Need in one hour. I posted the lectures reading.  It has 11 questions

Quick Questions

Question 61

 

(5 points)

 

What is cation exchange capacity and why is it such an important soil component?

Question 62 (5 points)

 

Discuss the ecological effects of poor aeration and waterlogged soil conditions; include details on how the microbial community is changed, the plant, animal and microbial availability of soil nutrients, how soil color changes, changes in soil off-gasses, and potential plant root/shoot problems.

Question 63 (5 points)

 

Define isomorphic substitution: Include a definition, where it occurs, discuss what ions might be included in isomorphic substitution, and name three clays in which their charge is dependent on isomorphic substitution.

Question 64 (4 points)

 

List and discuss the four main principles that govern cation exchange.

Question 65 (3 points)

 

Explain the role texture plays in the speed, sorption, and movement of water in soils.

Question 66 (3 points)

 

Discuss at least three environmental benefits of wetlands.

Question 67 (3 points)

 

Why do no-till farmers sometimes have to wait a few more days to get in the field in the spring than farmers who use traditional till?

Question 68 (3 points)

 
Explain the role texture plays in the speed, sorption, and movement of water in soils.

Question 69 (3 points)

 

Describe soil water potential (including approximate quantities) as it moves from soil, up thru a plant, into the atmosphere, and back to the soil in the form of precipitatio

Question 70 (3 points)

 

Why would farmers in arid regions utilize the practice of leaving a particular field fallow for part of a potential growing season? What ramifications both positive and negative might this have on soil moisture and conservation?

Question 71 (3 points)

 

Explain the pros and cons of artificial drainage. How might it be positive from an agronomic perspective, but negative from an environmental one?

2/21/2020 Soil Water (Chapter 5) Notes – AGRI1050R50: Introduction to Soil Science (2020S)

https://gotoclass.tnecampus.org/d2l/le/content/8094442/viewContent/60403374/View 1/6

Soil Water (Chapter 5) Notes

Soil Water (Chapter 5) Notes

Did you know ….
Did you know that only 3% of the water on earth is fresh water? And that soils play a very important part in the
movement and filtering of water before we find it in our taps. Chapter 5 will start our discussion on water and
soils and includes discussion of water’s properties that make it so unique, energ of water movement in in soils,
measuring water content in soils, and how water becomes plant available.

Lecture content notes are accompanied by videos listed below the notes in each submodule (e.g. Soil Water
(Chapter 5) Videos A though C). Print or download lecture notes then view videos in succession alongside
lecture content and add additional notes from each video. The start of each video is noted in parenthesis (e.g.
Content for Video A) within each lecture note set and contains lecture content through the note for the next
video (e.g. Content for Video B).

Figures and tables unless specifically referrenced are from the course text, Nature and Property of Soils, 14th
Edition, Brady and Weil.

Content Video A

Soil Water

“When the well is dry, we will know the importance of water.” Benjamin Franklin

Water Trivia
Only 3% of Earth’s water is fresh water. 97% of the water on Earth is salt water.

Water covers 70.9% of the Earth’s surface.

There is more fresh water in the atmosphere than in all of the rivers on the planet combined.

American residents use about 100 gallons of water per day

AGRI1050R50: Introduction to Soil Science (2020S) LH

https://gotoclass.tnecampus.org/d2l/le/content/8094442/navigateContent/140/Previous?pId=60403301

https://gotoclass.tnecampus.org/d2l/le/content/8094442/navigateContent/140/Next?pId=60403301

https://gotoclass.tnecampus.org/d2l/common/dialogs/quickLink/quickLink.d2l?ou=8094442&type=content&rcode=TBR-23955744

https://gotoclass.tnecampus.org/d2l/home/8094442

2/21/2020 Soil Water (Chapter 5) Notes – AGRI1050R50: Introduction to Soil Science (2020S)

https://gotoclass.tnecampus.org/d2l/le/content/8094442/viewContent/60403374/View 2/6

American residents use about 100 gallons of water per day.

The first water pipes were made from wood.

More than 25% of bottled water comes from a municipal water supply, the same place that tap water
comes from.

An inch of water covering one acre (27,154 gallons) weighs 113 tons.

Water makes up between 55-78% of a human’s body weight.

