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3/19/2020 Soil Alkalinity, Salinity, Sodicity (Chapter 10) Notes - AGRI1050R50: Introduction to Soil Science (2020S)

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Soil Alkalinity, Salinity, Sodicity (Chapter 10) Notes

Soil Alkalinity, Salinity, Sodicity (Chapter 10) Notes

Did you know .... Did you know that even in the desert plants can grow and thrive? Chapter 10 highlights soil alkalinity, salinity, and sodicity. Soil in these catergories tend to be very dry, but with property management can be productive and even support the growth of plants and animals.

Lecture content notes are accompanied by videos listed below the notes in each submodule (e.g. Alkalinity, Salinity, Sodicity (Chapter 10) 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 referenced are from the course text, Nature and Property of Soils, 14th Edition, Brady and Weil.

Content Video A

Soil Alkalinity, Sodicity, Sodicity

Characteristics DRY Soils < 500 mm Rainfall Aridisols and Entisols

AGRI1050R50: Introduction to Soil Science (2020S) LH

3/19/2020 Soil Alkalinity, Salinity, Sodicity (Chapter 10) Notes - AGRI1050R50: Introduction to Soil Science (2020S)

https://gotoclass.tnecampus.org/d2l/le/content/8094442/viewContent/60403404/View 2/6

Aridisols and Entisols Alkaline: pH >7 Salts Islands of Fertility Desert Pavement Calcium Carbonate Accumulation – Calcic Horizon

Content Video B

Sources of Alkalinity Alkaline vs Alkalinity

Alkaline: Soils with pH >7 Alkalinity: Concentration of OH-

OH- Producers - Carbonates CO32- and HCO3-

Ion on Exchange: Ca2+ on exchange:

Less water-soluble, ppt CO3 pH 7 to 8.4 - Tolerable

Na+ on exchange: More water soluble, More OH- pH > 8.4 – Toxic

! Salt Accumulation !

3/19/2020 Soil Alkalinity, Salinity, Sodicity (Chapter 10) Notes - AGRI1050R50: Introduction to Soil Science (2020S)

https://gotoclass.tnecampus.org/d2l/le/content/8094442/viewContent/60403404/View 3/6

Salt-affected Soils

Irrigation and Salinity Salt Irrigation Water – Man Inducted Issues

Water – Naturally High in Salts High Temps – High Evaporation Rates Need even more water for crop production Water Evaporates – Salts Left Behind Perpetuates natural salt concentrations

Sodic Soils – Na+ on exchange Sites Salinity – Salt affects crop production Worldwide Issue – Food Production

Content Video C

Measuring Salinity/Sodicity TDS: Total Dissolved Solids

Basic Test All salt solids in solution: mg/L

EC: Electric Conductivity More salts, more conductivity Lab or Field

3/19/2020 Soil Alkalinity, Salinity, Sodicity (Chapter 10) Notes - AGRI1050R50: Introduction to Soil Science (2020S)

https://gotoclass.tnecampus.org/d2l/le/content/8094442/viewContent/60403404/View 4/6

deciSiemens per meter (DS/m) Sodium ESP: Exchangeable Sodium Percentage

Percent Na+ of CEC SAR: Sodium Adsorption Ratio

Considers Ca2+ and Mg2+ SAR lower than ESP

Estimating Soil Salinity

Classification Salinization: Process of accumulating salts

Saline Soils: Starting to accumulate salts ECe > 4 dS/m SAR < 13 pH < 8.5

Saline-Sodic Soils: Intermediate accumulation ECe > 4 dS/m SAR > 13 Plant issues begin

Sodic Soils: Na+ on Exchange ECe < 4 dS/m SAR > 13 pH > 8.5 Soils disperse – Hard for plants to survive

3/19/2020 Soil Alkalinity, Salinity, Sodicity (Chapter 10) Notes - AGRI1050R50: Introduction to Soil Science (2020S)

https://gotoclass.tnecampus.org/d2l/le/content/8094442/viewContent/60403404/View 5/6

Degradation – Soil Dispersion Na+ is the issue

Hydrated Na+ ions large, takes double to satisfy charge Too large and too many between colloids for flocculation Disperse – Break Apart Infiltration low – puddles - no soil structure

Ca2+ or Mg2+ on exchange sites: Smaller radii, cohesive forces, flocculation Improved infiltration rates and gas exchange

Content Video D

Salt Tolerance of Plants

Reclaiming Salty Soils Leach salts out of the profile! Sodic Soils:

Add Gypsum – CaSO4 Move Ca2+ onto colloids Na2SO4 ppt/leached Increases soil structure Better infiltration

3/19/2020 Soil Alkalinity, Salinity, Sodicity (Chapter 10) Notes - AGRI1050R50: Introduction to Soil Science (2020S)

https://gotoclass.tnecampus.org/d2l/le/content/8094442/viewContent/60403404/View 6/6

Reflect in ePortfolio Download Print

Increases soil structure - Better infiltration Plants – Promote soil structure

Continued management: Irrigation Water SAR, EC, etc. Soil Amendments

Review Name some characteristics of dry soils? Pros/Cons of islands of fertility and desert pavement Why is CEC generally greater on soils in arid regions? Micronutrients generally more or less available in alkaline soils? Main micronutrient with issues on alkaline soils? Sources of alkalinity Why is it important to know which ion is most prominent on the exchange sites?? Why does irrigation in arid regions cause soil salinity? Do you know the common methods measuring soil salinity and their units of measure? Difference between saline and sodic? Dispersion – why does it happen, ion is issue? What are some means of reclaiming saline and sodic soils?

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