Nitrous oxide emissions from cultivated soils in the North China Plain

Using an enclosed chamber technique, N₂O emissions from intensively cultivated soils in the North China Plain were measured during periods from October 1995 to September 1996 and June 1997 to June 1998, to reflect distinct contributions of the winter wheat and summer maize growing seasons. The results show that the measured annual mean emission of N₂O from soils treated with chemical N fertilizer and from soils treated with chemical N fertilizer combined with organic manure were 52.8 and 61.4 mg N₂O m⁻² h⁻¹, respectively. These emissions from fertilized soils were significantly higher right after the chemical fertilizer was applied. A relatively low annual mean emission of 2.2 μg N₂O m⁻² h⁻¹ was measured in soils that had not been fertilized for 12 years. Maximal annual emissions of N₂O from the studied agroecosystem were 3.9 kg N₂O—N ha⁻¹ y⁻¹. The results indicate that the application of organic manure also had a significant effect on N₂O emissions, which combined with the use of chemical N fertilizer increased about 20% over the whole year. A weak correlation was found between N₂O emissions and soil available NH⁺₄ –N content. Average annual N₂O emission from fertilized soils was estimated to be 57.1 mg N₂O m⁻² h⁻¹, which is in good agreement with the average emission of 52.7 μg N₂O m⁻² h⁻¹ reported in other fertilized soil flux studies at different locations in China.