Quantifying Direct N2O Emissions from Paddy Fields During Rice Growing Season in Mainland China in 1980s and 1990s

Nitrous oxide (N

2

O) is one of key greenhouse gases that cause global warming. It continues to rise at a rate of approximate 0.26% per year and has reached a concentration of 319 ppb (10

-9

mol mol

-1

) in 2005 (IPCC 2007a). Agriculture accounts for about 60% of global anthropogenic N

2

O emissions. Globally, agricultural N

2

O emissions have increased by nearly 17% from 1990 to 2005 (IPCC 2007b), and are projected to increase by 35–60% up to 2030 due to increased nitrogen fertilizer use and increased animal manure production (FAO 2003). The emissions of N

2

O that result from anthropogenic N inputs, occur through a direct pathway (i.e. directly from soils to which the N is added), and through two indirect pathways: volatilization of compounds, such as NH

3

and NO

X

and subsequent redeposition, and through leaching and runoff. Relative to the indirect pathways, the direct emission contributes most to the agricultural N

2

O sources (Zheng et al. 2004). Thus, a good estimate of direct N

2

O emission from agricultural fields will help assess its global source strength.