Question

Why is Cation Exchange Capacity of the soils important in agriculture?

• A. It influences soil color
• B. It affects soil pH
• C. It indicates nutrient-holding capacity
• D. It determines soil structure

Hint:

• CEC is a measure of a soil's ability to hold positively charged nutrients (cations) like calcium, magnesium, and potassium.
• Higher CEC means the soil can retain more of these essential plant nutrients, preventing them from being leached away.
• This makes CEC a key indicator of soil fertility and its capacity to supply nutrients to crops.
• CEC also plays a role in buffering soil pH and influencing the fate of some pollutants.

Answer 1

The Correct Option is C

Cation Exchange Capacity (CEC) is a crucial soil property for agriculture due to several reasons, primarily related to soil fertility and nutrient management:

• Indicates Nutrient-Holding Capacity (option c): This is the most direct and significant importance of CEC. Many essential plant nutrients exist as cations in the soil solution (e.g., Ca$^{2+}$, Mg$^{2+}$, K$^+$, NH$_4^+$). The negatively charged sites on soil colloids (measured by CEC) adsorb these nutrient cations, holding them in a form that is readily available to plants but also protected from being easily leached away by water. A higher CEC generally means a greater capacity to retain these essential nutrients, making the soil potentially more fertile.
• Affects Soil pH (option b): While CEC itself is a measure of charge, the types of cations occupying the exchange sites (particularly H$^+$ and Al$^{3+}$ vs. basic cations like Ca$^{2+}$, Mg$^{2+}$, K$^+$) influence soil pH. Soils with high CEC can also buffer against changes in pH. So, it does affect soil pH, but its role in nutrient holding is more direct when considering "importance in agriculture."
• Influences Fertilizer Requirements: Understanding CEC helps in determining appropriate fertilizer application rates, as it affects how well the soil can retain added nutrients.
• Reduces Leaching of Cations: By holding onto cations, CEC helps prevent their loss from the root zone through leaching, improving nutrient use efficiency.

Option (a) It influences soil color: Soil color is primarily influenced by organic matter content, iron oxides, and moisture content, not directly by CEC. Option (d) It determines soil structure: Soil structure is influenced by factors like soil texture (sand, silt, clay content), organic matter, and biological activity. While clay and organic matter (which contribute to CEC) also influence structure, CEC itself is a chemical property related to charge, not a direct determinant of physical structure in the way aggregation is. The most significant agricultural importance of CEC is its role as an indicator of the soil's ability to retain and supply essential nutrient cations to plants. \[ \boxed{\text{It indicates nutrient-holding capacity}} \]