Question

Nitrogen is an essential nutrient for plant growth. But farmers who cultivate pulse crops like green gram, bengal gram, black gram, etc. do not add nitrogenous fertilisers to the crops. Why?

• A. These plants produce manure for themselves.
• B. These plants make more nitrogen internally.
• C. Nitrogen is harmful for these plants.
• D. The bacteria present in the roots fix nitrogen.

Answer 1

The correct option is (D):

Explanation of the correct option:

1. ​Pulses are a type of leguminous plant.
   
2. Roots of pulses (leguminous plants) have a symbiotic association with a bacterium called Rhizobium which fixes atmospheric nitrogen into the soil.
3. Adding more nitrogenous fertilizers make the level of nitrogen excess in the soil.
4. Hence, farmers need not use nitrogenous fertilizers.
   

Explanation of the incorrect options:

Option (A):

1. ​The plants do not produce green manure themselves as they get that directly from the symbiotic bacteria in the soil.
   

Option (B):

1. The insectivorous plants get their nitrogen digesting the insects and other animals.
   
2. But the plants do not produce nitrogen internally as they need to take up nitrogen from the soil.
   

Option (C):

1. ​Nitrogen is essential to all plants and hence it is never harmful while cultivating pulses.
   

Final Answer: The farmers do not add nitrogen to the soil for cultivating gram seeds because the bacteria present in the roots fix nitrogen.