Nitrous oxide emissions from Chinese cropland fertilized with a range of slow-release nitrogen compounds

The consumption of synthetic nitrogen fertilizer in agriculture has increased over the past several decades and will continue to increase to meet the food and fibre demands of the growing global population, which will no doubt result in the release of additional N2O into the atmosphere. A wise use of synthetic fertilizer N is important to mitigate N2O emissions. Outdoor pot experiments during the winter wheat (Triticum aestivum L.) growing season and field experiments during the maize (Zea mays L.) growing seasons were undertaken from 2006 to 2008 at Nanjing in eastern China to evaluate the potential of a range of typical slow-release fertilizers to mitigate N2O emissions. Five slow-release N fertilizers, including physically altered (Ca-Mg-P-coated urea, polymer-coated urea and sulfur-coated urea), chemically altered (urea formaldehyde) and biochemically inhibited (urea with dicyandiamide and hydroquinone) nitrogen were applied in this experiment. In comparison with commercial urea, the urea formaldehyde treatment reduced N2O emissions by ∼42% for the wheat growing season and 15-26% for the maize growing season, and the urea with dicyandiamide and hydroquinone treatment reduced N2O emissions by 33-63% for the maize growing season. However, the treatments with Ca-Mg-P-coated urea, polymer-coated urea and sulfur-coated urea generally enhanced N2O emissions in comparison to the emissions of the urea-treated fertilizer, especially when precipitation followed application. We conclude that the application of chemically altered or biochemically inhibited nitrogen fertilizers would have great potential to mitigate N2O emissions, but the use of physically altered nitrogen fertilizers may have the opposite effect than desired.