Nitrous Oxide Emissions from Cotton Fertilized with Urea Ammonium Nitrate.

The effects of the anthropogenic increase in atmospheric greenhouse gases (GHGs) concentration on climate change are beyond dispute. Of the three biogenic GHGs (i.e., carbon dioxide (CO₂), methane (CH₄) and nitrous oxide (N₂O)), N₂O is considered to be the most potent. It has been estimated that in California, agricultural soils accounts for 50% of the total N₂O emissions. California’s San Joaquin Valley is among the major producers of cotton in the United States. The overall goal of this study was to determine detailed time series of N₂O fluxes at crucial management events, for two cotton crops in the Central Valley of California. For Site A, the objective was to determine N₂O fluxes for cotton from beds and furrows and for Site B, the objective was to determine N₂O emissions for cotton fertilized with different rates Urea Ammonium Nitrate combined with Nutrisphere-N (NSN). Flux chamber measurements were conducted using an EPA approved methodology to collect air samples which were ultimately analyzed using a Gas Chromatograph. The primary findings indicate that the N₂O flux was highest when irrigation was applied after fertilizer application. At Site A, total N₂O fluxes from furrows were 64% lower than that from the beds and the emission factor for beds was 0.69%. At Site B, the emission factor for 50, 100 and 150 lbs N/acre applied with NSN was 0.01, 0.29 and 0.38% respectively, whereas for the same treatments without application of inhibitor was 0.34, 0.32 and 0.20% respectively. Therefore, the study indicates that the NSN has a tendency to reduce the N₂O emissions when fertilizer rate is lower than 100 lbs N/acre.