Methane emission from irrigated rice ecosystem: relationship with carbon fixation, partitioning and soil carbon storage

Rice is a major agricultural crop and accounts for 40 % of the total food grain production of India. A field experiment was conducted for two successive seasons (December-June, 2012-13 and December-June, 2013-14) to assess the efficiency of rice varieties for methane (CH4) emission in relation to atmospheric carbon fixation, partitioning of carbon, and storage in the soil. Six high yielding rice varieties, Bahadur, Cauvery, Dinanath, Joymoti, Kanaklata, and Swarnabh were grown under irrigated condition. Results of the present investigation depicted differences in photosynthetic rate among the varieties accompanied by differential ability for plant biomass partitioning between the shoots and the roots. Stomatal frequency of flag leaf at panicle initiation stage was found to have strong influence on photosynthesis. Low CH4-emitting rice varieties, Bahadur and Dinanath, were found to have lower size of the xylem vessels than the high CH4-emitting rice varieties, Joymoti and Kanaklata, and found to influence the CH4 flux. Soil organic carbon storage of 0.505 Mg C ha(-1) y(-1) in the plough layer of soil (0-15 cm) confirmed that irrigated rice ecosystem is an effective sink of carbon. These findings suggest that selection of suitable rice varieties with higher photosynthetic efficiency and lower emission of CH4 can be a suitable biological mitigation of this greenhouse gas. Although an inverse relationship of CH4 with carbon dioxide (CO2) efflux was observed, irrigated rice ecosystem has a good potential to store substantial amount of carbon in the soil.