Soil organic carbon (SOC) and soil inorganic carbon (SIC) are of longstanding interest due to their relationship with other key soil properties and indications for soil health and carbon storage. At the USDA-NRCS Kellogg Soil Survey Laboratory (KSSL), total carbon (SOC + SIC) is determined via dry combustion analysis, while calcium carbonate (CaCO3) equivalent is determined via manocalcimetry. For calcareous (carbonate bearing) samples, SIC is estimated as 12 % of CaCO3 equivalent, while SOC is estimated as the difference between measured total carbon and estimated SIC. An alternative dry combustion method for the measurement of SOC and SIC pools was evaluated with the goal of directly measuring – not estimating – inorganic and organic carbon on calcareous samples. The alternative temperature ramp dry combustion (TRDC) method comprises two variants that differ in ramp cycle and carrier gases used. One variant operates under continuous oxygen and has temperature ramp plateaus of 400, 600 and 900 °C; thus, it is referred to as the non-gas switching variant or TRDCNGS. The other variant operates under oxygen until 400 °C, then switches to nitrogen gas for a ramp to 900 °C, then reintroduces oxygen at 900 °C; thus, it is referred to as the gas switching variant or TRDCGS. Both variants were applied in duplicate to 110 diverse samples, including 32 calcareous samples, from across the USA that had been previously characterized by the KSSL. Samples were selected to capture wide variability in carbon contents. Comparing carbon data outcomes with data from the legacy KSSL methods revealed the TRDCGS variant as best for calcareous samples, whereas the TRDCNGS variant was preferred for non-calcareous samples. A combination of the two method variants offers an accurate and direct measurement of SOC and SIC. For calcareous samples, mid-infrared (MIR) spectral analysis demonstrated TRDC method as slightly more accurate than legacy KSSL methods for estimating SOC and SIC.

中文翻译：

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使用燃烧分析同时测量土壤有机碳和无机碳


土壤有机碳 （SOC） 和土壤无机碳 （SIC） 因其与其他关键土壤特性以及土壤健康和碳储存的指示的关系而受到长期关注。在美国农业部-NRCS 凯洛格土壤调查实验室 （KSSL），总碳 （SOC + SIC） 是通过干燃烧分析确定的，而碳酸钙 （CaCO3） 当量是通过测压法确定的。对于钙质（含碳酸盐）样品，SIC 估计为 CaCO3 当量的 12%，而 SOC 估计为测得的总碳与估计的 SIC 之间的差值。评估了一种用于测量 SOC 和 SIC 池的替代干燃烧方法，目的是直接测量（而不是估计）钙质样品上的无机碳和有机碳。替代温度斜坡干燃烧 （TRDC） 方法包括两种变体，它们在斜坡循环和使用的载气方面有所不同。一种变体在连续氧气下运行，温度斜坡平台为 400、600 和 900 °C;因此，它被称为非气体切换变体或 TRDCNGS。另一种变体在氧气下运行至 400 °C，然后改用氮气升至 900 °C，然后在 900 °C 时重新引入氧气;因此，它被称为气体切换变体或 TRDCGS。两种变体一式两份应用于来自美国各地的 110 个不同样品，包括 32 个钙质样品，这些样品之前已由 KSSL 表征。选择样品以捕获碳含量的广泛变化。将碳数据结果与传统 KSSL 方法的数据进行比较，发现 TRDCGS 变体最适合钙质样品，而 TRDCNGS 变体更适合非钙质样品。 两种方法的组合提供了 SOC 和 SIC 的准确和直接测量。对于钙质样品，中红外 （MIR） 光谱分析表明，TRDC 方法在估计 SOC 和 SIC 方面比传统的 KSSL 方法略准确。