Quantifying Nitrous Oxide and Nitric Oxide Emissions from Rice Soils
Emissions of nitrous oxide (N2O) and nitric oxide (NO) are mainly controlled by water and nitrogen management. Nitrogen fertilizer use based on IPCC estimates results in 1% N2O emission per unit N fertilizer. Water saving irrigation such as alternate wetting and drying (AWD) is reported to reduce global warming potential of rice farming mainly due to reducing methane emissions. However, its impacts on N2O emissions are not year clear. N2O emission could be reduced by efficient N fertilization. Urea deep placement (UDP) is a promising technology that reduces N loss by up to 35 percent and increases rice yield up to 20 percent. To find the mitigation potential of GHG emissions from water and nitrogen management, IFDC has started long term monitoring of N2O and NO emissions using automated continuous measurement system. The experiments are being conducted under greenhouse conditions in Alabama and field conditions in Bangladesh. The monitoring of N2O and NO emissions started in 2012. The treatments comprised of zero N, deep placed urea briquette, and urea broadcasted in 2-3 splits on rice under flooded and AWD conditions and on wheat under aerobic conditions. Results showed that N2O emissions were sporadic and event specific. The fertilizer-induced peak emissions were observed in broadcast urea treatments after 4-7 days of application. But emission peaks were not observed in UDP treatments. Magnitude and emissions rate varied among locations. In addition to fertilizer induced peak (under urea broadcast), significant emissions were observed when field was alternately wet and dry. Mechanisms affecting N2O and NO emissions under flooded, AWD, and fully upland conditions are discussed. The effect of diurnal temperature variation on N2O and NO emission is also presented.