Soil nitric and nitrous oxide emissions from agricultural and tidal flat fields in southwestern Korea

A closed chamber system was used to measure fluxes of NO and N₂O from soil surfaces. The research sites were located in southwestern Korea, and measurements were conducted during summer 2000 to assess the NO source strength of agricultural soils (upland and rice paddy) and tidal flats. Research for tidal flat soil fluxes was initially attempted to investigate their significance on the nitrogen budget in Korea. Soil samples were taken on each experimental day and analyzed for soil pH, soil moisture, and total Kjeldahl nitrogen (TKN = organic nitrogen + NH₄-N + NO₃-N). Soil nitrogen and NO flux increased significantly after applying nitrogen fertilizer to agricultural fields. Average NO and N₂O fluxes were 84.8 ng N m^–2 s^–1 (range: 0.1~464.2 ng N m^–2 s^–1) and 67.8 ng N m^–2 s^–1 (range: 4.0~199.7 ng N m^–2 s^–1), respectively, from upland soils planted with green onions. Average N₂O flux from soils planted with soybean was 52.5 ng N m^–2 s^–1 (range: 4.0~463.2 ng N m^–2 s^–1). Based on statistical test, no significant difference in N₂O fluxes between green onion and soybean field was observed (t-statistic value = 1.2299; t_98,0.05 = 1.6606). Soil NO and N₂O fluxes from rice paddies and tidal flats were significantly lower than those from uplands; anoxic condition due to water saturation could limit the gas productions by processing nitrate reduction. Key words: NO and N₂O flux, biogenic emission, closed chamber technology, agricultural soils, tidal flat nitrogen emission.