Question

Due to their extensive rice cultivation, some regions may be contributing to global warming. To what possible reason/reasons are this attributable?

1. The anaerobic conditions associated with rice cultivation cause the emission of methane.

2. When nitrogen-based fertilizers are used, nitrous oxide is emitted from the cultivated soil.

Which of the statements given above is/are correct?

1. 1 only
2. 2 only
3. Both 1 and 2
4. Neither 1 nor 2

Answer 1

Correct Answer - Option 3 : Both 1 and 2

The correct answer is Both 1 and 2.

• Rice cultivation - Global warming: 
  • Studies reveal that Rice fields are one of the most important sources of methane emission.
  • Since water saturation of soil limits the transport of oxygen into the soil, anaerobic conditions occur in wetland rice fields as a result of soil submergence.
  • The microorganisms undergo a redox reaction in these anaerobic conditions that leads to methanogenesis (the process of methane formation). Hence statement 1 is correct.
  • Under anaerobic conditions, methanogens produce methane from either of the following two methods:
    • the reduction of carbon dioxide with hydrogen
    • from the fermentation of acetate to methane and carbon dioxide.
  • Nitrogen-based fertilizers, which are used to increase the yield, cause the microbes present in the soil to convert nitrogen into a nitrous oxide which is a major greenhouse gas. Hence statement 2 is correct
  • Methane and nitrous oxide are the two greenhouse gases emitted from the rice fields.
  • When methane and nitrous oxide emissions were observed and compared with rice yield and physical changes of rice plants, it was found that drainage during the flowering period could reduce methane emission. It was also observed that nitrous oxide emission was related to the number of drain days rather than the frequency of draining. Fewer drain days can help reduce nitrous oxide emissions.

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• Methane gas:
  • ​It is a colourless, odourless gas and is among the most potent greenhouse gases.
  • Its chemical formula is CH₄ and is the simplest alkane.
• Nitrous oxide gas:
  • ​It is a colourless, non-inflammable gas, commonly known as 'laughing gas'.
  • Its chemical formula is N₂O and is the third most important greenhouse gas causing global warming.