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SSC 109 > Midterm 1 > Flashcards

Midterm 1 Flashcards

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
Q

What type of charge is on soil OM?

A

SOM is strongly pH dependent due to the O and OH groups

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26
Q

True or False: OM has a higher CEC than clay minerals

A

True

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27
Q

How many moles of Ca are needed to replace 2 moles of Al?

A

3 moles of Ca2+ are needed to replace 2 moles of Al3+.

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28
Q

True or False: Roots have CEC

A

True, mainly as carboxyl groups (-COOH)

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29
Q

What has more CEC: monocot or dicot

A

Dicot because surface area is lower so they need to make up for that

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30
Q

Define base saturation

A

the percent of the CEC occupied by Ca, Mg, K, and Na cations

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31
Q

How does base saturation affect soil pH?

A

When the soil surface takes up a base cation it needs to release an H+ which will lower pH

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32
Q

What are the acidic cations that occupy CEC

A

Al and H

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33
Q

What is Lyotrophic series and what impacts its strength?

A

Varying adsorption strengths of cations and anions that depend on valence and hydrated radius. Higher valence/hydrated radius = greater strength of adsorption

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34
Q

True or False: anions exhibit lyotrophic series

A

True. Certain anions are “sticker” than others. But this is more frequent with cations.

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35
Q

Which anion is the only one to have a hydrated radius?

A

Chloride [Cl-]

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36
Q

What is buffering capacity in soils?

A

The ability of the soil to re-supply an ion to the soil solution

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37
Q

What does buffering capacity affect?

A

nutrient availability and pH

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38
Q

What has a higher buffering capacity: clay or sandy soils

A

Clay soil has a higher buffering capacity and holds onto ions

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39
Q

True or False: if the product of the ions is > Ksp then the mineral will dissolve

A

False. If the product of the ions is < Ksp it will dissolve

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40
Q

Define mass flow

A

the transport of ions into the plant via the roots as it sucks up water

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41
Q

Define diffusion

A

the transport of ions into the plant through a concentration gradient (high to low)

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42
Q

Define interception

A

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.

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43
Q

What affects mass flow?

A

rate or volume of water consumption flow that can be decreased due to reduced transpiration

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44
Q

What affects diffusion?

A
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45
Q

What impacts the mobility of nutrients in soil?

A

quantity of nutrient in the soil and the quantity that is needed by the plants. Mobility will decrease as the nutrient deficiency increases

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46
Q

What nutrients have a high mobility in soil

A

Cl, Na, SO4, NO3

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47
Q

What nutrients have a medium mobility in soil

A

Ca, Mg, K, NH4

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48
Q

What nutrients have low mobility in soil

A

PO4, MoO4, Fe, Zn, Cu

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49
Q

Passive vs Active transport

A

In passive transport cells do not use energy

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50
Q

What are apoplastic pathways

A

Long distance nutrient transportation that is passively driven by diffusion, capillary action, and osmosis.

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51
Q

What issue can arise due to apoplastic pathways

A

nutrient imbalance

52
Q

What is beneficial about apoplastic pathway in nutrient uptake

A

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
Q

What is the symplastic pathway

A

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
Q

What is an “issue” with the symplastic pathway

A

Due to mass flow, plants are now able to select what nutrients come in

55
Q

What 3 affects does pH have on soil?

A
  1. Availability of plant nutrients 2. biological activity 3. solubility of soil minerals
56
Q

What is the optimum pH range for plant growth?

A

6.0 - 7.0

57
Q

What is the role of CO2 in soil pH?

A

CO2 is aq in soil solution and is a source of acidity before it dissolves into Bicarbonate and Hydrogen

58
Q

What are sources of CO2 in the soil?

A
  1. Microbial & root respiration
  2. Precipitation (acid rain)
59
Q

Name 6 broad sources of acidity in soils

A
  1. high precipitation that leads to leaching of base cations 2. soil OM mineralization (low effect) 3. Nutrient uptake and transformation
  2. leaching 5. clay minerals & oxides 6. soluble salts
60
Q

What is the role of Aluminum in soil acidity?

A

Dissociation of H+ from Al will cause acidity.

61
Q

True or False: Strong acids dissociate completely while weak acids dissociate weakly.

A

True

62
Q

Mycorrhizae help with the uptake of what?

A

nutrients (primarily P) and water

63
Q

During mass flow, nutrients first enter the root at _____ before they are ______.

A

1) Endodermis
2) Selected to move to vascular tissue/phloem

64
Q

Is Al3+ acidic when it is attached to soil?

A

No, it is only acidic once it is hydrolyzed in solution

65
Q

What is an acid forming fertilizer?

A

Ammonium [NH4+] because of the release of H+ during nitrification

66
Q

Common amendment for saline and sodic soils

A

Gypsum

67
Q

Amendment for severely sodic soils

A

Source of acid. Ex: Sulfuric Acid

68
Q

Most common form of N in soils

A

Nitrate [No3-]

69
Q

What are two sources of CO2 in soils?

A

Respiration via microbial community and precipitation (acid rain)

70
Q

What is an example of an acid dissociating an H+ in solution?

A

HCL –> Cl- + H+

71
Q

What is Kw?

A

the dissociation constant for water

72
Q

Define pH

A

-log [H+]

73
Q

Do weak acids dissociate completely? Give an example of a weak acid

A

No only strong acids do. Weak acids dissociate weakly. Example is acetic acid.

