Standard buffer solutions for calibrating pH meter, usually pH 4.0 and pH 7.0. Calibrate the pH meter over the appropriate range using the standard buffers. See Chapter 2 for details on soil sample preparation and scooping technique. Add 5 mL distilled or deionized water to the sample. Stir vigorously for 15 seconds and let stand for 30 minutes.
Place electrodes in the slurry, swirl carefully, and read the pH immediately.
Ensure that the electrode tips are in the slurry and not in the overlying solution. For the CaCl 2 pH measurement, add 1 drop of 1.0 M CaCl 2 solution to the previous sample. Alternatively, prepare a sample as was done in steps 2 and 3, using 0.01 M CaCl 2 instead of water. Stir vigorously and let stand for 30 minutes, stirring occasionally. Read the pH as in step 5.