Environmental and economic opportunities of applications of different types and application methods of chemical fertilizer in rice paddy

Mitigating greenhouse gas (GHG: Methane and nitrous oxide) emission from the rice cropland vis-A-vis increasing rice yield is one of the important challenges to the food security and climate change research. N-fertilizer input to the crop land is the key to rice productivity and GHG emission from soil. The sustainability of different types and application methods of N-fertilizers in rice cropland was studies based on the net annual C-equivalent GHG emission (CE) and total financial profit to the farmers'. The study was conducted in a low lying experimental rice field of eastern India during two consecutive years. The experiment was laid down with five replicates of the following treatments: (1) control (no N-fertilizer); (2) broadcasting ammonium sulphate (AS); (3) prilled urea (PU) and (4) deep placement of urea briquette (UB). Compared to other treatments, significantly higher GHG emission and grain yield (5-20% higher over other fertilizer applied plots) were recorded from the PU and UB applied plots respectively. Net CE was calculated using the GHG emission and secondary CE of different processes used in each treatment. The net CE followed the order: PU > UB > Control > AS. The ratio of total grain-C to net CE was significantly higher from the AS (15-51%) and UB (8-34%) plots compared to the PU applied plots. Net financial benefit ($ ha(-1)) to the farmers' followed the order: UB > AS > Control > PU. Study indicates that UB may be a climatically sustainable mitigation option in the tropical rice paddy.