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Soil Reaction

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

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Soil Reaction

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  1. 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+)

  2. Soil Reaction • Types of Soil Reaction • Actual Soil Reaction → Active Reaction pHH2O • Potential Soil Reaction →exchangeable soil reactionpHKCl,E.A. → Hydrolytic acidity Ha Ability of soil to change pH of hydrolytically fissile salt solutions

  3. Soil Reaction • Methodology of pHKCl a E.A. determination (exchangeable soil reaction) • Weight 40g of soil + 100ml 1M KCl • Let the soil with KCl shake for 45min. • Measure the pHKClvalue by the pH-meter pHKClEvaluation Strongly Acid< 4.5 Acid 4.5 – 5.5 Weakly Acid 5.5 – 6.5 Neutral 6.5 – 7.2 Alkaline>7.2

  4. Soil Reaction • Methodology of pHH2O determination • Weight 10g of soil + 20ml overcooked distilled water • Mix the soil and water for 5min using the glass straw • Measure pHH2Ovalue 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

  5. Soil Reaction 0 Acid sulphate soils Forest Soils Cultivated soils of temperate zone Calcareous soils Solonchaks

  6. Soil Reaction • The specifics of the measurement of soil reaction • The measurement takes place in soil suspension (not in soil solution) H3O+ Soil Particles SOLUTION SUSPENSION

  7. Soil Reaction • Types of Soil Reaction • Actual Soil Reaction → Active Reaction Concentration of H3O+ ions in soil suspension pHH2O H3O+ Soil Particles Water

  8. Soil Reaction • Types of Soil Reaction • Potential Soil Reaction → exchangeable soil reaction Ability of soil to change pH of neutral salt solutions pHKCl E.A. H3O+ Soil Particles KCl solution K+

  9. Soil Reaction • Types of Soil Reaction • Actual Soil Reaction → Active Reaction pHH2O • Potential Soil Reaction →exchangeable soil reactionpHKCl,E.A. → Hydrolytic acidity Ha Ability of soil to change pH of hydrolytically fissile salt solutions

  10. Soil Reaction • Soil Reaction Measurement • Colorimetrically (Color indicators) • Titration • Potentiometrically (Specific and comparative glass calomel electrode)

  11. Soil Reaction • 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+

  12. Soil Reaction • 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, thelower soil pH)

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