Previous Year Question

Methane (CH₄) is a powerful Greenhouse Gas emitted from Flooded Paddy Fields. In traditional rice cultivation, fields remain flooded for extended periods, reducing oxygen availability in the soil and creating Anaerobic Conditions. Under these conditions, methane is produced during the microbial decomposition of organic matter. This gas absorbs Infrared Radiation in the atmosphere and contributes to the Greenhouse Effect and Global Warming.

Methanogenesis is primarily carried out by Methanogenic Archaea. These microorganisms produce methane by utilizing compounds formed during the decomposition of organic matter in the absence of oxygen. The methane produced reaches the atmosphere through Gas Bubbles, Diffusion, and the air-filled tissues (Aerenchyma) of rice plants. These tissues, present in rice roots and stems, facilitate gas transport under waterlogged conditions.

The Global Warming Potential (GWP) of Methane is considerably greater than that of Carbon Dioxide (CO₂). According to the IPCC Sixth Assessment, the 100-year Global Warming Potential of biogenic methane is approximately 27.2 times that of CO₂. Other major sources of methane include Wetlands, Enteric Fermentation in ruminant livestock, Landfills, and fossil fuel production. In contrast, Nitrogen (N₂) is not a Greenhouse Gas, while Carbon Monoxide (CO) is primarily a toxic air pollutant.

Methane emissions from rice cultivation can be reduced through Alternate Wetting and Drying (AWD). Instead of keeping fields continuously flooded, water is periodically drained to allow oxygen to enter the soil, thereby reducing methane production. According to the International Rice Research Institute (IRRI), this technique can reduce methane emissions by approximately 30–70% under suitable conditions. However, changes in water management must also account for possible Nitrous Oxide (N₂O) emissions.