soil reaction
DESCRIPTION
Soil Reaction. Soil reaction is one of the most important soil characteristic s Soil Reaction Expression In units of activity (concentration) of hydronium ions (H 3 O + ) ions – c H3O+ [ mmol (meq) / 100g of soil ] In pH units = -log(c H3O+ ). Soil Reaction. Types of Soil Reaction - PowerPoint PPT PresentationTRANSCRIPT
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Soil Reaction
Soil reaction is one of the most important soil characteristics
Soil Reaction Expression In units of activity (concentration) of
hydronium ions (H3O+) ions – cH3O+
[mmol (meq) / 100g of soil ]
In pH units = -log(cH3O+)
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Types of Soil Reaction
Actual Soil Reaction → Active Reaction pHH2O
Potential Soil Reaction → exchangeable soil reaction pHKCl, E.A.
→ Hydrolytic acidity
Ha Ability of soil to change pH of hydrolytically
fissile salt solutions
Soil Reaction
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Methodology of pHKCl a E.A. determination (exchangeable soil reaction)
Weight 40g of soil + 100ml 1M KCl Let the soil with KCl shake for 45 min. Measure the pHKCl value by the pH-meter
pHKCl Evaluation
Strongly Acid < 4.5
Acid 4.5 – 5.5
Weakly Acid 5.5 – 6.5
Neutral 6.5 – 7.2
Alkaline >7.2
Soil Reaction
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Methodology of pHH2O determination Weight 10g of soil + 20ml overcooked distilled water Mix the soil and water for 5 min using the glass straw Measure pHH2O value by the pH-meter
Strongly Acid < 4.9
Acid 4.9 – 5.9
Weakly Acid 5.9 – 6.9
Neutral 6.9 – 7.1
Slightly alkaline 7.1 – 8.0
Alkaline 8.0 – 9.4
Strongly Alkaline >9.4
Soil Reaction
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Soil Reaction
Acid sulphate soils
Forest Soils
Cultivated soils of temperate zoneCalcareous soils
Solonchaks
0
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The specifics of the measurement of soil reaction
The measurement takes place in soil suspension (not in soil solution)
H3O+
Soil Particles
SOLUTION SUSPENSION
Soil Reaction
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Types of Soil Reaction
Actual Soil Reaction → Active ReactionConcentration of H3O+ ions in soil suspension
H3O+
Soil Particles
Water
pHH2O
Soil Reaction
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Types of Soil Reaction
Potential Soil Reaction → exchangeable soil reactionAbility of soil to change pH of neutral salt solutions
H3O+
Soil Particles
KCl solution
K+
pHKCl
E.A.
Soil Reaction
![Page 9: Soil Reaction](https://reader035.vdocument.in/reader035/viewer/2022081506/56814f89550346895dbd4364/html5/thumbnails/9.jpg)
Types of Soil Reaction
Actual Soil Reaction → Active Reaction pHH2O
Potential Soil Reaction → exchangeable soil reaction pHKCl, E.A.
→ Hydrolytic acidity
Ha Ability of soil to change pH of hydrolytically
fissile salt solutions
Soil Reaction
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Soil Reaction Measurement Colorimetrically (Color indicators) Titration Potentiometrically (Specific and
comparative glass calomel electrode)
Soil Reaction
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Influences on Soil Reaction Measurement The degree of dissociation - (how many groups
capable of dissociation are present on the surface of solid particles)
Kind of Acidity → free H3O+
→ Reserve acidity - hydrolysis of Al3+
Al3+ + H2O → AlOH2+ + H+
AlOH2+ + H2O → Al(OH)2+ + H+
Al(OH)2+ + H2O → Al(OH)3
+ + H+
Soil Reaction
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Influences on Soil Reaction Measurement The degree of dissociation Kind of Acidity → free H3O+
→ hydrolysis of Al3+
Ratio soil : water - (the wider soil : water ratio, the higher measurement error)
Salt content - (salt displaces H+ from the soil sorption complex)
CO2 content - (the higher CO2 content, the lower soil pH)
Soil Reaction