74
Q

Give 4 examples of nutrient uptake or transformation that lowers pH

A

Nitrification, Volatilization, NH4+ uptake, Sulfur mineralization

75
Q

Give 4 examples of nutrient uptake or transformation that increases pH

A

N mineralization, denitrification, urea hydrolysis, NO3- uptake

76
Q

What can be done to neutralize a soil that has acidity with Al3+?

A

Add carbonates (CaCO3) in solution to bind precipitate out Al(OH)3

77
Q

What has a higher buffering capacity: clay loam or sand?

A

clay loam has a higher buffering capacity. More limestone is required to raise surface pH.

78
Q

At low pH Phosphorous fixes to _____ and at high pH Phosphorous fixes to _____.

A

low = Fe and Al
high = Ca

79
Q

Why is Mg susceptible to leaching?

A

It can be displaced by Al or H on exchange sites.

80
Q

What pH range do microbes like?

A

neutral to alkaline. acidity affects microbial activity. (N)

81
Q

What is the liming reaction?

A

CaCO3 + 2H+ <–> Ca2+ + CO2 + H2O

82
Q

What happens to H+ in the liming reaction?

A

It is completely consumed by the reaction to raise the pH

83
Q

pH and base saturation have a _____ relationship

A

direct

84
Q

What is one of the more popular lime requirement tests and what does it measure?

A

SMP buffer pH test that measures the soil’s active and potential acidity

85
Q

What are the 6 types of liming materials?

A

CaCo3, CaO, Ca(OH)2, MgCO3, Marl, Slags

86
Q

Is Gypsum a good liming material?

A

No but it is good for saline or sodic soils

87
Q

What 2 important factors go into liming selection?

A
  1. Quality (composition) 2. Fineness
88
Q

The liming rate ____ with finer material

A

decreases

89
Q

Liming efficiency is lower with ____ material

A

coarser

90
Q

2 direct benefits of liming

A

decrease of Al+3, Mn2+ toxicity

91
Q

Give examples of indirect benefits of liming

A

Increase P availability through precipitation of Fe and Al, Micronutrient availability, Nitrification, N-fixation, decrease in fungal infections, microbial community activity, OM decomposition

92
Q

What is an acid forming fertilizer?

A

Ammonium

93
Q

Give examples of reactions that consume acidity

A

Aerobic respiration, denitrification, Mn reduction, Fe reduction, Sulfate reduction, CH4 production

94
Q

What are calcareous soils and where are they found?

A

soils that have native CaCO3, found in semi-arid regions. Low rainfall increases build up.

95
Q

Too much CaCO3 can cause ____ that can be corrected by ____

A

soil fertility issues, acidifying the soil

96
Q

Monovalent vs divalent sodium effect on soil structure

A

Monovalent Na+ causes repulsion/dispersion that breaks down the structure. Divalent Ca2+ causes attraction/floccultation.

97
Q

Salts originate from the _________ , ________, or from _______.

A

weathering of minerals, salt deposits left from ancient sea beds, human induced sources

98
Q

True or False: Saline soils are affected by any type of salt

A

True

99
Q

Saline soils have a pH of

A

<8.5

100
Q

Saline soils have an ESP of

A

<15%

101
Q

Saline soils have an ECse of

A

> 4mmho/cm

102
Q

True or False: Type of salt is not an issue with Sodic soils

A

False. High sodium (Na+) carbonates impact sodic

103
Q

Sodic soils have a ph of

A

> 8.5

104
Q

Sodic soils have an ESP of

A

> 15%

105
Q

Sodic soils have an ECse of

A

<4mmho/cm

106
Q

Saline-Sodic soils are impacted by

A

a high salt AND sodium content

107
Q

Saline-Sodic soils have a pH of

A

<8.5

108
Q

Saline-Sodic have an ESP of

A

> 15%

109
Q

Saline-Sodic have an ECse of

A

> 4mmho/cm

110
Q

Why do salts accumulate at soil surface

A

Evaporation

111
Q

Saline soils are referred to as ___

A

white alkali because of the dissolved salt on surface

112
Q

Sodic soils are referred to as _____

A

black alkali because of the dissolved OM on surface

113
Q

What does ECse stand for?

A

Electrical conductivity of saturated extract

114
Q

SAR is related to

A

the exchangeable Na+ ratio (ESR). ESR = base saturation analysis

115
Q

How to manage saline & saline-sodic soils?

A

Irrigation (not pure H2O), Gypsum

116
Q

How to manage sodic soils?

A

CaSO4/S, irrigation

117
Q

How to manage severely sodic soils?

A

Some type of acid - sulfuric acid

118
Q

How does salinity limit plant growth?

A

water imbalance in the plant which imbalances nutrient uptake and utilization of other cations, and can cause toxicity from Na+ and Cl-

119
Q

3 Symptoms of salt-affected plants

A

stunted growth, darker green leaf color, and leaf burn

120
Q

Crops are more sensitive to salt during ____ growth

A

early seedling

121
Q

Are crops in nutrient-poor soils more or less salt tolerant

A

More because they are taking up nutrients + salts

122
Q

Hot/dry conditions have a _____ salt tolerance because of _____

A

decreased, increased evapotranspiration

123
Q

How do you quantify salt tolerance?

A

calculating the relative yield loss

124
Q

Why would very clean water be unsuitable to leach a sodic affected soil?

A

There is nothing to exchange

125
Q

In a highly buffered you would use _____ limestone

A

coarse as it has a lower efficiency rate

SSC 109 (2 decks)

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