Data courtesy of USEPA

Structure and Properties
Polarity

Hydrogen Bonding

Cohesion – Stick together

Adhesion – Stick to other materials

Hydration

Surface Tension

Capillary Action

2/21/2020 Soil Water (Chapter 5) Notes – AGRI1050R50: Introduction to Soil Science (2020S)

https://gotoclass.tnecampus.org/d2l/le/content/8094442/viewContent/60403374/View 3/6

Content Video B

It’s all about the …… Energy
HI to LOW

Relative not absolute values – Difference determines direction of movement

Potential – standard atmospheric pressure (bar) or Pascal

Gravitational

Osmotic

Matrix

Freedom of movement –Wet vs Dry Soils

Water Content and Potential

Measuring Soil Water

https://gotoclass.tnecampus.org/d2l/common/dialogs/quickLink/quickLink.d2l?ou=8094442&type=content&rcode=TBR-23955926

2/21/2020 Soil Water (Chapter 5) Notes – AGRI1050R50: Introduction to Soil Science (2020S)

https://gotoclass.tnecampus.org/d2l/le/content/8094442/viewContent/60403374/View 4/6

Movement of Water in Soils
Saturated Flow

Heavy Rain – Fast

Hydraulic Gradient (Table 5.3)

Contamination and Loss – pesticides, nutrients , pathogens

Unsaturated Flow

Dominant movement of water

Texture

Driven by matric potential

Slow

Stratified Layer

Major textural change – Fragipan

Changes flow routes

Positive or Negative – Box 5.3

Vapor Flow

Wetting Front

2/21/2020 Soil Water (Chapter 5) Notes – AGRI1050R50: Introduction to Soil Science (2020S)

https://gotoclass.tnecampus.org/d2l/le/content/8094442/viewContent/60403374/View 5/6

Reflect in ePortfolio Download Print

Content Video C

Qualitative Descriptions
Maximum Retentive Capacity – water saturated

Field Capacity

Plants with adequate water

Moisture is adequate but not too high for activities

Proper aeration for microbial community

Permanent Wilting Coefficient – Wilting Point

Hydroscopic Coefficient

Plant-Available Soil Water
Texture

Organic Matter

Compaction

Roots

Capillary Action

Root Extension

Task: View this topic

Activity Details

https://gotoclass.tnecampus.org/d2l/le/content/8094442/navigateContent/140/Previous?pId=60403301

https://gotoclass.tnecampus.org/d2l/le/content/8094442/navigateContent/140/Next?pId=60403301

https://gotoclass.tnecampus.org/d2l/common/dialogs/quickLink/quickLink.d2l?ou=8094442&type=content&rcode=TBR-23955974

javascript:void(0);

2/21/2020 Soil Water (Chapter 5) Notes – AGRI1050R50: Introduction to Soil Science (2020S)

https://gotoclass.tnecampus.org/d2l/le/content/8094442/viewContent/60403374/View 6/6

2/21/2020 Soil Aeration and Temperature (Chapter 7) Notes – AGRI1050R50: Introduction to Soil Science (2020S)

https://gotoclass.tnecampus.org/d2l/le/content/8094442/viewContent/60403383/View 1/8

Soil Aeration and Temperature (Chapter 7) Notes

Soil Aeration and Temperature (Chapter 7) Notes

Did you know ….
Did you know wetlands play a critical role in soil and water interactions and have many ecological positives?
Chapter 7 will cover soil aeration and temperature including how water and temperature effect soil properties
and functions as well as wetlands.

Lecture content notes are accompanied by videos listed below the notes in each submodule (e.g. Soil Aeration
and Temperature (Chapter 7) Videos A though D). Print or download lecture notes then view videos in
succession alongside lecture content and add additional notes from each video. The start of each video is
noted in parenthesis (e.g. Content for Video A) within each lecture note set and contains lecture content
through the note for the next video (e.g. Content for Video B).

Figures and tables unless specifically referrenced are from the course text, Nature and Property of Soils, 14th
Edition, Brady and Weil. .

