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SSC 109 > Midterm 1 > Flashcards

Midterm 1 Flashcards

(125 cards)

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1
Q

Factors leading to increased crop yields over the last century

A

Fertilizer N, Plant propagation, Herbicides, Row Spacing, Crop rotations, Planting date

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2
Q

What is the Law of the Minimum

A

Justus von Liebig used this term to describe how plant yield is directly related to the minimum or limiting nutrients. Plant yield is dependent on that specific limiting nutrient.

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3
Q

What are the 9 essential macronutrients (in order of highest concentration)

A

Oxygen, Carbon, Hydrogen, Nitrogen, Potassium, Phosphorous, Calcium, Magnesium, Sulfur

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4
Q

What are the 8 essential micronutrients (in order of highest concentration)

A

Chlorine, Iron, Boron, Manganese, Zinc, Copper, Molybdenum, Nickel

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5
Q

What are the 4 beneficial elements?

A

Sodium, Cobalt, Silicon, Selenium

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6
Q

True or False: Micronutrients are less important than macronutrients

A

False. They are just as important but are required in smaller amounts and may only be required by certain plants.

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7
Q

Symptoms of mobile v. non-mobile nutrients in plants

A

Mobile nutrients will show deficiency in old growth while non-mobile will only show in new plant growth.

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8
Q

What are the 6 mobile nutrients in plants

A

P, Mg, Cl, Mo, K, N

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9
Q

What are the 8 non-mobile nutrients in plants

A

Ni, Zn, B, Fe, Mn, Ca, S, Cu

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10
Q

What are the 3 criteria for nutrients to be “essential”?

A

Nutrients that are required for plant growth & reproduction, are specific & cannot be replaced, and that act directly

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11
Q

Plant nutrient composition (in %)

A

90% water, 10% solids (4% of which is mineral elements while the rest are CHO)

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12
Q

Essential v beneficial element for plants

A
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13
Q

True or False: It would be good to fertilize with selenium to increase crop yields

A

False. It is not useful for plants. Potential to accidentally do it by mineral blocks for livestock.

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14
Q

Define ion exchange

A

The exchange of cations on the negatively charged particle surface. The exchange is a reversible process via electrostatic forces (weaker) that controls plant available nutrients and retention in soil.

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15
Q

Define CEC as an equation

A

Cation exchange capacity that is described as 1 milliequivalents of charge (meq) per 100g soil.

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16
Q

1 meq/100 g soil is equal to

A

1 cmol/kg

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17
Q

What is important to know when calculating the CEC?

A

The atomic weight of elements (expressed as mole weight)

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18
Q

How does pH affect cation exchange?

A

At low pH there is a higher concentration of H+ and less cations binding. At high pH there is less H+ concentration and now cations will come in and bind at sites.

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19
Q

Describe 1:1 clay minerals

A

1:1 clay minerals are non-expansive, pH dependent, non-sticky, with low surface area and low cation exchange.

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20
Q

Describe 2:1 clay minerals

A

2:1 clay minerals are expansive & sticky, with a high surface area and high cation exchange. They have a constant/permanent charge if there is isomorphous substitution in one of the sheets.

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21
Q

Examples of 1:1 clay minerals

A

Kaolinite, Hallosyite

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22
Q

Examples of 2:1 clay minerals

A

Illite, Vermiculite, Chlorite, Smectite Montmorillonite

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23
Q

How could a 2:1 have a positive charge?

A

If Silica is substituted for Aluminum

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24
Q

What type of charge is on SOM and what is the source of it?

