To study effect of timing of topdressing on N 2O emission from wheat fields during the period from the jointing stage till the maturing stage of wheat, a field experiment was conducted to have three topdressing schedules (top-dressing before rain, topdressing during rain and topdressing after rain) in jointing-maturing stage of wheat from 2007 to 2008. Results show that N 2O emission was 37%-67% and 22%-46% less in fields topdressed after rain, than in fields topdressed before rain and during rain, respectively. No significant difference was observed between the treatments in wheat grain yield ( p>0.05). Soil water content was the key factor affecting N 2O emission during that wheat growing season. Topdressing after rain when soil was wet is an appropriate topdressing method, which may decrease N 2O emission significantly in the wheat-growing season with no adverse effect on wheat yield.
