Midterm 2 Flashcards
(107 cards)
1
Q
What are the conceptual divisions of soil OM?
A
Labile, Stabilized, and Recalcitrant pools of OM
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.
3
Q
How is biological fixation costly ?
A
- 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
4
Q
What are 5 types of plant available forms of N?
A
- Symbiotic biological fixation 2. Free-living biological fixation 3. Nox (lightening) 4. Fertilizers 5. Other (geological, pollution, wildfire
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.
6
Q
Name 2 inorganic reduced N foms
A
NH3 and NH4+
7
Q
Name 3 inorganic oxidized forms of N
A
Nox, N2O, NO3-
8
Q
What are 3 examples of organic N
A
urea, amino acids, proteins
9
Q
Where is most of the global N residing?
A
in the atmosphere - 78%
10
Q
Plants contain ____ % N by weight
A
1-6 %
11
Q
There is ____ N in the top 1-ft of cultivated soils
A
0.03 - 0.4%
12
Q
95% of N is in (inorganic/organic) form
A
organic, unavailable to plants
13
Q
True or False: NO2- is not important to plants
A
False but it is less common. Found in feed lots.
14
Q
Name the substrate and end product of nitrification
A
NH3 (substrate) –> NO3-
15
Q
What can be lost during both nitrification and denitrification?
A
N2O
16
Q
Why is more N2O lost from nitrifier denitrification (urea) than in (NH4)2SO4 soil?
A
the pH and NH4 concentration is greater
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
18
Q
Does Asymbiotic or Symbiotic fix more N ?
A
Symbiotic
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
20
Q
What two nutrients limit N fixation?
A
P and Mo as they can affect photosynthesis
21
Q
Name the substrate and end product of denitrification
A
NO3 (substrate)- —> N2
22
Q
True or False: NO and NO3- are toxic to microbes
A
True
23
Q
Plants absorb N as _____ & ____
A
NO3- and NH4+
24
Q
Do plants have a high tolerance for NH4+?
A
No - it can retard growth and restrict K+ uptake. Grasses have higher tolerance.
25
How does high NO3- uptake affect pH?
it will increase pH (more alkaline) which will increase cation absorption.
26
How does high NH4+ uptake affect pH?
it will decrease pH (more acidic) which will increase anion absorption. This can impact growth.
27
What are 3 functions of N in plants?
1. assimilated into amino acids/proteins 2. part of nucleic acid 3. part of chlorophyll
28
What is a symptom of excess N in plants?
delayed crop maturity, weak due to not enough C in cell wall
29
What are examples of organisms involved in biological N fixation?
Rhizobium, Actinomycetes, Blue-green Algae, Frankia
30
What 4 factors affect N2 fixation? Why?
soil pH (acidic soils), nutrient status, photosynthesis, and climate. All of these factors can inhibit rhizobial activity/growth
31
What are the two steps in N mineralization?
step 1 aminization and step 2 ammonification
32
What is synchrony in relation to N in soil and in plants?
N mineralization needs to correspond to crop N uptake. If synchrony is off, leaching can occur.
33
What is the fate of ammonium (NH4+)? 5 examples
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
34
What 6 factors affect nitrification?
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
35
Why does denitrification occur?
NO3 is toxic to microbes. Also, In anaerobic environments, microbes will obtain O2 from NO2- and NO3-.
36
What 8 factors affect denitrification?
1. decomposable OM 2. soil water content 3. aeration 4. soil pH 5. temperature 6. NO3- level 7. presence of plants 8. NO2- level
37
Where might NH4 get fixed in clays? What can bump it off ?
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
38
What is the most commonly used inorganic N source?
Anhydrous ammonia (NH3). Urea is the most common dry N as it behaves similar after hydrolization.
39
Is N mobile or immobile in plants?
mobile
40
Mobility of N in soil
NH4+ is immobile but NO3- is mobile
41
Deficiency symptoms of N in plants
chlorosis or necrosis in older leaves. Symptoms begin at the leaf tip and proceed along the midrib
42
What are the functions of P in plants?
P is a component of nucleic acids, ATP, NADP, and phospholipids. P is also a cofactor of some enzymes
43
What are deficiency symptoms of P in plants?
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
P forms absorbed by plants
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
How is P commonly lost in the soil?
erosion as P is concentrated near surface soil in the organic form
46
What pH is optimum for PO4 availability ?
pH 6.5
47
In pH <6.5 PO4 is not available because
PO4 is adsorbed to Fe-Al oxides and clays
48
In pH >6.5 PO4 is not available because
PO4 binds to Ca
49
Why will 1:1 clay impact P retention more than 2:1
Because of the broken edge effect
50
True or False: Monovalent cations adsorb more P than divalent cations on the CEC
False
51
How can you make P more available in the soil?
