Effect of Nitrogen Application Rates on Nitrous Oxide Emission during Crop Cultivations in Upland Soil

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BACKGROUND: Generally, nitrogen (N) fertilization higher than the recommended dose is applied during vegetable cultivation to increase productivity. But higher N fertilization also increases the concentrations of nitrate ions and nitrous oxide in soil. In this experiment, the impact of N fertilization was studied on nitrous oxide (<TEX>$N_2O$</TEX>) emission to standardize the optimum fertilization level for minimizing <TEX>$N_2O$</TEX> emission as well as increasing crop productivity. Herein, we developed <TEX>$N_2O$</TEX> emission inventory for upland soil region during red pepper and Chinese milk vetch cultivation. METHODS AND RESULTS: Nitrogen fertilizers were applied at different rates to study their effect on <TEX>$N_2O$</TEX> emission during red pepper and Chinese milk vetch cultivation. The gas samples were collected by static closed chamber method and <TEX>$N_2O$</TEX> concentration was measured by gas chromatography. The total <TEX>$N_2O$</TEX> flux was steadily increased due to increasing N fertilization level, though the overall pattern of <TEX>$N_2O$</TEX> emission dynamics was same. Application of N fertilization higher than the recommended dose increased the values of both seasonal <TEX>$N_2O$</TEX> flux (94.5% for Chinese cabbage and 30.7% for red pepper) and <TEX>$N_2O$</TEX> emission per unit crop yield (77.9% for Chinese cabbage and 23.2% for red pepper). Nitrous oxide inventory revealed that the <TEX>$N_2O$</TEX> emission due to unit amount of N application from short-duration vegetable field in fall (autumn) season (6.36 kg/ha) was almost 70% higher than that during summer season. CONCLUSION: Application of excess N-fertilizers increased seasonal <TEX>$N_2O$</TEX> flux especially the <TEX>$N_2O$</TEX> flux per unit yield during both Chinese cabbage and red pepper cultivation. This suggested that the higher N fertilization than the recommended dose actually facilitates <TEX>$N_2O$</TEX> emission than boosting plant productivity. The <TEX>$N_2O$</TEX> inventory for upland farming in temperate region like Korea revealed that <TEX>$N_2O$</TEX> flux due to unit amount of N-fertilizer application for Chinese cabbage in fall (autumn) season was comparatively higher than that of summer vegetables like red pepper. Therefore, the judicious N fertilization following recommended dose is required to suppress <TEX>$N_2O$</TEX> emission with high vegetable productivity in upland soils.