Page 54 - Agriculture_Form_Three

Agriculture for Secondary Schools

Readout digital scale
Sensing electrode

Readout analog scale

Switch button

Sensing electrode

Figure 2.3 (a): Analogue soil pH metre Figure 2.3 (b): Digital soil pH metre

Materials needed
50 -100 ml graduated water bottle with a cap, a measuring scoop (a tablespoon/
teaspoon), pH metre, calibration solutions or buffer solution (a solution of pH 4 and
7), wash bottle, distilled water, and air-dried soil
Procedures
(i) Place a table teaspoon full of air-dried soil (if the measuring scale is present,
measure a 20 g sample of soil) into the water bottle.
(ii) Add 40 ml of distilled water.
(iii) With the bottle cap on, shake the soil solution vigorously by hand for a minute.
(iv) Wait 20 to 30 minutes for the solution to settle.
(v) Calibrate the soil pH metre according to maker’s instructions and this should be
done always.
(vi) Measure the pH of the soil solution by inserting pH electrodes into the soil
solution. Make sure that the electrodes are not in direct contact with soil residues
in the water bottle but rather with the supernatant solution. The resulting reading
on the pH metre is the pH of your soil.

Student’
Student’s Book Form Twos Book Form Three
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AGRICULTURE FORM 3 9.11.2022.indd 43
AGRICULTURE FORM 3 9.11.2022.indd 43 10/01/2025 12:31