Examine why flooded rice ecosystems are disproportionately large sources of methane compared to other agricultural systems, and assess India's exposure given its cropping geography.

Q. Examine why flooded rice ecosystems are disproportionately large sources of methane compared to other agricultural systems, and assess India's exposure given its cropping geography. (15 marks, 250-350 words)

Rice is the only major cereal grown in standing water, and that single agronomic fact makes it a climate outlier: methane constituted about 97% of the CO₂-equivalent warming from rice fields measured in Eastern India [2]. India's cropping geography magnifies this exposure.

Why flooded paddies emit disproportionate methane - Anaerobic soil chemistry: continuous ponding blocks oxygen diffusion, allowing methanogenic microbes to dominate decomposition. The proportion of the season a field stays flooded is the single strongest predictor of methane output [2]. - Plant as chimney: rice aerenchyma vent soil-borne methane directly to the atmosphere, bypassing oxidation at the soil surface. - Substrate loading: intensified straw/residue incorporation into flooded soils feeds methanogens; with area expansion, this drove a doubling of global paddy GHG emissions since the 1960s — soil CH₄ up 44%, soil CO₂ up 52% [1]. - Sink turned source: over one-third of paddy area has flipped from carbon sink to net source through soil organic carbon loss [1]. - By contrast, dryland cereals stay aerobic; their footprint is N₂O- and energy-dominated, not methane-dominated.

India's exposure - Scale: as the world's largest rice producer, India's fields rank among the world's top methane sources, with paddy covering 55% of rainfed harvested area [3]. - Hotspot geography: the Eastern Gangetic Plain is flagged as a global methane hotspot [3]; monsoon-driven deep flooding pushed emissions to ~297 kg CH₄/ha in a wet year against 121 kg in a dry year [2]. - Intensification risk: expanding irrigation, residue incorporation and rising nitrogen use all push emissions upward [1]. - Tempering factor: continuously flooded fields are a minority in the Eastern Gangetic Plains, so hydrology is heterogeneous and uniform prescriptions may misfire [2].

India's exposure is therefore structural but tractable. Region-specific water management — Alternate Wetting and Drying (30–50% methane cut), SRI and Direct Seeded Rice under the National Mission for Sustainable Agriculture [4] — plus optimised residue and nitrogen use can cut net emissions by roughly 10% without yield loss [1]. Aligning paddy agronomy with India's NDC thus protects both food security and climate credibility.

(~330 words)

Sources: 1. Global rice paddy greenhouse gas emissions have doubled over the past six decades driven by area expansion and intensified residue incorporation — Nature Food (2026) — doubling of paddy GHGs, 44% CH₄ / 52% CO₂ rise, sink-to-source flip, residue and nitrogen drivers, ~10% mitigation without yield loss 2. Hydrologic variability governs GHG emissions in rice-based cropping systems of Eastern India — PMC — methane ~97% of CO₂-e, flooding duration as chief predictor, 297 vs 121 kg CH₄/ha wet–dry years, heterogeneous field hydrology 3. India's rice fields rank among world's top methane sources — The Hindu (26 July 2026) — India's rank, 55% of rainfed harvested area under paddy, Eastern India as global methane hotspot 4. Measures to Reduce Methane Emissions — PIB, Ministry of Agriculture & Farmers Welfare — AWD, SRI and DSR as mitigation practices under the National Mission for Sustainable Agriculture