Question

What is the minimum cardinal temperature ($^{\circ}$C) of maize and wheat

• A. 5-7 and 1.0 - 2.5
• B. 10-12 and 5.0 - 5.5
• C. 8-10 and 3.0 - 4.5
• D. 12-15 and 5.0 - 5.5

Hint:

Warm-season crops (C4 like maize, sugarcane, sorghum) have high minimum cardinal temperatures (\(8\text{--}10^{\circ}\text{C}\)).
Cool-season crops (C3 like wheat, barley, peas) can germinate at much lower temperatures (\(3\text{--}5^{\circ}\text{C}\)).

Answer 1

The Correct Option is C

Step 1: Understanding the Concept:
Every crop species has three critical temperatures, known as cardinal temperatures, that govern its growth and development:
1. Minimum cardinal temperature: The lowest temperature at which physiological processes can occur.
Below this point, growth stops completely.
2. Optimum cardinal temperature: The temperature range where the rate of plant growth is fastest and most efficient.
3. Maximum cardinal temperature: The highest temperature above which physiological activity ceases and irreversible heat damage occurs.

Step 2: Detailed Explanation:
Let us analyze the thermal requirements for the two crops:
- Maize (Zea mays): This is a C4 warm-season (Kharif) crop that originated in tropical regions.
It is highly sensitive to cold temperatures and frost.
The minimum cardinal temperature required for seed germination and seedling growth in maize is relatively high, typically ranging between \(8^{\circ}\text{C}\) and \(10^{\circ}\text{C}\).
Below this range, maize seeds remain dormant or rot in the soil.
- Wheat (Triticum aestivum): This is a C3 cool-season (Rabi) crop that is adapted to temperate climates.
It has a significantly lower thermal requirement for growth than maize.
The minimum cardinal temperature at which wheat seeds can germinate and grow is very low, typically between \(3.0^{\circ}\text{C}\) and \(4.5^{\circ}\text{C}\).
This low thermal threshold allows wheat to be grown successfully during the cold winter months in subtropical and temperate regions.
Therefore, the respective minimum cardinal temperatures are \(8\text{--}10^{\circ}\text{C}\) for maize and \(3.0\text{--}4.5^{\circ}\text{C}\) for wheat.

Step 2: Final Answer:
The minimum cardinal temperature range of maize and wheat is 8-10 and 3.0 - 4.5.