Content Video A

Soil Aeration and Temperature
‘Land, then is not merely soil; it is the fountain of energy flowing through a circuit of soils, plants, and
anumals.’
Aldo Leopod, A Sand County Almanac, 1949

Soil Air Composition and Exchange

AGRI1050R50: Introduction to Soil Science (2020S) LH

https://gotoclass.tnecampus.org/d2l/le/content/8094442/navigateContent/162/Previous?pId=60403303

https://gotoclass.tnecampus.org/d2l/le/content/8094442/navigateContent/162/Next?pId=60403303

https://gotoclass.tnecampus.org/d2l/common/dialogs/quickLink/quickLink.d2l?ou=8094442&type=content&rcode=TBR-23958528

https://gotoclass.tnecampus.org/d2l/home/8094442

2/21/2020 Soil Aeration and Temperature (Chapter 7) Notes – AGRI1050R50: Introduction to Soil Science (2020S)

https://gotoclass.tnecampus.org/d2l/le/content/8094442/viewContent/60403383/View 2/8

Soil Gases and Aeration
Respiration – Ventilation

Oxygen Availability

Macroporosity

Water content

Oxygen consumption

Oxygen limited: 0.1 L/L

80-90% Pore Space Water – 10-20% Air

Microbial Activity / Root Respiration limited

Water Saturation – Water Logged

http://www.tn.gov/tsla/exhibits/disasters/newmadrid.htm

Redox
Redox Potential – Eh – potential to transfer electrons

Ionic Species – Valence State – Availability

Oxygen – Oxidizing Agent – TEA

Important Notes:
Iron Looses Electron – 2+ to 3+ – Electrons are negatively charged, so it increases valence state.

Lower the pH – Produced an H+

BALANCE – Oxidation – Reduction

http://www.tn.gov/tsla/exhibits/disasters/newmadrid.htm

2/21/2020 Soil Aeration and Temperature (Chapter 7) Notes – AGRI1050R50: Introduction to Soil Science (2020S)

https://gotoclass.tnecampus.org/d2l/le/content/8094442/viewContent/60403383/View 3/8

Table 7.1 Common Soil Inorganics Reduced/Oxidized Forms

Aerated/Oxidizing Conditions: Eh 0.4 to 0.7 Volts

Anaerobic/Reducing Conditions: Eh 0.32 to 0.38 Volts

Content Video B

Ecological Effects Soil Aeration
Microbial Community – Residue Breakdown

Inorganic Elements – Redox

Heavy Metals – Toxic

Soil Colors – Redox Status – Iron and Manganese

Greenhouse Gas Emission

Plant Roots – Oxygen needed

Content Video C

Wetlands
Wet/Saturated/Anaerobic Conditions

Hydric Soils

Periods of saturation – Diffusion of Oxygen into soil limited

Reducing conditions

Redoxomorphic features

Hydrophytic plants

Wetland Value
Species Habitat

Water Filtration

Flooding Reduction

Shoreline Protection

Recreation

https://gotoclass.tnecampus.org/d2l/common/dialogs/quickLink/quickLink.d2l?ou=8094442&type=content&rcode=TBR-23956139

https://gotoclass.tnecampus.org/d2l/common/dialogs/quickLink/quickLink.d2l?ou=8094442&type=content&rcode=TBR-23958580

2/21/2020 Soil Aeration and Temperature (Chapter 7) Notes – AGRI1050R50: Introduction to Soil Science (2020S)

https://gotoclass.tnecampus.org/d2l/le/content/8094442/viewContent/60403383/View 4/8

Recreation

http://photogallery.nrcs.usda.gov/res/sites/photogallery/

Content Video D

Soil Temperature

http://photogallery.nrcs.usda.gov/res/sites/photogallery/

https://gotoclass.tnecampus.org/d2l/common/dialogs/quickLink/quickLink.d2l?ou=8094442&type=content&rcode=TBR-23958581

2/21/2020 Soil Aeration and Temperature (Chapter 7) Notes – AGRI1050R50: Introduction to Soil Science (2020S)

https://gotoclass.tnecampus.org/d2l/le/content/8094442/viewContent/60403383/View 5/8

More Processes Affected by Temperature
Freeze/Thaw (f) – Frost Heaving (g)

Forrest Fire – Surface temperature increase, movement VOC downward, decreased infiltration rates

2/21/2020 Soil Aeration and Temperature (Chapter 7) Notes – AGRI1050R50: Introduction to Soil Science (2020S)

https://gotoclass.tnecampus.org/d2l/le/content/8094442/viewContent/60403383/View 6/8

Content Video E

Soil Temperature
Temperature

Solar Radiation:

Small percentage used to heat soil

Lots of interception

Specific Heat

Energy for evaporation

Albedo – Reflection back off the surface

Aspect – Angle of the sun

Thermal Properties
Specific Heat amount of energy required to increase the temperature of water by 1°C

https://gotoclass.tnecampus.org/d2l/common/dialogs/quickLink/quickLink.d2l?ou=8094442&type=content&rcode=TBR-23958584

