strongly attached to soil mineral particles, does NOT decompose easily
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10
Q

What is more affected by management practices, active or stable SOM?

A

active

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11
Q

What is SOM?

A
  • complex and diverse mixture of organic substances
  • all organic substances contain organic carbon (from photosynthesis)
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12
Q

The 3 major components of SOM?

A
  • living biomass
  • active
  • stable
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13
Q

What are the main groups of soil microorganisms?

A
  • bacteria and fungi
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14
Q

What is the topsoil (0-15cm) biological activity dominated by?

A
  • earthworms & microorganisms
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15
Q

How many microorganisms can be found in a teaspoon of healthy soil?

A

15 million to 4 billion

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16
Q

What are benefits of soil microorganisms?

A

SOM decomposition
- mineralization: nutrients change from organic to mineral ionic form
- production of organic glue
- formation of by-products used for humus synthesis
- nitrification
- nitrogen fixation
- phosphorus plant uptake
- mycoremediation
- plant growth enhancement
- phytoremediation
- humus synthesis

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17
Q

What is mineralization?

A

SOM decomp
nutrients changing from organic to mineral ionic form

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18
Q

How is organic glue formed and how is it helpful?

A
  • produced by soil microorganisms decomposing the SOM. as they eat the SOM it produces glue
    -sugar like product that binds soil particles into larger water stable aggregates
  • promotes aggregate formation and stability
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19
Q

What is nitrification?

A

Nitrosomonas and nitrobacter
bacteria oxidizes ammonium to nitrate
NH4+ + 2O2 → H2O + 2H+ + NO3

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20
Q

What is nitrogen fixation?

A
  • rhizobia bacteria associated with legume roots are the most important nitrogen fixing microorganisms
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21
Q

What is a symbiotic relationship?

A

mutually beneficial

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22
Q

What is phosphorus uptake?

A

Mycorrhizae (fungus)-root
symbiotic association increases plant P uptake

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23
Q

What is mycoremediation?

A

Mycorrihizae fungi from dandelion roots are inoculated into straw mats and rolled out into crude oil contaminated sites to break down the hydrocarbons

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24
Q

What is humus synthesis?

A
  • microbes link decomposed by-products into complex compounds called humus making them resistant to further decomp
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25
Q

What is carbon to nitrogen ratio?

A

The higher the C/N ratio of a plant residue the slower its decomposition - not enough nitrogen
to satisfy microorganisms’ growth

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26
Q

What are aerobic microbes?

A

need oxygen for metabolism

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27
Q

What are anaerobic microbes?

A

use powerful compounds such as NO3 and may produce N2O (greenhouse gas)

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28
Q

What is the ideal temp for microbe growth?

A

20-40C

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29
Q

What is the most important food source for microbes?

A

active SOM (non-humic)

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30
Q

Does hummus decompose easily?

A

no, can stay in soil for centuries or even millennia

31
Q

Which type of SOM is colloidal in nature?

A

stable (Humus)

32
Q

Is SOM the only factor that forms water stable aggregates?

A

yes

33
Q

Soil property benefits of SOM?

A
  • improves consistence
  • increase porosity
  • improve drainage (fine soils)
  • improve water holding capacity (medium soils)
  • decrease bulk density
  • reduces / prevents erosion
  • ## improve fertility
34
Q

Environmental benefits of SOM?

A
  • less water needed
  • less fertilizer
  • reduced water pollution
  • greater plant production
  • carbon sink / storage
35
Q

Which factors result in high SOM accumulation?

A
  • low temp
  • low aeration
36
Q

Which texture of soil has the highest accumulation of SOM?

A

clayey soils

37
Q

Why does more SOM stay in chernozemic cultivated soils vs luvisolic forested cultivated soils?

A
  • forested soils are more acidic so the OM doesn’t decay as quickly
38
Q

Which practices reduce loss / increase SOM?

A
  • no till
  • no summer fallow
  • varied crop rotation
  • addition of animal manure
  • cover crops
39
Q

What is the importance of cation exchange process in soils?

A
  • allows soil to both store and supply nutrients
  • reduce leaching losses
40
Q

Why are forested soils more acidic than grassland soils, in general?

A

forested vegetation is more acidic

41
Q

Which of the following ions are non-acidic (base cations)?

A

Ca, Mg, K, Na

42
Q

Is every alkaline soil saline?

A

no

43
Q

What is the main cause of poor plant growth in saline soils?

A

difficulty of water uptake

44
Q

What is the main cause of soil salinity in the prairies?

A

movement of excess saline groundwater to the soil surface

45
Q

What is capillary rise?

A

salinized groundwater to come to the surface

46
Q

What are common salt tolerant weeds in southern AB?

A

koshia, foxtail barley

47
Q

Solonetzic is the name for which types of soil in canada?

A

saline-sodic

48
Q

What is active acidity?

A
  • concentration of H+ in soil solution
  • a pH test will only measure active acidity
49
Q

What is reserve acidity?

A
  • -H+ adsorbed on clay and humus colloids
  • much larger than active acidity
50
Q

What is an exchange of cations?

A

when one adsorbed cation diffuses into the soil another moves into its place, adsorbed cations are held by weak forces

51
Q

What is CEC?

A

cation exchange capacity
total sum of exchangeable cations adsorbed or loosely held by soil colloids

52
Q

Is CEC an indicator for soil fertility?

A

yes

53
Q

What is percent base saturation?

A

a formula used in diagnosing chernozemic A horizon

54
Q

How are CEC units expressed?

A

cmol(+)/kg (centimol of positive charges per kg of soil)

55
Q

What is a common type of clay in semi-arid climates?

A

smectites (80-120 cmol/kg)

56
Q

Which soil textures have higher CEC?

A

clay, humus

57
Q

What is buffering capacity?

A

the soils capacity to maintain a relatively stable pH despite the presence of acidifying or alkalizing factors

58
Q

Would soils with high CEC need more lime or less lime to correct pH?

A

more lime to correct pH

59
Q

Does sand have a high or low buffering capacity?

A

low

60
Q

Acids produce which ion when dissolved in water?

A

hydrogen H+

61
Q

Bases produce which ion when dissolved in water?

A

hydroxide OH-

62
Q

What is pH?

A
  • measurement of the concentration of H+ ions in a solution
  • measures the soil reaction
63
Q

In pure water OH- is equal to H+, which means a pH of?

A

7

64
Q

An increase in H+ ions would mean that the solution pH increases or decreases?

A

decreases. it becomes more acidic with more H+ ions

65
Q

More hydrogen = more acidic

A
66
Q

What is the pH range for luvisolic soils?

A

about 4-6
contains pyrite

67
Q

What is the pH range for productive agricultural soils?

A

5.5 - 8

68
Q

What is considered a neutral pH in soil terms?

A

6.5 - 7.5

69
Q

Why are soils with a pH below 5.5 a concern?

A
  • increase in Mn, Fe, Al
  • reduces nitrogen, Ca, Mg, K, P
  • reduces soil bacteria
70
Q

What happens to phosphorus when soil is too acidic?

A

P bonds tightly to Al, Mn and Fe and is removed from soil solution

71
Q

Which ion is highly toxic to plants?

A

aluminum

72
Q

Which metal micronutrients are essential to plants but too much becomes toxic?

A

Mn, Fe

73
Q

How is aluminum (pg 24)

A
74
Q

What is hydrolysis?

A

when H and O split from H2O

Soils (3 decks)

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