Exchangeable Acidity & Aluminum
Reagents
In 10 l carboy (enough for 65 samples)
- 745.9 g Potassium Chloride (1 M KCl)
- Bring to volume with DI water.
In 1 l volumetric flask (enough for 100 samples)
- 58.1 g Potassium Fluoride (1 M KF)
- Bring to volume with DI water.
- Phenolpthalein indicator
- Sodium Hydroxide Standard (1N NaOH)
- Hydrochloric acid Standard (1N HCl)
Procedure
Add the following to 125 ml sample cup
- 10 g Oven-dried equivalent, sieved soil (can be field fresh)
- 75 ml Potassium Chloride (1 M KCl)
Place on orbital shaker (200 rpm) for 30 minutes.
Filter suspension (coarse filter paper) in a plastic funnel into a 250 ml Erlenmeyer flask
Wash soil THREE successive 25 ml aliquots of KCl for a total of 150 ml per sample.
Add five drops of Phenolpthalein indicator.
Stir constantly with a magnetic stir plate.
Titrate the solution with 1 N NaOH (or 0.1 N) using a titrating electronic pipette (accuracy 5 碌l).
Note the volume to a permanent pink end-point for KCl-exchangeable total acidity.
Repeat this procedure with 150 ml of 1M KCl (accounts for acidity in KCl).
Add 10 ml of 1 M KF & swirl to mix. (Solution should become dark pink.)
Titrate the solution with 1 N HCl (or 0.1 N) using a titrating electronic pipette (accuracy 5 碌l).
Note the volume to a permanent clear end-point for KCl-exchangeable Al3+.
Adapted from Sims JT. (1996) Lime Requirement. Methods of soil Analysis. Part 3. Chemical Methods-SSSA Book Series no. 5.
Created: 08/01/07 Revised: 10/10/11