2/21/2020 Soil Aeration and Temperature (Chapter 7) Notes – AGRI1050R50: Introduction to Soil Science (2020S)

https://gotoclass.tnecampus.org/d2l/le/content/8094442/viewContent/60403383/View 7/8

Specific Heat – amount of energy required to increase the temperature of water by 1 C

Heat of Vaporization – energy for evaporation HI

Thermal Conductivity

Managing Soil Temperature

2/21/2020 Soil Aeration and Temperature (Chapter 7) Notes – AGRI1050R50: Introduction to Soil Science (2020S)

https://gotoclass.tnecampus.org/d2l/le/content/8094442/viewContent/60403383/View 8/8

Reflect in ePortfolio Download Print

Task: View this topic

Activity Details

https://gotoclass.tnecampus.org/d2l/le/content/8094442/navigateContent/162/Previous?pId=60403303

https://gotoclass.tnecampus.org/d2l/le/content/8094442/navigateContent/162/Next?pId=60403303

javascript:void(0);

2/21/2020 Soil and Hydrologic Cycle (Chapter 6) Notes – AGRI1050R50: Introduction to Soil Science (2020S)

https://gotoclass.tnecampus.org/d2l/le/content/8094442/viewContent/60403378/View 1/8

Soil and Hydrologic Cycle (Chapter 6) Notes

Soil and Hydrologic Cycle (Chapter 6) Notes

Did you know ….
Did you know that the majority of the water you drink comes from underground aquifers? And that soils play a
very important part keeping that water clean for consumption. Chapter 6 continue our discussion on water and
soils and includes discussion of the global hydrologic cycle and soils role in it, what happens to water when it
comes in contact with the soil surface, how water moves from the soil up through the plants and out throgh the
leaves, controlling water loss, and managment of soil water.

Lecture content notes are accompanied by videos listed below the notes in each submodule (e.g. Soil and
Hydrologic Cycle (Chapter 6) Videos A though D). Print or download lecture notes then view videos in
succession alongside lecture content and add additional notes from each video. The start of each video is
noted in parenthesis (e.g. Content for Video A) within each lecture note set and contains lecture content
through the note for the next video (e.g. Content for Video B).

Figures and tables unless specifically referrenced are from the course text, Nature and Property of Soils, 14th
Edition, Brady and Weil.

Content Video A

Hydrologic Cycle

AGRI1050R50: Introduction to Soil Science (2020S) LH

https://gotoclass.tnecampus.org/d2l/le/content/8094442/navigateContent/150/Previous?pId=60403302

https://gotoclass.tnecampus.org/d2l/le/content/8094442/navigateContent/150/Next?pId=60403302

https://gotoclass.tnecampus.org/d2l/common/dialogs/quickLink/quickLink.d2l?ou=8094442&type=content&rcode=TBR-23956135

https://gotoclass.tnecampus.org/d2l/home/8094442

2/21/2020 Soil and Hydrologic Cycle (Chapter 6) Notes – AGRI1050R50: Introduction to Soil Science (2020S)

https://gotoclass.tnecampus.org/d2l/le/content/8094442/viewContent/60403378/View 2/8

Fate and Transport
P = ET + SS + D

Interception

Infiltration

Runoff

Soil Storage Water

Vegetation

Cover

Stem Flow

Soil Texture

Soil Management

Maintain cover

Increase structure

Decrease compaction

Soils and Urban Development

Content Video B

https://gotoclass.tnecampus.org/d2l/common/dialogs/quickLink/quickLink.d2l?ou=8094442&type=content&rcode=TBR-23956139

2/21/2020 Soil and Hydrologic Cycle (Chapter 6) Notes – AGRI1050R50: Introduction to Soil Science (2020S)

https://gotoclass.tnecampus.org/d2l/le/content/8094442/viewContent/60403378/View 3/8

Soil-Plant-Atmosphere Continuum

Vapor Loss
Evapotranspiration – Evaporation + Transpiration

PET – Potential ET

Factors Effecting ET:

Soil Moisture

Plant Stress

Solar Radiation – LAI

2/21/2020 Soil and Hydrologic Cycle (Chapter 6) Notes – AGRI1050R50: Introduction to Soil Science (2020S)

https://gotoclass.tnecampus.org/d2l/le/content/8094442/viewContent/60403378/View 4/8

Water Efficiency
Tremendous amount of water to produce our food and fiber.

