Nitrous oxide (N2O) is a greenhouse gas emitted from the natural ecosystem (10 Tg year-1 globally) and anthropogenic sources (5.7 Tg year-1). Agriculture, which comprises about 68% of total anthropogenic N2O emissions (Schlesinger, 1997), is the most important source of global N2O emissions. The Greenhouse Gas Inventory Office (GIO) estimated that total Japanese N2O emissions were 87 Gg in 2005, 46% of which originated from agriculture (GIO, 2007), illustrating the importance of agriculture in N2O emissions. GIO (2007) summarized and indicated agricultural N2O emissions into three sources: manure handling, agricultural land, and crop residue burning. However, in terms of agro-environmental science, this division is too crude to enable the responsibility of each agricultural sector to be analyzed.
In this study, we estimated N2O emissions from nine agricultural sectors in Japan (see Framework section) in 1985, 1990, 1995, 2000, and 2005. We then evaluated the direct and indirect emissions from crop production and livestock husbandry and the problems of each agricultural sector. We also discussed the uncertainties around methods of estimation and the mitigation of N2O emissions for future sustainable agriculture.
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