[Effect of Film Mulching, Straw Retention, and Nitrogen Fertilization on the NO and N Emission in a Winter Wheat Field].

In order to explore the characteristics of NO emissions from winter wheat fields in the Loess Plateau under different farming methods and nitrogen levels, the dynamic changes in NO emissions from rain-fed winter wheat fields were quantified using static box-gas chromatography. Winter wheat 'Xiaoyan22' was used as the material, and a two-factor split area design was adopted. The conventional tillage (CT), straw incorporated into soil (SM), and flat film mulching (FM) were assigned as the main plot, and three nitrogen fertilizer rates (no nitrogen fertilization, 20% nitrogen reduction (144 kg·hm), and conventional nitrogen application (180 kg·hm)) were assigned as a split plot. Taking CT as a control, the effects of FM and SM on soil NO emissions under different nitrogen rates were assessed. Furthermore, the correlation between relevant environmental factors and NO emission flux were analyzed, and N emissions were estimated using empirical formulas. The results showed the following:the NO emissions from the soil of each nitrogen treatment occurred within 20 days, and NO emission flux peaked within two weeks post-fertilization. The average NO flux, the total NO emissions, and the global warming potential of NO were 1.92-22.75 μg·(m·h), 0.10-0.46 kg·hm, and 26.72-122.15 kg·hm, respectively. The NO emission coefficient of fertilizer nitrogen was 0.05%-0.28%. The total N emissions ranged from 0.70-1.82 kg·hm. The N fertilization and film mulching significantly increased the NO emission flux (<0.05) and the cumulative NO emissions (<0.05); however, SM marginally reduced the total NO emissions. The NO emission coefficient and global warming potential of fertilizer nitrogen under FM were significantly higher than those under CT and SM (<0.05). The NO emissions without nitrogen treatment were only significantly positively correlated with soil water-filled pore spaces (WFPS) (<0.05); the NO emissions in the N fertilization condition were significantly positively correlated with WFPS, (NO-N), (NH-N), and 0-5 cm soil layer temperature (<0.05). Overall, under the condition of no fertilization, water was the main factor to control the nitrogen transformation and soil NO emission; nevertheless, under the N fertilization condition, both nitrification and denitrification contributed to the NO emissions in the rain-fed winter wheat fields. Film mulching practice and nitrogen application markedly increased the NO emissions, fertilizer nitrogen emission coefficient, and global warming potential in the rain-fed winter wheat fields. Nonetheless, straw incorporated into the soil resulted in a marginal reduction in NO emissions.