Grazed pastures and cultivated fields are significant sources of greenhouse gas (GHG) emissions, in particular N₂O emissions derived from fertilizer deposition and animal excreta. Net surface emissions rely on subsurface gas transfer controlled mainly by diffusion, expressed as the soil‐gas diffusivity (D_p/D_o). The value of D_p/D_o is a function of soil air‐filled porosity (ε) and gaseous phase tortuosity (Ʈ), both of which vary with soil physical properties including soil texture and structure. Agricultural soils are often structurally aggregated and characterized by two distinct regions (inter‐ and intra‐aggregated pores), however, such soils are subjected to frequent compaction and tillage resulting in alteration to structural arrangement. In this study, a comparative analysis between the Currie (1960) and Taylor (1949) methods was performed to provide a computational insight into selecting an appropriate method for calculating D_p/D_o in agricultural soils. Currie's (1960) method was chosen for further analysis of the soils in this study. Results show that the D_p/D_o in aggregated soil cannot be expressed using a simple linear, power law or combined linear and power law functions due to the presence of two‐region characteristics. A new “Two‐Region model” was developed to parameterize the D_p/D_o of aggregated soils, and tested against repacked samples from two Sri Lankan agricultural soils. This Two‐Region model clearly distinguished tortuosity effects on gas movement with respect to density and textural variations within and between aggregates and outperformed previous models. The fitting parameters (α₁, α₂, β₁ and β₂) varied correspondingly with soil density, and the weighting factor (w) clearly distinguished the boundary between the two regions (inter‐ and intra‐aggregates) of structured soils. The model developed will be of interest to those seeking to model the diffusion of GHG emissions and gas exchange between the atmosphere and soils.

中文翻译：

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基于气体扩散系数的聚集农业土壤特征

放牧的牧场和耕地是温室气体（GHG）排放的重要来源，尤其是化肥沉积和动物排泄物产生的N ₂ O排放。净表面排放依赖于主要由扩散控制的地下气体转移，表示为土壤-气体扩散率（D _p / D _o）。D _p / D _o的值是土壤充气孔隙率（ε）和气相曲折度（Ʈ）的函数，二者随土壤物理特性（包括土壤质地和结构）的不同而变化。农业土壤通常在结构上聚集，并具有两个不同的区域（内部和内部聚集的孔隙）特征，但是，此类土壤经常进行压实和耕作，导致结构布置发生变化。在这项研究中，对Currie（1960）和Taylor（1949）方法进行了比较分析，从而为选择合适的计算农业土壤中D _p / D _o的方法提供了计算见解。本研究选择了Currie（1960）方法对土壤进行进一步分析。结果表明D由于存在两个区域特性，因此无法使用简单的线性，幂定律或线性和幂定律组合函数来表示聚集土壤中的_p / D _o。开发了一种新的“两区域模型”以对聚集土壤的D _p / D _o进行参数化，并针对来自两种斯里兰卡农业土壤的重新包装样品进行了测试。这个两区域模型清楚地区分了曲折度对气体运动的影响，这涉及骨料内部和之间的密度和纹理变化，并且优于以前的模型。拟合参数（α ₁，α ₂，β ₁和β ₂）随土壤密度的变化而变化，加权因子（w）清楚地区分了结构化土壤的两个区域（集聚体内部和集聚体之间）的边界。那些希望为温室气体排放的扩散和大气与土壤之间的气体交换建模的模型将对所开发的模型感兴趣。