Microscale alterations in soil physical characteristics resulting from long-term soil health practices can contribute to changes in soil nitrous oxide (NO) emissions. In this study, we investigated soil NO emissions in relation to pore characteristics influencing soil gas diffusivity under long-term tillage and cover cropping practices. Intact soil cores from tillage (conventional tillage, Conv. T versus no tillage, NT) and cover crop (hairy vetch, HV versus no cover crop, NC) treatments were used for NO measurements and computed tomography (CT) scanning. Using X-ray CT technique with a resolution of 59 μm, pore structure parameters including macroporosity, number of macropores, anisotropy, fractal dimension, tortuosity, and connectivity were determined. The results showed that Conv. T and HV emitted significantly higher NO than NT and NC, respectively. A similar trend was observed for macroporosity, Conv. T soils had 27.4 % higher CT-derived macroporosity than the NT soils and HV increased macroporosity by 31.1 % over the NC treatment. The number of macropores and fractal dimension were significantly higher whereas degree of anisotropy was significantly lower under HV compared to NC. In the upper 3 cm of soil, HV had a connected porosity, whereas the pores were disconnected and isolated in NC. These CT-derived properties; however, were not impacted by tillage treatments. NO emissions were positively and significantly correlated to relative soil gas diffusivity, CT-derived macroporosity, number of macropores, and fractal dimension. Our results demonstrated that soil macroporosity and relative gas diffusivity could lead to improved understanding and predictability of NO emissions under high soil moisture conditions.

中文翻译：

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计算机断层扫描揭示了长期耕作和覆盖种植实践下大孔控制的 N2O 排放

长期土壤健康实践造成的土壤物理特性的微小变化可能会导致土壤一氧化二氮（NO）排放量的变化。在本研究中，我们研究了长期耕作和覆盖种植实践中影响土壤气体扩散率的孔隙特征与土壤 NO 排放的关系。使用耕作（传统耕作，Conv. T 与免耕，NT）和覆盖作物（毛野豌豆，HV 与无覆盖作物，NC）处理的完整土芯进行 NO 测量和计算机断层扫描 (CT) 扫描。采用分辨率为59 μm的X射线CT技术，测定了孔隙结构参数，包括大孔隙率、大孔隙数量、各向异性、分形维数、弯曲度和连通性。结果表明，Conv。 T 和 HV 排放的 NO 分别显着高于 NT 和 NC。大孔隙率、Conv 也观察到类似的趋势。 T 土壤的 CT 衍生大孔隙率比 NT 土壤高 27.4%，HV 比 NC 处理增加大孔隙率 31.1%。与 NC 相比，HV 下的大孔数量和分形维数显着较高，而各向异性程度显着较低。在土壤上部 3 cm 中，HV 具有连通的孔隙度，而 NC 中的孔隙是不连通且孤立的。这些 CT 衍生的特性；然而，并未受到耕作处理的影响。 NO 排放量与相对土壤气体扩散率、CT 得出的大孔隙度、大孔隙数量和分形维数呈显着正相关。我们的结果表明，土壤大孔隙度和相对气体扩散率可以提高对高土壤湿度条件下 NO 排放的理解和预测。