Modified emission and scaling factors for methane and nitrous oxide in rice system of India: A country specific...

Country specific disaggregated emissions and scaling factors for methane (CH₄) and nitrous oxide (N₂O) from rice is necessary to judge the contribution of rice towards global greenhouse gas (GHG) inventories. India being an agrarian country and rice is a staple food grown in 44.6 million ha and contributed 17.5% of Indian agricultural GHGs budget. However, in recent studies often suggested that using IPCC regional scale emission factors (EFs) for India overestimates the emission from rice systems. This overestimation primarily due to the conditions and ecologies rice grown and per hectare consumption of nitrogen fertilizer in India (76.9 kg N ha^-1 year^-1) is much lesser than the other countries. Therefore, nation-specific EFs and scaling factors (SFs) are crucial not only for India but also for other agrarian countries. So, in this study we developed modified baseline emission factor (BEF) and SF_est (Scaling factors based on ecology, water regime, season and soil texture) of methane in rice systems of India by using 271 field data points. The SF_est was modified for 10 specific conditions. The values for SF_est of CH₄ varied from 1 to 0.11, while the BEF for CH₄ was modified to 0.51 having 73 data points. Modified EFs and SF_est in CH₄ could reduce the average deviation from the measured values by 348% (using IPCC-EFs and SFs) to 22% in the rice system in India. On the other hand EFs for N₂O was modified based on 343 measured data. Further for precise estimation a modified empirical model was developed, incorporating soil available nitrogen component as indirect N₂O emissions. Which could able to reduce the deviation from measured values from 37% to 8% in alternate wetting and drying conditions. Therefore, the modified BEF, EFs and SFs could be helpful for getting precise GHGs inventories for India at national level and chalking out the mitigation strategies.