Flooding, base saturation, add fertilizer, add manure, add SOM
52
Mobility of P in plants vs. soil
P is mobile in plants but little/no mobility in soils
53
What is the most important P source (fertilizer)
Acid treatment P fertilizers that make rock phosphate more available. There are two types a. single superphosphate b. triple superphosphate
54
Forms of inorganic P in soil
Calcium phosphates, Iron & Aluminum phosphates, H2PO4-, HPO4^2-
55
What soils is Olsen-P test used for?
P test for alkaline and calcareous soils
56
What soils are Bray 1 or Mehlich 3 tests used for?
P test for acidic and neutral soils
57
Where does most of S come from?
volcanoes
58
What form(s) of S do plants uptake?
primarily SO4^2-. leaves can take up SO2
59
Plants contain __% S
0.1 - 0.5
60
In plants, S content increases in
[place these in order: Cruciferae, Gramineae, Leguminosae]
Gramineae
61
Where is 90% of S in plants found?
Amino acids
62
If a plant is experiencing S deficiency, what nutrient will they show an increase in?
non-protein N in the form of NH2 or NO3-
63
Give 3 examples of what S is important for in plants
1. protein structure 2. synthesis of coenzyme A 3. synthesis of chlorophyll
64
____ppm of SO4^2- is adequate for most plants
3-5 ppm
65
What are 6 forms (non specific) of S found in soil?
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
What depth is S found in soil?
Greater depth subsoils due to presence of Fe/Al oxides and clay
67
What are 5 sources of mineralizable S?
1. Humus 2. plant residues 3. microbial byproducts 4. mineralization closely related to C content 5. organic S in soils
68
Mineralization of S is (fast/slow).
slow, making it difficult to measure for prediction
69
What extractants would you use to pull S off sites?
Phosphate ions as they have a greater strength of adsorption
70
S is (mobile/immobile) in plants
mobile
71
2 symptoms of S deficiency
chlorosis in upper leaves and reduced plant growth
72
True or False: S is mobile in all soil tyles
False, immobile in very acidic soils
73
How to increase S in soil?
Add manure, ammonium sulfate, gypsum, magnesium sulfate, potassium sulfate
74
Form of Ca absorbed by plants and is it mobile?
Ca2+, immobile in the plant
75
True or False: Ca deficiencies are very common
False
76
Where would you expect to find Ca deficiencies?
highly leached and unlimed acidic soils
77
Ca in plants is ____%
0.2 - 1%
78
What 4 things is Ca important for the plant?
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
Ca in soil is ____ ppm
8 - 45 ppm
80
What type of soils have high Ca and why?
Arid soils due to low rainfall = less leaching (Calcite CaCO3)
81
The amount of Ca2+ available to plants depends on what 5 things?
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
Name 6 Ca fertilizer sources
1. single- and triple-superphosphate 2. CaEDTA 3. Phosphate rocks 4. Animal and municipal OM 5. Liming material 6. Egg shells
83
Ca is (immobile/mobile) in soils
immobile
84
What happens to Ca2+ in pH > 6.5?
precipitates as Ca-phosphate minerals
85
Plant symptoms of Ca2+ deficiency
stunted growth due to poor development of terminal buds and root tips. Necrosis of upper leaves
86
What form of Mg is absorbed by plants and is it mobile?
Mg2+, mobile
87
True or False: Plants take up less Mg compared to Ca and K
True
88
There is ____% of Mg in plants
0.1 - 0.4%
89
What 3 things is Mg important for the plant?
1. Chlorophyll 2. Protein formation 3. phosphate transfer in ATP reactions
90
What is grass tetany?
An Mg deficiency in cattle when they consume forages low in Mg.
91
What other cations may depress Mg in plant tissues?
NH4+ and K+
92
Mg in soil is ____ ppm
5 - 50
93
What can you apply to low-Mg acidic soils?
Dolomite
94
What are the most commonly used Mg dry fertilizers (common name)
epsom salts (magnesium sulfate)
95
Plant Mg deficiency symptoms
Interveinal chlorosis, necrosis, general withered appearance
96
Mg is (mobile/immobile) in soil
mobile
97
What happens to Mg in pH >7.2?
Mg availability decreases
98
What happens to Mg in very acidic soils?
low exchangeable Mg
99
True or false: addition of cations increases Mg uptake
False, reduces
100
What enzyme is responsible for N fixation?
Nitrogenase
101
Name: NH4
ammonium
102
Name: NH3
ammonia
103
Name: N2O
nitrous oxide
104
Name: N2
dinitrogen
105
Name: NO2-
nitrite
106
Name: NO3-
nitrate
107
Name: SO4^2-
sulfate