Efficiency peaks at ~1kg dry matter/1000 kg or m3 of water

Content Video C

Control ET Loss
Transpiration – Plant loss

Evaporation – Soil Surface Loss

Vegetative Cover

Crop Residue

Mulch

https://gotoclass.tnecampus.org/d2l/common/dialogs/quickLink/quickLink.d2l?ou=8094442&type=content&rcode=TBR-23956156

2/21/2020 Soil and Hydrologic Cycle (Chapter 6) Notes – AGRI1050R50: Introduction to Soil Science (2020S)

https://gotoclass.tnecampus.org/d2l/le/content/8094442/viewContent/60403378/View 5/8

Vegetables – Plastic

Irrigation

– drip

http://photogallery.nrcs.usda.gov/res/sites/photogallery/

Liquid Losses

Memphis Sand Aquifer

http://photogallery.nrcs.usda.gov/res/sites/photogallery/

2/21/2020 Soil and Hydrologic Cycle (Chapter 6) Notes – AGRI1050R50: Introduction to Soil Science (2020S)

https://gotoclass.tnecampus.org/d2l/le/content/8094442/viewContent/60403378/View 6/8

p q

http://pubs.usgs.gov/wri/wrir88-4182/pdf/wrir_88-4182_a

Content for Video D

Artificial Drains

http://pubs.usgs.gov/wri/wrir88-4182/pdf/wrir_88-4182_a

https://gotoclass.tnecampus.org/d2l/common/dialogs/quickLink/quickLink.d2l?ou=8094442&type=content&rcode=TBR-23956159

2/21/2020 Soil and Hydrologic Cycle (Chapter 6) Notes – AGRI1050R50: Introduction to Soil Science (2020S)

https://gotoclass.tnecampus.org/d2l/le/content/8094442/viewContent/60403378/View 7/8

Septic Tanks

Irrigation

2/21/2020 Soil and Hydrologic Cycle (Chapter 6) Notes – AGRI1050R50: Introduction to Soil Science (2020S)

https://gotoclass.tnecampus.org/d2l/le/content/8094442/viewContent/60403378/View 8/8

Reflect in ePortfolio Download Print

Task: View this topic

Activity Details

https://gotoclass.tnecampus.org/d2l/le/content/8094442/navigateContent/150/Previous?pId=60403302

https://gotoclass.tnecampus.org/d2l/le/content/8094442/navigateContent/150/Next?pId=60403302

javascript:void(0);

2/21/2020Soil Colloids (Chapter 8) Notes – AGRI1050R50: Introduction to Soil Science (2020S)

https://gotoclass.tnecampus.org/d2l/le/content/8094442/viewContent/60403389/View 1/12

Soil Colloids (Chapter 8) Notes

Soil Colloids (Chapter 8) Notes

Did you know ….
Did you know soil fertility or the ability for a soil to provide nutrients is seated in the type of minerals it
contains? Chapter 8 will cover the various types of soil colloids including all the layer and non-layer
silicates, cation exchange, anion exchange, and sorption.

Lecture content notes are accompanied by videos listed below the notes in each submodule (e.g. Soil
Colloids (Chapter 8) Videos A though H). Print or download lecture notes then view videos in
succession alongside lecture content and add additional notes from each video. The start of each
video is noted in parenthesis (e.g. Content for Video A) within each lecture note set and contains
lecture content through the note for the next video (e.g. Content for Video B).

Figures and tables unless specifically referrenced are from the course text, Nature and Property of
Soils, 14th Edition, Brady and Weil.

Content Video A

Soil Colloids

Smallest soil particles < 1 µm Surface area - LARGE Surface charge - CEC Adsorb water

AGRI1050R50: Introduction to Soil Science (2020S) LH

https://gotoclass.tnecampus.org/d2l/le/content/8094442/navigateContent/176/Previous?pId=60403304

https://gotoclass.tnecampus.org/d2l/le/content/8094442/navigateContent/176/Next?pId=60403304

https://gotoclass.tnecampus.org/d2l/common/dialogs/quickLink/quickLink.d2l?ou=8094442&type=content&rcode=TBR-23958617

https://gotoclass.tnecampus.org/d2l/home/8094442

2/21/2020 Soil Colloids (Chapter 8) Notes – AGRI1050R50: Introduction to Soil Science (2020S)

https://gotoclass.tnecampus.org/d2l/le/content/8094442/viewContent/60403389/View 2/12

