Question

Which of the following is a key component of Cation Exchange Capacity of the soils?

• A. Nitrate ions
• B. Anions
• C. Exchangeable cations
• D. Soil water content

Hint:

• Cation Exchange Capacity (CEC) is the total capacity of a soil to hold exchangeable cations.
• Soil colloids (clay and organic matter) have negative charges on their surfaces.
• These negative charges attract and hold positively charged ions (cations) like Ca$^{2+}$, Mg$^{2+}$, K$^+$, Na$^+$, H$^+$, Al$^{3+}$. These are the exchangeable cations.
• CEC is a measure of soil fertility and nutrient retention.

Answer 1

The Correct Option is C

To answer the question, let's explore the concept of Cation Exchange Capacity (CEC) in soils and its key components.

1. Understanding the Concepts:

- Cation Exchange Capacity (CEC): Cation exchange capacity is a measure of how well soil can retain and exchange positively charged ions (cations). It is an important property because it affects the soil's ability to hold essential nutrients for plants and its overall fertility. Soils with high CEC can hold more cations, which are essential for plant growth.

- Cations and Anions: Cations are positively charged ions, while anions are negatively charged. The CEC refers to the soil's capacity to retain and exchange cations such as calcium (Ca²⁺), magnesium (Mg²⁺), potassium (K⁺), and sodium (Na⁺).

2. Breakdown of the Given Options:

• Option 1: "Nitrate Ions": Nitrate ions (NO₃^-) are anions, and CEC specifically deals with cations. Nitrate ions are important for soil fertility but are not a key component of CEC.
• Option 2: "Anions": Anions are negatively charged ions, and CEC primarily involves the exchange of cations, not anions. Anion exchange capacity (AEC) is a separate concept.
• Option 3: "Exchangeable Cations": This is the correct answer. Exchangeable cations are the key component of CEC. These are the positively charged ions that can be readily exchanged with other cations in the soil solution. The higher the concentration of exchangeable cations, the higher the CEC of the soil.
• Option 4: "Soil Water Content": While soil water content is important for nutrient transport and plant growth, it is not a key component of CEC. CEC is specifically related to the ability of soil to hold and exchange cations, not its water content.

3. Conclusion:

The key component of Cation Exchange Capacity (CEC) is exchangeable cations, which are the positively charged ions that the soil can exchange with other cations.

Final Answer:

The key component of Cation Exchange Capacity of the soils is exchangeable cations.