Page 50 - Agriculture_Form_Three

Agriculture for Secondary Schools

Similarly, a substantial amount of ammonium-nitrogen (NH -N) applied on the
4
surfaces of high pH soils (above 7) is lost through volatilisation. Generally, soil
pH can affect CEC by replacement of cations or anions which are adsorbed on the
colloidal particles with H or OH . In a soil with higher concentration of H , that is,
-
+
+
lower pH or acidic condition, exchangeable cations will be deficient. The opposite
occurs when pH increases.
(d) It aids in determination of type and estimation of the amount of amendments
needed to soil
Soil pH, being an indicator of the degree of acidity or alkalinity, determines type of
amendment to be done to the soil so as to bring about a favourable soil condition
for crop plant growth and microbial activities. Soil pH also gives an estimate of the

amount of those amendments needed.

Determination of soil pH
There are several methods which can be used in determining soil pH. These methods
include vinegar and baking soda test, colour cards method, soil pH test strip method

and soil pH metre method. These methods are elaborated in the following sub-sections.

Vinegar and baking soda test: This method is based on the pH of both vinegar
and baking soda and how they react with materials with a different pH. Vinegar is
acidic and when it comes into contact with an alkaline material, it foams, bubbles
and fizzes. Baking soda is alkaline and when it comes into contact with an acidic
material, it also foams, bubbles and fizzes. The advantage of this method is fast, easy
and could be performed by any person without any technical knowledge of soils or
specific equipment. However, it does not provide the exact or absolute value of soil
pH but an indication of whether the soil is acidic or alkaline. Therefore, the results
obtained by using this method may need to be further confirmed using methods that
are more accurate.

Materials needed

Hand trowel or shovel, container to hold soil (a ceramic cup or anything that can
hold the soil without interfering with the reaction), vinegar (diluted acetic acid),
baking soda (NaHCO ), distilled water, and glass rod
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Procedures
(i) Clear the sampling points from any vegetation or any leaf or root debris.

(ii) Using a hand trowel or shovel, obtain some soil sample from subsoil.
(iii) Remove any plant roots or debris from the soil sample as much as possible.

Student’
Student’s Book Form Twos Book Form Three
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