The Characteristics Of Nitrous Oxide Fluxs From The Soils And Plants Of Typical Crop Fields In North China Plain

Nitrous oxide (N₂O) is a long-lived trace gas. The continuous increase of atmospheric N₂O concentration not only caused global warming but also destroyed ozone layer(IPCC 1997).Recent research suggested that about 80% net increase of atmospheric N₂O was probably caused by agro-ecosystems. China is a large agricultural country with a population of 1.3 billion.To meet the food requirements of the increasing population, the use of synthetic nitrogen fertilizer increases annually. About 1.74 ×10⁷ and 2.22 ×10⁷ tons of synthetic N were consumed in 1990 and 1995, respectively(China Agricultural Yearbook, 19980-1996),these amounts of N accounted for one fourth of the world total consumption. Therefore, the estimation of direct N₂O emission from agricultural fields in China is of great significance in the estimation of global N₂O emission.Experimental studies were done at the Yucheng comprehensive experimental station of the Chinese Academy of Sciences during 2003-2004.Soil and crop N₂O fluxes were measured by using close chamber method in typical cotton, summer maize, soybean and winter wheat fields in North China Plain. Both seasonal and daily change rules of N₂O fluxes from soil and plant were carefully monitored. Furthermore, variation charateristcs of N₂O fluxes under different climate condition were studied. Environmental factors which are responsible for N₂O fluxes were also proposed.The results show that the soils of cotton, maize, soybean and wheat fields are all the sources of atmospheric N₂O. The average N₂O fluxes of soil in cotton, maize , soybean and wheat fields were 88.2, 244.3, 177.8 and 51.2μ g.m^-2.h^-1 respectively .The crops of cotton, maize, soybean and wheat are the sink of atmospheric N₂O. The average N₂O fluxes of crops in cotton, maize , soybean and wheat were 401.1 μ -562.1 and -50.6 μg.m^-2.h^-1' respectively . There were significant seasonal variations of N₂O fluxes in cotton , maize soybean and wheat fields . The diurnal variation of N₂O emission from the soil of cotton and wheat fields presented a single-peak curve or a double-peak curve. The N₂O fluxes reached peak value at about 11:00-l 5:00 and 1:00-4:00. The diurnal variation of N₂O emission from the soil of maize field presented a double-peak curve. The N₂O fluxes reached...