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Agriculture for Secondary Schools
Cation Exchange Cations and
anions in solution
Mg 2+
Ca 2+
H + NO 3 -
Na + 2+ Ca 2+
K + Ca +
K + Na
H + Mg 2+ Mg 2+
K + H + K +
Al 3+
Na + Cl -
Ca 2+
Negatively
charged colloid Adsorbed cations
Figure 2.1 (a): Simplified representation of cation exchange between soil solution and a
colloidal particle
Root A negatively charged particle binds cations
hair
Negatively
charged colloid
H + K + K + Ca 2+
H + K + Mg K +
2+
H + K + Mineral cations
CO 2 Ca 2+ are released into
K + H + the soil solution
Mg 2+ K +
CO +H O H CO HCO +H +
-
2 2 2 3 3
The cations are exchanged for hydrogen ions
obtained from carbonic acid (H CO ) or from
2
3
the plant
Figure 2.1 (b): Cation exchange in soil and uptake of mineral nutrients by plants
Student’s Book Form Three
34
10/01/2025 12:31
AGRICULTURE FORM 3 9.11.2022.indd 34 10/01/2025 12:31
AGRICULTURE FORM 3 9.11.2022.indd 34