Types of Colloids
Crystalline Silicate clays: ordered, crystalline, layers
Non-crystalline silicate clays: non-ordered, layers, volcanic
Iron/Aluminum Oxides – weathered soils, less CEC
Humus – OM, not mineral or crystalline, high CEC

Soil Colloids

Content Video B

Layer Silicates – Construction
Phyllosillicates
Tetrahedral Sheets

1 Si with 4 Oxygen
Share basal oxygen
Form sheets

Octahedral Sheets
6 Oxygen with Al3+ or Mg 2+
Di T i O t h d l b d # f di ti i

https://gotoclass.tnecampus.org/d2l/common/dialogs/quickLink/quickLink.d2l?ou=8094442&type=content&rcode=TBR-23958618

2/21/2020 Soil Colloids (Chapter 8) Notes – AGRI1050R50: Introduction to Soil Science (2020S)

https://gotoclass.tnecampus.org/d2l/le/content/8094442/viewContent/60403389/View 3/12

Di or Tri Octahedral based on # of coordinating ions

http://web.utk.edu/~drtd0c/Soil%20Colloids

http://web.utk.edu/~drtd0c/Soil%20Colloids

2/21/2020 Soil Colloids (Chapter 8) Notes – AGRI1050R50: Introduction to Soil Science (2020S)

https://gotoclass.tnecampus.org/d2l/le/content/8094442/viewContent/60403389/View 4/12

Size and Charge
Isomorphic substitution and surface charge

Content Video C

1:1 Silicate Clays
Kaolinite
Hydrogen bonding – Fixed Structure
Low Isomorphic Substitution
Relatively low CEC
Water Holding capacity lower most clays
Inert clay – lots of uses

2:1 Silicate Clays
Expanding Type Minerals

Smectites
Isomorphic substitution high – CEC
Oxygen bonding – weak
Shrink-swell clays
Montmorillonite

Vermiculites
Isomorphic substitution high again – Highest CEC of 2:1
Interlayer space smaller, ions/water held tighter
Less shrink/swell than smectites

Non-Expanding Type Minerals
Fine-grained Micas

Illites and Glauconites
Al 3+ for Si4+ – Strong Negative – K+ fits/satisfies charge
Non-Expansive

Chlorites

https://gotoclass.tnecampus.org/d2l/common/dialogs/quickLink/quickLink.d2l?ou=8094442&type=content&rcode=TBR-23958694

2/21/2020 Soil Colloids (Chapter 8) Notes – AGRI1050R50: Introduction to Soil Science (2020S)

https://gotoclass.tnecampus.org/d2l/le/content/8094442/viewContent/60403389/View 5/12

2:1:1 with Mg2+ in the octahedral sheets
Hydrogen bonding – strong
CEC and physical properties similar to fine-grained micas

Review Silicate Layer Clays

Content Video D

Non-Silicate Clays
Iron/Aluminum Oxides

No silica
No tetrahedral sheets
Al3+ and Fe3+ main cations
Low Isomorphic Substitution, Low CEC, Sorb P
Non-Expansive – Low surface area
Gibbsite – Aluminum Hydroxide
Goethite – Iron Hydroxide

Humus – OM
Non-Crystalline
Carbon based
Difficult to characterize
HI CEC
Vital to soil fertility

https://gotoclass.tnecampus.org/d2l/common/dialogs/quickLink/quickLink.d2l?ou=8094442&type=content&rcode=TBR-23958695

2/21/2020 Soil Colloids (Chapter 8) Notes – AGRI1050R50: Introduction to Soil Science (2020S)

https://gotoclass.tnecampus.org/d2l/le/content/8094442/viewContent/60403389/View 6/12

Soil Colloids

Where did you come from, where did you go?

