Effect of No Tillage and Conventional-Tillage Practices on the Nitrous Oxide Emissions on the Cultivation of Soybean in Upland Soil in Korea.

Reduction of greenhouse gas (GHG) emissions from upland crop field as well as paddy field is being required, but little information on GHG emissions according to cultivation practices in upland field is available. Furthermore, there is a strong need to determine the optimal combination of tillage and fertilization practices that reduce the amount of nitrous oxide (N₂O) emissions while maintaining crop productivity. This study was conducted to evaluate the nitrous oxide emission in the cultivation of soybean during the 3 years of no-tillage (NT) and conventional-tillage (CT) practices, under the different kinds of fertilizers(chemical fertilizer, organic manure, hairy vetch) in the sandy loam soils in Cheongju, Republic of Korea that is located in the temperate climate zone. N₂O emissions, water-filled pore space (WFPS), soil temperature, soil mineral N content, soil total nitrogen stocks and yields were quantified, respectively. The average N₂O emission during a crop period (June to September) varied from 79.9 to 296.4 μg m^-2 hr^-1 in all treatments. Significantly (P < 0.05) highest and lowest N₂O emissions were measured in July and September, respectively. N₂O fluxes were significantly (P < 0.05) correlated with the soil temperature and mineralized N, but not with soil moisture content during the growing season of soybean. In July 2014, the hairy vetch plot in CT emitted the largest N₂O emissions (296.4 μg m^-2 hr^-1 ± 85.8[SD]). Whereas, the unfertilized plot in NT emitted the smallest N₂O emissions (79.94 μg m^-2 hr^-1 ± 11.1[SD]) in September 2014. And the following years had a similar trend. The 2-years (2014-2015) application of NT practice significantly (P < 0.05) decreased N₂O emission by 28 - 40% compared with CT. The evaluations of the yield for soybean have confirmed that NT with hairy vetch treatment had the highest value in yield. In the future, continued long-term research on the influence of various environmental factors on the generation of N₂O and the economic value of no-till farming practice is required.