Standards
- Buffer solution 4.00 (Fisher # SB101-500)
- Buffer solution 5.00 (Fisher # SB102-500)
- Buffer solution 7.00 (Fisher # SB108-500)
- Deionized (DI) water (503 Porter)
Materials
- pH meter with glass electrode
- 125 ml sample cup
- Graduated cylinder (25 ml) or repipettor
- Orbital shaker
Procedure
Add the following to 125 ml sample cup
- 10 g Oven-dried equivalent, sieved soil (can be air dried or field fresh)
- 20 ml Deionized (DI) water—A 1:1 dilution (10 g soil to 10 ml DI water) is also acceptable. Do not exceed a 1:5 dilution.
Place on orbital shaker (150 rpm) for 30 minutes.
Let stand for 10 minutes to equilibrate with atmospheric CO 2 and then swirl gently.
Calibrate pH meter with pH 4.0, 5.0, and 7.0 buffer solutions.
- Note that buffer solutions are standardized to specific temperatures. You may have to adjust buffer pH when room temperature differs greatly from 25°C.
Insert pH electrode into soil slurry and read the pH after display has stabilized on a calibrated pH meter.
Rinse pH electrode with DI water to remove any soil or organic matter before moving onto next sample. Please do not blot with a tissue (i.e., Kimwipe).
Check calibration after every 15 samples to nearest pH buffer of soil pH. Recalibrate if necessary.
What to Report
- Soil slurry dilution (1:2)
- Water extracted (as opposed to 0.01 CaCl 2 or 1 M KCl solution)
- Air dried or field fresh soil
- pH units to at least 0.1
Created: 01/27/09; Revised: 10/10/11