Question

The fixation of nitrogen by the rhizobia in the root nodules of pulse crops generally commences at-

• A. 10 days after sowing
• B. 15 days after sowing
• C. 30 days after sowing
• D. 60 days after sowing

Hint:

In pulses, nitrogen fixation starts around 30 days and continues till pod filling stage for maximum benefit.

Answer 1

The Correct Option is C

Step 1: Rhizobia's Function.
Rhizobia are symbiotic bacteria that colonize leguminous plant roots, forming nodules. Within these nodules, they convert atmospheric nitrogen into ammonia, which plants can then use.

Step 2: Nodule Formation Schedule.
- Rhizobia infection occurs 7-10 days post-sowing, following root growth.
- Nodule initiation starts approximately 10-15 days after sowing.
- Significant nitrogen fixation does not commence immediately after infection.
- Active nitrogen fixation is typically observed only after 30 days, when nodules are well-developed.

Step 3: Evaluation of Options.
- (A) 10 days: Premature; nodules are not yet fully formed.
- (B) 15 days: Still early; nodules may be present, but fixation is minimal.
- (C) 30 days: Accurate; nodules are functional and nitrogen fixation is active by this point.
- (D) 60 days: Excessive; fixation begins much earlier.

Step 4: Determination.
Consequently, nitrogen fixation in pulse root nodules generally begins around 30 days after sowing.