EQUIPMENT

  1. Digital pH meter
  2. Combination pH electrode

REAGENTS

  1. Potassium Chloride: KCl
  2. Potassium Hydroxide: KOH
  3. p-Nitrophenol: HOC6H4NO2
  4. Boric Acid: H3BO4

ADAMS-EVANS BUFFER

  1. Weigh 444 g potassium chloride into a 6 liter flask containing 4500 mL deionized water. Stir until dissolved.
  2. Add 63 g potassium hydroxide and stir until dissolved.
  3. Add 120 g p-nitrophenol and continue to stir.
  4. Add 90 g boric acid.
  5. Place the flask on a stirring hot plate and heat and stir until dissolved.
  6. Cool, dilute to 6 liters with deionized water and mix well.
  7. Adjust the pH to 8.00 with KOH of HCl as needed.

PROCEDURE

  1. If the water pH is less than 6.0, add 20 mL of Adams-Evans buffer to the cup containing 20 mL soil + 20 mL deionized water.
  2. Regardless of the water pH, add 20 mL of Adams-Evans buffer to the check soil cup.
  3. Shake for 10 minutes in a shaker box at low speed (200 oscillations per minute)
  4. Adjust pH meter to read 8.00 on a diluted Adams-Evans buffer (20 mL buffer + 20 mL deionized water)
  5. Immerse the combination electrode in the buffered soil suspension and read the buffer pH.
  6. Record the result to the nearest 0.05 pH unit.

QUALITY CONTROL

  1. Buffer pH values on the check soil must be within 0.15 pH units of the established buffer pH for this soil.

LIME REQUIREMENT

  1. The lime requirement is calculated based on an equation using the water pH and the buffer pH.

EXCHANGEABLE HYDROGEN

Exchangeable H is determined using the following equation:

(8.00-buffer pH) × 8 = milliequivalents H/100 grams soil

REFERENCES

  1. Adams, F. and C. E. Evans. 1962. A Rapid Method of Measuring Lime Requirement of Red-Yellow Podzolic Soils. Soil Sci. Soc. Amer. Proc. 26(4): 355-357.
  2. Hajek, B. F., F. Adams, and J. T. Cope. 1972. Rapid Determination of Exchangeable Bases, Acidity, and Base Saturation for Soil Characterization. Soil Sci. Soc. Amer. Proc. 36: 436-438.