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Fully outline the role of lime in cation exchange. - Leaving Cert Agricultural Science - Question f - 2014
Question f
Fully outline the role of lime in cation exchange.
Worked Solution & Example Answer:Fully outline the role of lime in cation exchange. - Leaving Cert Agricultural Science - Question f - 2014
Step 1
Cation Exchange Process
Answer
Lime, primarily composed of calcium oxide (CaO) or calcium carbonate (CaCO3), plays a pivotal role in cation exchange in soil. When lime is added to soil, it dissociates into calcium ions (Ca²⁺) which enter the soil solution and contribute to the cation exchange process.
Step 2
Replacement of Cations
Answer
The calcium ions in the soil solution can swap places with other cations, such as hydrogen (H⁺), potassium (K⁺), or aluminum (Al³⁺), that are present on the surfaces of colloids (such as organic matter or clay). This replacement is essential as it influences soil fertility and nutrient availability.
Step 3
Effect on Soil pH and Colloidal Charge
Answer
The replacement of H⁺ ions, which contribute to soil acidity, with Ca²⁺ ions raises the pH of the soil, making it less acidic. Additionally, since many colloids carry a negative charge, the increased presence of calcium can enhance soil structure and stability, promoting better water retention and root penetration.