Nitrous oxide emissions from an apple orchard soil in the semiarid Loess Plateau of China

Nitrous oxide (N₂O) fluxes from an apple orchard soil in the semiarid Loess Plateau of China were measured using static chambers from September 2007 to September 2008. In this study, three sites were selected at distance of 2.5 m (D 2.5), 1.5 m (D 1.5), and 0.5 m (D 0.5) from the apple tree row. Nitrous oxide fluxes followed seasonal pattern, with high N₂O emission rates occurring in the hot-humid summer and low rates in the cold-dry winter. Pulses of N₂O emissions occurred after nitrogen fertilizer application, summer rainfall events, and during freeze-thaw cycles. Annual average N₂O emission rates were the highest at D 0.5 site (48.2 ± 39.9 μg N₂O m⁻² h⁻¹), the lowest at D 2.5 site (31.9 ± 18.2 μg N₂O m⁻² h⁻¹), and intermediate at D1.5 site (36.8 ± 32.2 μg N₂O m⁻² h⁻¹), suggesting that N₂O emissions from the apple orchard soil increased when the chamber location was closer to the apple tree row. This may be due to the fertilization close to roots in hot and humid season. Over one third (37.1%) of the annual N₂O emission occurred in the summer. Annual N₂O emissions from the apple orchard soil averaged to 3.22 kg N₂O ha⁻¹ year⁻¹. Annual emission factor of the apple orchard from the applied fertilizer (uncorrected for background emission) was 0.658%. This value was nearly a half (53%) of the default value provided by the Intergovernmental Panel on Climate Change for the application of synthetic fertilizers to cropland (1.25%). Therefore, the amount of N₂O emissions from the semiarid apple orchard soil could be largely overestimated if no regional-specific factor is used.