A

negative, hydroxides

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25
What type of charge is on soil OM?
SOM is strongly pH dependent due to the O and OH groups
26
True or False: OM has a higher CEC than clay minerals
True
27
How many moles of Ca are needed to replace 2 moles of Al?
3 moles of Ca2+ are needed to replace 2 moles of Al3+.
28
True or False: Roots have CEC
True, mainly as carboxyl groups (-COOH)
29
What has more CEC: monocot or dicot
Dicot because surface area is lower so they need to make up for that
30
Define base saturation
the percent of the CEC occupied by Ca, Mg, K, and Na cations
31
How does base saturation affect soil pH?
When the soil surface takes up a base cation it needs to release an H+ which will lower pH
32
What are the acidic cations that occupy CEC
Al and H
33
What is Lyotrophic series and what impacts its strength?
Varying adsorption strengths of cations and anions that depend on valence and hydrated radius. Higher valence/hydrated radius = greater strength of adsorption
34
True or False: anions exhibit lyotrophic series
True. Certain anions are "sticker" than others. But this is more frequent with cations.
35
Which anion is the only one to have a hydrated radius?
Chloride [Cl-]
36
What is buffering capacity in soils?
The ability of the soil to re-supply an ion to the soil solution
37
What does buffering capacity affect?
nutrient availability and pH
38
What has a higher buffering capacity: clay or sandy soils
Clay soil has a higher buffering capacity and holds onto ions
39
True or False: if the product of the ions is > Ksp then the mineral will dissolve
False. If the product of the ions is < Ksp it will dissolve
40
Define mass flow
the transport of ions into the plant via the roots as it sucks up water
41
Define diffusion
the transport of ions into the plant through a concentration gradient (high to low)
42
Define interception
the transport of ions into the plant as roots collide with nutrients as they move through the soil. Accounts for less than 1% of nutrient uptake by plants. Enhanced by mycorrhiza.
43
What affects mass flow?
rate or volume of water consumption flow that can be decreased due to reduced transpiration
44
What affects diffusion?
45
What impacts the mobility of nutrients in soil?
quantity of nutrient in the soil and the quantity that is needed by the plants. Mobility will decrease as the nutrient deficiency increases
46
What nutrients have a high mobility in soil
Cl, Na, SO4, NO3
47
What nutrients have a medium mobility in soil
Ca, Mg, K, NH4
48
What nutrients have low mobility in soil
PO4, MoO4, Fe, Zn, Cu
49
Passive vs Active transport
In passive transport cells do not use energy
50
What are apoplastic pathways
Long distance nutrient transportation that is passively driven by diffusion, capillary action, and osmosis.
51
What issue can arise due to apoplastic pathways
nutrient imbalance
52
What is beneficial about apoplastic pathway in nutrient uptake
Plant selects the amount/ratio of nutrients. Water/ions move until they reach the Casparian strip and are then selected for appropriate nutrient uptake
53
What is the symplastic pathway
Via mass flow, ions outside the endodermis must be actively transported into the endodermal cells. Once inside the endodermis, ions move via symplastic pathway. Ions move from cell to cell via plasmodesmata and are actively transported into the xylem.
54
What is an "issue" with the symplastic pathway
Due to mass flow, plants are now able to select what nutrients come in
55
What 3 affects does pH have on soil?
1. Availability of plant nutrients 2. biological activity 3. solubility of soil minerals
56
What is the optimum pH range for plant growth?
6.0 - 7.0
57
What is the role of CO2 in soil pH?
CO2 is aq in soil solution and is a source of acidity before it dissolves into Bicarbonate and Hydrogen
58
What are sources of CO2 in the soil?
1. Microbial & root respiration 2. Precipitation (acid rain)
59
Name 6 broad sources of acidity in soils
1. high precipitation that leads to leaching of base cations 2. soil OM mineralization (low effect) 3. Nutrient uptake and transformation 4. leaching 5. clay minerals & oxides 6. soluble salts
60
What is the role of Aluminum in soil acidity?
Dissociation of H+ from Al will cause acidity.
61
True or False: Strong acids dissociate completely while weak acids dissociate weakly.
True
62
Mycorrhizae help with the uptake of what?
nutrients (primarily P) and water
63
During mass flow, nutrients first enter the root at _____ before they are ______.
1) Endodermis 2) Selected to move to vascular tissue/phloem
64
Is Al3+ acidic when it is attached to soil?
No, it is only acidic once it is hydrolyzed in solution
65
What is an acid forming fertilizer?
Ammonium [NH4+] because of the release of H+ during nitrification
66
Common amendment for saline and sodic soils
Gypsum
67
Amendment for severely sodic soils
Source of acid. Ex: Sulfuric Acid
68
Most common form of N in soils
Nitrate [No3-]
69
What are two sources of CO2 in soils?
Respiration via microbial community and precipitation (acid rain)
70
