Question

Which of the following adds/add nitrogen to the soil?

1. Excretion of urea by animals

2. Burning of coal by man

3. Death of vegetation

Select the correct answer using the codes given below.

1. 1 only
2. 2 and 3 only
3. 1 and 3 only
4. 1, 2 and 3

Answer 1

Correct Answer - Option 3 : 1 and 3 only

The correct answer is 1 and 3 only.

• When coal is burnt, nitrogen helps to form oxides which may be released as flue gases and thereby pollute the atmosphere.
  • It does not add nitrogen to the soil unless the oxides so created enter into the nitrogen cycle.
  • Then, what remains after burning coal is Fly Ash.
  • Fly Ash is devoid of nitrogen content.
  • Hence statement 2 is not correct.
• Nitrogenous Waste products of Living organisms such as urea and uric acid and dead remains of organisms are converted back to inorganic ammonia by the bacteria.
  • Hence statements 1 and 3 are correct.

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• Nitrogen Cycle (Gaseous Cycle)
  • Apart from carbon, hydrogen, and oxygen, nitrogen is the most prevalent element in living organisms.
  • Nitrogen is a constituent of amino acids, proteins, hormones, chlorophyll, and many vitamins.
  • Plants compete with microbes for the limited nitrogen that is available in the soil. Thus, nitrogen is a limiting nutrient for both natural and agricultural ecosystems.
  • Nitrogen exists as two nitrogen atoms (N₂) joined by a very strong triple covalent bond (N ≡ N).
  • In nature, lightning and ultraviolet radiation provide enough energy to convert nitrogen to nitrogen oxides (NO, NO₂, N₂O).
  • Industrial combustions, forest fires, automobile exhausts and power-generating stations are also sources of atmospheric nitrogen oxides.​