Soil Orders – Major Colloids

2/21/2020 Soil Colloids (Chapter 8) Notes – AGRI1050R50: Introduction to Soil Science (2020S)

https://gotoclass.tnecampus.org/d2l/le/content/8094442/viewContent/60403389/View 7/12

Content Video E

Sources of Charge
Isomorphic Substitution – Constant Charge

Net Negative Charge
2:1 layer clays
Mg2+ for Al 3+ – octahedral sheets
Al 3+ for Si4+ – tetrahedral sheets

Net Positive Charge
Less common
Al 3+ for Mg2+

pH dependent – Variable Charge
Mostly negative charges
Basic pH
OH groups
Broken Edges
Important in 1:1 (Kaolinite) and Iron/Aluminum Hydroxide
Some positive charge
Moderate/Extreme Acidity
Humus – Wide Range +/- sites

https://gotoclass.tnecampus.org/d2l/common/dialogs/quickLink/quickLink.d2l?ou=8094442&type=content&rcode=TBR-23958834

2/21/2020 Soil Colloids (Chapter 8) Notes – AGRI1050R50: Introduction to Soil Science (2020S)

https://gotoclass.tnecampus.org/d2l/le/content/8094442/viewContent/60403389/View 8/12

Sources of Charge Review

d

Content Video F

Sources of Charge
Outer–sphere complex:

Waters bridges
Weak attraction

Inner-sphere complex
Direct bonding to colloid

CATION EXCHANGE

https://gotoclass.tnecampus.org/d2l/common/dialogs/quickLink/quickLink.d2l?ou=8094442&type=content&rcode=TBR-23958908

2/21/2020 Soil Colloids (Chapter 8) Notes – AGRI1050R50: Introduction to Soil Science (2020S)

https://gotoclass.tnecampus.org/d2l/le/content/8094442/viewContent/60403389/View 9/12

Cation Exchange
Reversible
Stoichiometric Balance – cmolc “neutralized”
Mass Balance – Le Chatelier’s Principle

Flood the system, cation will replace on the exchange
Loss/precipitation of product will pull reaction in one direction, loss of reversibility

Selectivity – Size and Charge
Higher Charge, Smaller Radii > Stronger adsorption
Lyotrophic Series
Al3+ > Sr2+ > Ca2+ > Mg2+ > Cs+ > K+ = NH4+ > Na+ > Li+

Cation Exchagne Capacity
CEC mass of exchangeable cation adsorbed per unit mass of soil
cmolc/kg soil
Charge for charge basis – NOT ion for ion
1 cmol Na+ = ½ cmol Ca2+ = 1/3 cmol Al3+
pH dependent
Lab Exercise for quantification of CEC

Content Video G

CEC – Soil Order

https://gotoclass.tnecampus.org/d2l/common/dialogs/quickLink/quickLink.d2l?ou=8094442&type=content&rcode=TBR-23959783

2/21/2020 Soil Colloids (Chapter 8) Notes – AGRI1050R50: Introduction to Soil Science (2020S)

https://gotoclass.tnecampus.org/d2l/le/content/8094442/viewContent/60403389/View 10/12

Soil Solution – Plant Uptake
Vary with climate:
Humid/Wet/Warm/Acidic pH: Ca2+, Al3+, Al(OH)x, H+
Less Wet/Neutral pH: Ca2+, Mg2+, Na+

Soil Cations – Plant Nutrition

2/21/2020 Soil Colloids (Chapter 8) Notes – AGRI1050R50: Introduction to Soil Science (2020S)

https://gotoclass.tnecampus.org/d2l/le/content/8094442/viewContent/60403389/View 11/12

Anion Exchange
CEC majority of ion exchange
Opposite of CEC
Negatively charged anions – satisfy positive charge
Sulfate, Nitrate, Phosphate
Inner-sphere complex
Less plant available, but less leaching loss

Weathering, Clays, CEC

Content Video H

Sorption
Sorption – adsorption + absorption
Soil – Bind pesticides – Slow down leaching
Kd = { (mg chemical sorbed/kg soil) / (mg chemical/L solution) }
Koc = { (mg chemical sorbed/kg organic carbon) / (mg chemical/L solution) }
Higher Kd or Koc – more tightly bound
Management strategy – hi or low

https://gotoclass.tnecampus.org/d2l/common/dialogs/quickLink/quickLink.d2l?ou=8094442&type=content&rcode=TBR-23959785

2/21/2020 Soil Colloids (Chapter 8) Notes – AGRI1050R50: Introduction to Soil Science (2020S)

https://gotoclass.tnecampus.org/d2l/le/content/8094442/viewContent/60403389/View 12/12

Reflect in ePortfolio Download Print

Biomolecules and Soil Colloids

Task: View this topic

Activity Details

https://gotoclass.tnecampus.org/d2l/le/content/8094442/navigateContent/176/Previous?pId=60403304

https://gotoclass.tnecampus.org/d2l/le/content/8094442/navigateContent/176/Next?pId=60403304

javascript:void(0);