What is an example of an acid dissociating an H+ in solution?
HCL --> Cl- + H+
71
What is Kw?
the dissociation constant for water
72
Define pH
-log [H+]
73
Do weak acids dissociate completely? Give an example of a weak acid
No only strong acids do. Weak acids dissociate weakly. Example is acetic acid.
74
Give 4 examples of nutrient uptake or transformation that lowers pH
Nitrification, Volatilization, NH4+ uptake, Sulfur mineralization
75
Give 4 examples of nutrient uptake or transformation that increases pH
N mineralization, denitrification, urea hydrolysis, NO3- uptake
76
What can be done to neutralize a soil that has acidity with Al3+?
Add carbonates (CaCO3) in solution to bind precipitate out Al(OH)3
77
What has a higher buffering capacity: clay loam or sand?
clay loam has a higher buffering capacity. More limestone is required to raise surface pH.
78
At low pH Phosphorous fixes to _____ and at high pH Phosphorous fixes to _____.
low = Fe and Al high = Ca
79
Why is Mg susceptible to leaching?
It can be displaced by Al or H on exchange sites.
80
What pH range do microbes like?
neutral to alkaline. acidity affects microbial activity. (N)
81
What is the liming reaction?
CaCO3 + 2H+ <--> Ca2+ + CO2 + H2O
82
What happens to H+ in the liming reaction?
It is completely consumed by the reaction to raise the pH
83
pH and base saturation have a _____ relationship
direct
84
What is one of the more popular lime requirement tests and what does it measure?
SMP buffer pH test that measures the soil's active and potential acidity
85
What are the 6 types of liming materials?
CaCo3, CaO, Ca(OH)2, MgCO3, Marl, Slags
86
Is Gypsum a good liming material?
No but it is good for saline or sodic soils
87
What 2 important factors go into liming selection?
1. Quality (composition) 2. Fineness
88
The liming rate ____ with finer material
decreases
89
Liming efficiency is lower with ____ material
coarser
90
2 direct benefits of liming
decrease of Al+3, Mn2+ toxicity
91
Give examples of indirect benefits of liming
Increase P availability through precipitation of Fe and Al, Micronutrient availability, Nitrification, N-fixation, decrease in fungal infections, microbial community activity, OM decomposition
92
What is an acid forming fertilizer?
Ammonium
93
Give examples of reactions that consume acidity
Aerobic respiration, denitrification, Mn reduction, Fe reduction, Sulfate reduction, CH4 production
94
What are calcareous soils and where are they found?
soils that have native CaCO3, found in semi-arid regions. Low rainfall increases build up.
95
Too much CaCO3 can cause ____ that can be corrected by ____
soil fertility issues, acidifying the soil
96
Monovalent vs divalent sodium effect on soil structure
Monovalent Na+ causes repulsion/dispersion that breaks down the structure. Divalent Ca2+ causes attraction/floccultation.
97
Salts originate from the _________ , ________, or from _______.
weathering of minerals, salt deposits left from ancient sea beds, human induced sources
98
True or False: Saline soils are affected by any type of salt
True
99
Saline soils have a pH of
<8.5
100
Saline soils have an ESP of
<15%
101
Saline soils have an ECse of
>4mmho/cm
102
True or False: Type of salt is not an issue with Sodic soils
False. High sodium (Na+) carbonates impact sodic
103
Sodic soils have a ph of
>8.5
104
Sodic soils have an ESP of
>15%
105
Sodic soils have an ECse of
<4mmho/cm
106
Saline-Sodic soils are impacted by
a high salt AND sodium content
107
Saline-Sodic soils have a pH of
<8.5
108
Saline-Sodic have an ESP of
>15%
109
Saline-Sodic have an ECse of
>4mmho/cm
110
Why do salts accumulate at soil surface
Evaporation
111
Saline soils are referred to as ___
white alkali because of the dissolved salt on surface
112
Sodic soils are referred to as _____
black alkali because of the dissolved OM on surface
113
What does ECse stand for?
Electrical conductivity of saturated extract
114
SAR is related to
the exchangeable Na+ ratio (ESR). ESR = base saturation analysis
115
How to manage saline & saline-sodic soils?
Irrigation (not pure H2O), Gypsum
116
How to manage sodic soils?
CaSO4/S, irrigation
117
How to manage severely sodic soils?
Some type of acid - sulfuric acid
118
How does salinity limit plant growth?
water imbalance in the plant which imbalances nutrient uptake and utilization of other cations, and can cause toxicity from Na+ and Cl-
119
3 Symptoms of salt-affected plants
stunted growth, darker green leaf color, and leaf burn
120
Crops are more sensitive to salt during ____ growth
early seedling
121
Are crops in nutrient-poor soils more or less salt tolerant
More because they are taking up nutrients + salts
122
Hot/dry conditions have a _____ salt tolerance because of _____
decreased, increased evapotranspiration
123
How do you quantify salt tolerance?
calculating the relative yield loss
124
Why would very clean water be unsuitable to leach a sodic affected soil?
There is nothing to exchange
125
In a highly buffered you would use _____ limestone
coarse as it has a lower efficiency rate

SSC 109 (2 decks)

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