Question

The oxygen diffusion rate (ODR) is measured by the method of

• A. Neutron scattering
• B. Gamma-ray attenuation
• C. Platinum microelectrode
• D. Thermocouple psychrometer

Hint:

Oxygen = Electrode.
Just as a root "drags" oxygen, the platinum electrode "drags" electrons.
This method is essential for studying "waterlogging" stress in crops.

Answer 1

The Correct Option is C

Step 1: Understanding the Question:
Oxygen Diffusion Rate (ODR) is a measure of how quickly oxygen can move from the soil air through the water films around plant roots. The question asks for the standard analytical method to measure this.
Detailed Explanation:

• Platinum Microelectrode Method:
This is the most common method for determining ODR in situ.
A small platinum wire (electrode) is inserted into the soil. A constant voltage is applied to the electrode, causing oxygen molecules at the electrode surface to be reduced.
The resulting electrical current is proportional to the rate at which oxygen diffuses from the surrounding soil to the electrode surface. This mimics the behavior of a plant root.

• Critical ODR:
If the ODR falls below a critical level (usually around \( 20 \times 10^{-8} \text{ g cm}^{-2} \text{ min}^{-1} \)), root growth for most plants is severely inhibited due to hypoxia.

• Analyzing other options:
Neutron scattering: Used for measuring soil moisture content (\( \theta_v \)).
Gamma-ray attenuation: Used for measuring soil density or moisture.
Thermocouple psychrometer: Used for measuring soil water potential.

Step 2: Final Answer:
The Platinum microelectrode is the standard instrument used for measuring the oxygen diffusion rate in soil.