4B2 pH of 1:5 soil/0.01 M calcium chloride extract – following method 4A1 (without stirring during measurement)

This method provides a convenient laboratory procedure when there is a requirement to report soil pH values from both water and 0.01 M CaCl₂. There should be no significant difference between results obtained by this method and results obtained by Method 4B1.

Reagent

0.21 M Calcium Chloride

Dissolve 30.873 g calcium chloride dihydrate (CaCl₂.2H₂O) and make to 1.0 L with deionised water.

pH Buffer Solutions

pH buffer solutions are as described for Method 4A1.

Procedure

Standardise the pH meter as described in Method 4A1.

Following determination of pH in water (Method 4A1), pipette/dispense 5 mL 0.21 M CaCl₂ solution to 100 mL of the soil suspension to obtain a 0.01 M CaCl₂ solution. Intermittently shake manually or mechanically for 15 min to equilibrate the CaCl₂ solution. Allow the suspension to settle for 20–30 min, position the electrodes in the unstirred supernatant, and record the pH value when a stable reading is obtained. All pH measurements should be completed on the same day, ideally within 4–6 h.

Report pH (1:5 soil/0.01 M CaCl₂) on an air-dry basis.