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 fi om 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 mug 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 mug 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 NH4+ N content. Average annual N2O emission from fertilized soils was estimated to be 57.1 mug N2O m(-2) h(-1), which is in good agreement with the average emission of 52.7 mug N2O m(-2) h(-1) reported in other fertilized soil Bur studies at different locations in China.