Question 12 from UPSC CSE 2022 - Environme nt

Question

Among the following crops, which one is the most important anthropogenic source of both methane and nitrous oxide?

Accepted Answer

Correct Option: B. Rice

Strategy: The question requires focusing on crops associated with significant greenhouse gas emissions. Among the options, only rice is commonly linked with both methane and nitrous oxide emissions due to waterlogged paddy fields fostering anaerobic conditions. Cotton, wheat, and sugarcane fields do not create these conditions and are not known for high emissions of both gases. Thus, rice is the clear answer.

Key Info: Methane (CH4) and nitrous oxide (N2O) are potent greenhouse gases. Over 20 years, their global warming potentials are estimated at 80-83 times and 273 times greater than CO2, respectively.

Paddy (rice) cultivation, particularly under flooded conditions, creates anaerobic environments. These conditions are conducive to methane production by methanogenic archaea in the soil. Nitrous oxide is also generated from fertilized soils through microbial processes like nitrification and denitrification. Rice paddies are unique because their waterlogged conditions drive methane emissions, while intensive nitrogenous fertilizer use contributes to nitrous oxide release. Rice plants serve as a conduit for these gases from the soil to the atmosphere.

In contrast, upland or well-drained crops such as cotton, wheat, and sugarcane do not contribute comparably to both methane and nitrous oxide emissions. Globally, agriculture is a significant anthropogenic source of these gases, with rice paddies being particularly notable among cereal crops.

### Mitigation Practices for Rice Field GHG Emissions
*   Alternate wetting and drying techniques.
*   Reduced fertilizer use.
*   Improved water management.

Answer

Option A: Cotton

Answer

Option C: Sugarcane

Answer

Option D: Wheat