Exam 3

Question 1

Name the two specific reactions of mineralization.

Answer 1

• Aminization
  proteins –H2O/bacteria&fungi–>
  R-H3C2O2 (amino acids) + R-NH2 (amines) + CO(NH2)2
  PLUS CO2 + energy!
• Ammonification
  R-NH2 + H2O —>
  NH3 + R-OH + energy
  -> + H2O —> NH4+ + OH-

Question 2

What bacteria / fungi take out mineralization reactions?

Answer 2

Aminization … heterotrophic bacteria (use C for energy!)

Ammonification … aerobic / anaerobic bacteria, fungi, actinomycetes

Question 3

Define heterotrophic bacteria and give a few examples.

Answer 3

Heterotrophic bacteria cannot fix C. They use organic C for energy / growth.

Question 4

What are the two steps of nitrification?

Answer 4

#1 - Ammonia is oxidized to nitrite.
     NH3 + O2 ---> NO2- + 3H+ + 2e-

#2 - Nitrite oxidized to nitrate.
     NO2- + H2O ---> NO3- + 2H+ + 2e-

Question 5

What take out nitrification reactions?

Answer 5

Ammonia-oxidizing, then nitrite-oxidizing, soil bacterias.

Question 6

Define chemoautotrophic bacteria and give a few examples.

Answer 6

Chemoautotrophic bacteria acquires energy from the oxidation of inorganic compounds.

Question 7

What are the soil factors of nitrification?

Answer 7

• Nitrifier population (affects amt N fixed)
• Soil water content (affects rate)
• NH3 fertilization / organic manure favor nitrification due to high NH3 content
• Cold, wet soils SLOW process… therefore N losses
• Nitrification inhibitors

Question 8

When is immobilization most likely?

Answer 8

High organic matter content???

- Bacteria use NH4+ to decompose residues

Question 9

How do C:N ratios affect nitrification?

Answer 9

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Question 10

How do C:N ratios affect immobilization?

Answer 10

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Question 11

General range of C:N ratios?

Answer 11

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Question 12

When are C:N ratios high?

Answer 12

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Question 13

When are C:N ratios low?

Answer 13

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Question 14

Under what conditions will denitrification occur?

Answer 14

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Question 15

What is the pathway of denitrification, and what takes out these reactions?

Answer 15

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Question 16

Three factors of denitrification.

Answer 16

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Question 17

Discuss relative magnitude of loss from denitification as affected by drainage.

Answer 17

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Question 18

Discuss relative magnitude of loss from denitification as affected by soil organic matter.

Answer 18

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Question 19

How does volatilization occur?

Answer 19

Loss of N to atmosphere as NH3(g).

Hydrolysis of urea:
NH4+ —> NH3(g) + H+

Question 20

What is required for volatilization to occur?

Answer 20

Enzyme - UREASE … abundant in soils.

Question 21

What are factors that can cause increased ammonia volatilization?

Answer 21

• Soil pH … > 7.5 increases vol.
• Buffer capacity (CEC) … higher = stronger hold on NH4+, less vol.
• Environment … vol. increases with: increasing temp., moist soil, high pH, air movement, surface app. (1-3 peak N loss via vol.), crop residue
• N source (calcareous = ammonium vol., acid/neutral = urea)
• N placement
• Leaching
• Ammonium fixation
• Biological N-fixation
• Atmospheric N deposition

Question 22

Which N sources are worst for N loss via volatilization?

Answer 22

In calcareous soils, ammonium fertilizers.

In acid/neutral soils, urea fertilizers.

Question 23

How can we slow / stop volatilization? Discuss methods and products.

Answer 23

Avoid: surface application, urea / urea sources, liming! (lowers pH), monitor rain / temp patterns to avoid wetness / warming 1 - 3 days after application

Question 24

Which N form is prone to leaching?

Answer 24

NO3- … soluble in water, highly mobile, subject to loss to groundwater.

