Among the following crop fields, the major source of methane in India is:

Concept

Methane is produced when methanogenic microorganisms decompose organic matter under oxygen-poor, anaerobic conditions.

Agricultural methane therefore becomes important where soil remains waterlogged long enough to suppress oxygen and sustain methanogenesis.

Application

Rice paddies are commonly flooded for substantial parts of the crop cycle. The submerged soil becomes anaerobic, and methane formed in the soil can reach the atmosphere through the water, bubbles, and rice plants.

Contrast

• Wheat fields are generally aerated between irrigations, so they do not maintain the same prolonged anaerobic soil environment.

• Sugarcane fields receive irrigation but are not ordinarily maintained as continuously flooded paddies.

• More than one of the above would require at least two listed field types to share the requested status; the standard classification identifies one specific field type.

• None of the above would require every listed field type to be excluded; the standard classification includes one of them.

Cross-check

Greenhouse-gas inventories classify rice cultivation as a distinct methane-emission source, which matches the flooded-soil mechanism.

For this BPSC paper, the official final answer key identifies rice field, which is consistent with the flooded-soil mechanism.

Therefore, the answer is rice field.