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SSC 109 > Midterm 2 > Flashcards

Midterm 2 Flashcards

1
Q

What are the conceptual divisions of soil OM?

A

Labile, Stabilized, and Recalcitrant pools of OM

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2
Q

What is the added N interaction and how does it affect the mineralization of N from crop residues and SOM?

A

About only 40% of N fertilizer actually goes to the crop. The rest goes to microbial biomass and is immobilized.

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3
Q

How is biological fixation costly ?

A
  1. The reaction can be wasteful with H2 being lost (source of acidity) 2. the reaction is very costly for the reduction of dinitrogen to ammonia
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4
Q

What are 5 types of plant available forms of N?

A
  1. Symbiotic biological fixation 2. Free-living biological fixation 3. Nox (lightening) 4. Fertilizers 5. Other (geological, pollution, wildfire
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5
Q

What is the Haber-Bosch process and what is the issue with it?

A

Industrial N2 fixation to NH3. Only 4% of reactive N enters the human mouth, the rest is lost into air, soil, surface water, and groundwater.

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6
Q

Name 2 inorganic reduced N foms

A

NH3 and NH4+

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7
Q

Name 3 inorganic oxidized forms of N

A

Nox, N2O, NO3-

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8
Q

What are 3 examples of organic N

A

urea, amino acids, proteins

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9
Q

Where is most of the global N residing?

A

in the atmosphere - 78%

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10
Q

Plants contain ____ % N by weight

A

1-6 %

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11
Q

There is ____ N in the top 1-ft of cultivated soils

A

0.03 - 0.4%

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12
Q

95% of N is in (inorganic/organic) form

A

organic, unavailable to plants

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13
Q

True or False: NO2- is not important to plants

A

False but it is less common. Found in feed lots.

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14
Q

Name the substrate and end product of nitrification

A

NH3 (substrate) –> NO3-

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15
Q

What can be lost during both nitrification and denitrification?

A

N2O

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16
Q

Why is more N2O lost from nitrifier denitrification (urea) than in (NH4)2SO4 soil?

A

the pH and NH4 concentration is greater

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17
Q

When soils are waterlogged, microbes get O2 from ___ and ____.

A

NO2- and NO3-
When conditions are aerobic, microbes must use a different electron acceptor

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18
Q

Does Asymbiotic or Symbiotic fix more N ?

A

Symbiotic

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19
Q

True or False: It is useful to do a soil test for N

A

False. Not very useful but does give some correlation to total N information

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20
Q

What two nutrients limit N fixation?

A

P and Mo as they can affect photosynthesis

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21
Q

Name the substrate and end product of denitrification

A

NO3 (substrate)- —> N2

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22
Q

True or False: NO and NO3- are toxic to microbes

A

True

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23
Q

Plants absorb N as _____ & ____

A

NO3- and NH4+

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24
Q

Do plants have a high tolerance for NH4+?

A

No - it can retard growth and restrict K+ uptake. Grasses have higher tolerance.

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25
Q

How does high NO3- uptake affect pH?

A

it will increase pH (more alkaline) which will increase cation absorption.

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26
Q

How does high NH4+ uptake affect pH?

A

it will decrease pH (more acidic) which will increase anion absorption. This can impact growth.

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27
Q

What are 3 functions of N in plants?

A
  1. assimilated into amino acids/proteins 2. part of nucleic acid 3. part of chlorophyll
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28
Q

What is a symptom of excess N in plants?

A

delayed crop maturity, weak due to not enough C in cell wall

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29
Q

What are examples of organisms involved in biological N fixation?

A

Rhizobium, Actinomycetes, Blue-green Algae, Frankia

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30
Q

What 4 factors affect N2 fixation? Why?

A

soil pH (acidic soils), nutrient status, photosynthesis, and climate. All of these factors can inhibit rhizobial activity/growth

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31
Q

What are the two steps in N mineralization?

A

step 1 aminization and step 2 ammonification

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32
Q

What is synchrony in relation to N in soil and in plants?

A

N mineralization needs to correspond to crop N uptake. If synchrony is off, leaching can occur.

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33
Q

What is the fate of ammonium (NH4+)? 5 examples

A
  1. can be converted to NO2- and No3- in nitrification 2. can be taken up by plants 3. can be utilized by bacteria for decomposition (immobilization) 4. can be fixed to clay minerals 5. can be converted to NH3 and slowly released via volatilization
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34
Q

What 6 factors affect nitrification?