Question 25

Worst case scenario for nitrate leaching?

Answer 25

- Sandy soil - Over-application and / or accumulation of N - Over-irrigation and / or too much ppt - Soluble N sources

Question 26

Why do we care about nitrate leaching? Discuss issues.

Answer 26

High NO3- - N in water can be a pollutant... stimulates algae growth

Question 27

EPA limit for nitrate in drinking water?

Answer 27

10 ppm or 10 mg/L

Question 28

Which clays are most prone to fix ammonium?

Answer 28

vermiculite and mica ... in expanded lattices of clay minerals.

Question 29

Discuss free living, non-symbiotic N fixers.

Answer 29

Bacteria, common in flooded soils: - Azotobacter ... found in sugarcane vascular tissue. - Azospirillum ... association with grasses, may benefit some non-legume crops.

Question 30

What performs N fixation by legumes?

Answer 30

Bacteria (Rhizobia) in soil invade root hairs and multiply... legume roots form (pink if they're working!) nodules on surface. N2 + 16ATP + 2H+ --- nitrogenase ---> 2NH4+ + 16ADP + H2

Question 31

Typical amount of N fixed by legumes (overall)?

Answer 31

Typically 100 lbs N / A

Question 32

Typical amount of N fixed by non-symbiotic N fixers in soil?

Answer 32

Azospirillum ... ~5 lb N / A

Question 33

How much N is deposited via atmospheric deposition?

Answer 33

Less than 8 lb N / A / year

Question 34

Typical N amount in plants, per dry weight basis?

Answer 34

1 - 6% N by weight... absorbed as NO3- and NH4+

Question 35

Discuss process of reduction of nitrate to ammonium in the plant.

Answer 35

Plants metabolize NO3- to NH4+ to amino acids and proteins...

Question 36

Reduction of which is more energy intensive: nitrate or ammonium?

Answer 36

Nitrate, which is why ammonium is preferred due to evolution.

Question 37

Which tends to be more prevalent in soil: nitrate or ammonium?

Answer 37

Nitrate; however, ammonium is preferred due to evolution.

Question 38

In the plant, what must happen to nitrate?

Answer 38

Must be metabolized to NH4+

Question 39

What deals with nitrate in plants? Where does this occur?

Answer 39

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Question 40

Draw the Phosphorus Cycle!

Answer 40

Doodle time.

Question 41

Discuss forms of solution P.

Answer 41

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Question 42

Which form of P is more plant available?

Answer 42

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Question 43

Which form of P is extracted by common soil tests?

Answer 43

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Question 44

At low pH, what adsorption / precipitation forms of P are present?

Answer 44

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Question 45

At high pH, what adsorption / precipitation forms of P are present?

Answer 45

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Question 46

Discuss concept of labile P and its availability for plants and potential movement.

Answer 46

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Question 47

Discuss concept of non-labile P and its availability for plants and potential movement.

Answer 47

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Question 48

Factors of P fixation in soils.

Answer 48

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Question 49

Give examples of organic P.

Answer 49

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Question 50

At what C:N ratio does mineralization occur?

Answer 50

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Question 51

At what C:N ratio does immobilization occur?

Answer 51

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Question 52

Typically, how much P is acquired from mineralization each year?

Answer 52

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Question 53

Draw K availability figure!

Answer 53

Doodle time.

Question 54

What are the various forms of K?

Answer 54

soil solution exchangeable non-exchangeable mineral

Question 55

How does K fixation occur?

Answer 55

Weathering ... think mica / feldspars to vermiculite

Question 56

In what clay types foes K fixation occur?

Answer 56

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Question 57

Is K leaching an issue in AL soils?

Answer 57

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Question 58

Discuss environmental impacts of K.

Answer 58

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Question 59

Amount of K in plants, per dry matter basis?

Answer 59

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Question 60

In what kinds of plant processes is K involved?

Answer 60

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Question 61

How is K involved in the opening and closing of stomates?

Answer 61

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