Page 53 - Agriculture_Form_Three

Agriculture for Secondary Schools

Soil pH test strip method: The pH test strip method uses the same principle as the
universal indicator solution with the exception that with the test strip, the indicator
is not a solution but rather a piece of paper. The method is quick; it does not require
much training and it can quickly determine a soil’s pH in the field. However, the
method only provides soil pH by estimation and may be a limitation if the exact pH
value is needed.

Materials needed
pH paper strips and colour charts, air-dried soil sample, graduated containers (beaker
or a transparent plastic container) or test tube, distilled water, measuring scoop or
teaspoon, and coffee/tea sieve

Procedures
(i) Add 2 tea spoonfuls of air-dried soil into a container.

(ii) Fill the container with distilled water to the same level as the soil sample, stir,
shake or swirl the mixture for a minute.
(iii) Let the solution settle for a minimum of 30 minutes.

(iv) Filter to capture the solid soil particles but allow the liquid to pass through to
the second container.
(v) Insert the paper strip into the solution in the second container.

(vi) After the paper strip has gone through the colour change, match the colour on
the paper strip to the corresponding colour chart. The resultant matching will
give an estimation of that soil’s pH.

Soil pH metre method: This method uses a special device known as soil pH metre.
It consists of a glass electrode that is sensitive to hydrogen ions (H ) which are used
+
to measure the level of acidity (refer to Figures 2.3 (a) and (b)). This method is
accurate and precise. However, the availability of a pH metre in the field may be a
problem in some areas. In addition, the buffer solutions to calibrate the pH metre are
expensive and field work requires frequent calibrations. Moreover, the electrodes
are also fragile and need to be handled with care.

Student’s Book Form Three
42

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AGRICULTURE FORM 3 9.11.2022.indd 42 10/01/2025 12:31