Among the following crops, which one is the most important anthropogenic source of both methane and nitrous oxide?
- Cotton
- Rice
- Sugarcane
- Wheat
Explanation
Option (b) is the correct answer
- Rice cultivation is a major contributor to global greenhouse gas emissions, particularly methane (CH₄) and nitrous oxide (N₂O). These emissions arise from the traditional practices of flooding rice paddies and the burning of rice straw and stubble.
- Methane Emissions from Rice Cultivation: Rice paddies are typically flooded during growth, creating anaerobic conditions that lead to the generation of methane by methanogenic bacteria. Methane is a potent greenhouse gas with a global warming potential (GWP) significantly higher than carbon dioxide. It is estimated that rice cultivation contributes approximately 36 million metric tons of methane annually, accounting for 2.5% of radiative forcing.
- Nitrous Oxide Emissions: Nitrous oxide, another potent greenhouse gas, is primarily emitted from rice fields where water levels are intermittently managed. Alternate wetting and drying (AWD) is a technique used to reduce methane emissions by allowing the fields to dry out between irrigation cycles. However, this practice can increase nitrous oxide emissions, as the aeration of the soil during drying periods enhances microbial activity that produces nitrous oxide. Nitrous oxide has a GWP greater than carbon dioxide and a much longer atmospheric lifetime, making it a significant contributor to climate change.