A
  1. supply of NH4+ 2. population of nitrifying organisms 3. soil pH (optimum at pH 8) 4. soil aeration 5. soil moisture 6. soil temp
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35
Q

Why does denitrification occur?

A

NO3 is toxic to microbes. Also, In anaerobic environments, microbes will obtain O2 from NO2- and NO3-.

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36
Q

What 8 factors affect denitrification?

A
  1. decomposable OM 2. soil water content 3. aeration 4. soil pH 5. temperature 6. NO3- level 7. presence of plants 8. NO2- level
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37
Q

Where might NH4 get fixed in clays? What can bump it off ?

A

NH4+ can be fixed in the interlayer of 2:1 clay minerals. Example is illite. K+ fertilization can kick out ammonium as it has the same hydrated radius size

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38
Q

What is the most commonly used inorganic N source?

A

Anhydrous ammonia (NH3). Urea is the most common dry N as it behaves similar after hydrolization.

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39
Q

Is N mobile or immobile in plants?

A

mobile

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40
Q

Mobility of N in soil

A

NH4+ is immobile but NO3- is mobile

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41
Q

Deficiency symptoms of N in plants

A

chlorosis or necrosis in older leaves. Symptoms begin at the leaf tip and proceed along the midrib

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42
Q

What are the functions of P in plants?

A

P is a component of nucleic acids, ATP, NADP, and phospholipids. P is also a cofactor of some enzymes

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43
Q

What are deficiency symptoms of P in plants?

A
  1. stunted growth 2. dull green leaves. purple leaves and stem starting at the tip/edge of leaf 3. older leaves show symptoms first
44
Q

P forms absorbed by plants

A

P is found in the form of phosphates (PO4) which is a stable form. H2PO4- and HPO4^2- are dominant and are absorbed by plants.

45
Q

How is P commonly lost in the soil?

A

erosion as P is concentrated near surface soil in the organic form

46
Q

What pH is optimum for PO4 availability ?

A

pH 6.5

47
Q

In pH <6.5 PO4 is not available because

A

PO4 is adsorbed to Fe-Al oxides and clays

48
Q

In pH >6.5 PO4 is not available because

A

PO4 binds to Ca

49
Q

Why will 1:1 clay impact P retention more than 2:1

A

Because of the broken edge effect

50
Q

True or False: Monovalent cations adsorb more P than divalent cations on the CEC

A

False

51
Q

How can you make P more available in the soil?

A

Flooding, base saturation, add fertilizer, add manure, add SOM

52
Q

Mobility of P in plants vs. soil

A

P is mobile in plants but little/no mobility in soils

53
Q

What is the most important P source (fertilizer)

A

Acid treatment P fertilizers that make rock phosphate more available. There are two types a. single superphosphate b. triple superphosphate

54
Q

Forms of inorganic P in soil

A

Calcium phosphates, Iron & Aluminum phosphates, H2PO4-, HPO4^2-

55
Q

What soils is Olsen-P test used for?

A

P test for alkaline and calcareous soils

56
Q

What soils are Bray 1 or Mehlich 3 tests used for?

A

P test for acidic and neutral soils

57
Q

Where does most of S come from?

A

volcanoes

58
Q

What form(s) of S do plants uptake?

A

primarily SO4^2-. leaves can take up SO2

59
Q

Plants contain __% S

A

0.1 - 0.5

60
Q

In plants, S content increases in
[place these in order: Cruciferae, Gramineae, Leguminosae]

A

Gramineae<Leguminosae<Cruciferae

61
Q

Where is 90% of S in plants found?

A

Amino acids

62
Q

If a plant is experiencing S deficiency, what nutrient will they show an increase in?

A

non-protein N in the form of NH2 or NO3-

63
Q

Give 3 examples of what S is important for in plants

A
  1. protein structure 2. synthesis of coenzyme A 3. synthesis of chlorophyll
64
Q

____ppm of SO4^2- is adequate for most plants

A

3-5 ppm

65
Q

What are 6 forms (non specific) of S found in soil?

