Emissions of nitrous oxide, nitrogen oxides and ammonia from a maize field in the North China Plain

The exchange fluxes of nitrous oxide (N2O), nitrogen oxides (NOx) and ammonia (NH3) from a maize field with three different treatments were simultaneously measured using static and dynamic chambers in the North China Plain (NCP) from June 28 to October 11, 2009. The three treatments included control plot (CK, without crop, fertilization and irrigation), fertilizer N plot (NP) and wheat straw returning plus fertilizer N plot (SN). N-fertilizer application greatly stimulated the emissions of N2O, NOx and NH3, with durations of about 10 days for N2O and NO, and about 7 days for NH3. Fertilizer loss rates were 1.08% (NP plot) and 1.20% (SN plot) as N2O–N, were 1.93% (NP plot) and 0.76% (SN plot) as NO–N, and were 5.24% (NP plot) and 3.03% (SN plot) as NH3–N. In comparison with the NP plot, the significant low fertilizer loss rates as NO–N and NH3–N from the SN plot indicated that the wheat straw returning to the field could reduce NOx and NH3 emissions. The molar ratio of NO/N2O was greater than unity for most data during the pulse emission periods induced by fertilization, and thus, nitrification was the dominant process for N2O and NO emissions during these periods. Considering the significant amount (>80%) of N2O and NOx emissions occurred during the pulse emission periods, the emissions of NOx and N2O from the investigated field were mainly ascribed to nitrification process.