A
  1. Solution SO4^2- 2. Adsorbed SO4^2- 3. SO4^2-Co- precipitation 4. Silicate minerals 5. primary minerals 6. reduced inorganic S (S^2- and S^0)
66
Q

What depth is S found in soil?

A

Greater depth subsoils due to presence of Fe/Al oxides and clay

67
Q

What are 5 sources of mineralizable S?

A
  1. Humus 2. plant residues 3. microbial byproducts 4. mineralization closely related to C content 5. organic S in soils
68
Q

Mineralization of S is (fast/slow).

A

slow, making it difficult to measure for prediction

69
Q

What extractants would you use to pull S off sites?

A

Phosphate ions as they have a greater strength of adsorption

70
Q

S is (mobile/immobile) in plants

A

mobile

71
Q

2 symptoms of S deficiency

A

chlorosis in upper leaves and reduced plant growth

72
Q

True or False: S is mobile in all soil tyles

A

False, immobile in very acidic soils

73
Q

How to increase S in soil?

A

Add manure, ammonium sulfate, gypsum, magnesium sulfate, potassium sulfate

74
Q

Form of Ca absorbed by plants and is it mobile?

A

Ca2+, immobile in the plant

75
Q

True or False: Ca deficiencies are very common

A

False

76
Q

Where would you expect to find Ca deficiencies?

A

highly leached and unlimed acidic soils

77
Q

Ca in plants is ____%

A

0.2 - 1%

78
Q

What 4 things is Ca important for the plant?

A
  1. structure and permeability of cell wells 2. uptake of NO3- 3. Regulation of cation uptake (K+ and Na+) 4. elongation and cell division
79
Q

Ca in soil is ____ ppm

A

8 - 45 ppm

80
Q

What type of soils have high Ca and why?

A

Arid soils due to low rainfall = less leaching (Calcite CaCO3)

81
Q

The amount of Ca2+ available to plants depends on what 5 things?

A
  1. soil pH (acidity will impede on Ca uptake) 2. low Ca2+ binding CEC 3. Clay type 4. Other cations being taken up instead 5. leaching of Ca making it not available
82
Q

Name 6 Ca fertilizer sources

A
  1. single- and triple-superphosphate 2. CaEDTA 3. Phosphate rocks 4. Animal and municipal OM 5. Liming material 6. Egg shells
83
Q

Ca is (immobile/mobile) in soils

A

immobile

84
Q

What happens to Ca2+ in pH > 6.5?

A

precipitates as Ca-phosphate minerals

85
Q

Plant symptoms of Ca2+ deficiency

A

stunted growth due to poor development of terminal buds and root tips. Necrosis of upper leaves

86
Q

What form of Mg is absorbed by plants and is it mobile?

A

Mg2+, mobile

87
Q

True or False: Plants take up less Mg compared to Ca and K

A

True

88
Q

There is ____% of Mg in plants

A

0.1 - 0.4%

89
Q

What 3 things is Mg important for the plant?

A
  1. Chlorophyll 2. Protein formation 3. phosphate transfer in ATP reactions
90
Q

What is grass tetany?

A

An Mg deficiency in cattle when they consume forages low in Mg.

91
Q

What other cations may depress Mg in plant tissues?

A

NH4+ and K+

92
Q

Mg in soil is ____ ppm

A

5 - 50

93
Q

What can you apply to low-Mg acidic soils?

A

Dolomite

94
Q

What are the most commonly used Mg dry fertilizers (common name)

A

epsom salts (magnesium sulfate)

95
Q

Plant Mg deficiency symptoms

A

Interveinal chlorosis, necrosis, general withered appearance

96
Q

Mg is (mobile/immobile) in soil

A

mobile

97
Q

What happens to Mg in pH >7.2?

A

Mg availability decreases

98
Q

What happens to Mg in very acidic soils?

A

low exchangeable Mg

99
Q

True or false: addition of cations increases Mg uptake

A

False, reduces

100
Q

What enzyme is responsible for N fixation?

A

Nitrogenase

101
Q

Name: NH4

A

ammonium

102
Q

Name: NH3

A

ammonia

103
Q

Name: N2O

A

nitrous oxide

104
Q

Name: N2

A

dinitrogen

105
Q

Name: NO2-

A

nitrite

106
Q

Name: NO3-

A

nitrate

107
Q

Name: SO4^2-

A

sulfate

SSC 109 (2 decks)

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