Elevated greenhouse gas (GHG) emissions have resulted in growing societal interest in natural climate solutions that include enhancing soil organic carbon (SOC). This study evaluated SOC from three USDA soil databases for Maine, a state that is nearly 90% forested. These databases were: (1) Forest Inventory and Analysis (FIA), (2) NRCS Soil Survey Geographic (SSURGO), and (3) Rapid Carbon Assessment (RaCA). We compared estimates of SOC density and concentration among databases and analyzed relationships between key soil properties and SOC densities and concentrations. Estimates of SOC density to a 20 cm depth which allows comparison among all three databases were 77 ± 1.2 Mg ha⁻¹, 95 ± 0.3 Mg ha⁻¹, and 39 ± 2.2 Mg ha⁻¹ for SSURGO, RaCA, and FIA, respectively. Significant differences existed among databases in SOC density at shallow depth increments, and marked differences existed among databases in the soil depths measured. Analysis of the influence of soil texture and drainage class on SOC highlighted the importance of silt and clay in SOC retention. A hypothetical increase in forest and agricultural SOC was compared to reported Maine GHG emissions to illustrate potential policy implications in the use of soil databases. We conclude that all three databases are valuable but not interchangeable. The database should be carefully chosen to match the objectives of the user.

中文翻译：

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比较可公开获得的数据库以评估美国缅因州的土壤有机碳

温室气体（GHG）排放量的增加已引起社会对包括增强土壤有机碳（SOC）在内的自然气候解决方案的兴趣。这项研究评估了缅因州的三个USDA土壤数据库中的SOC，该州森林覆盖率接近90％。这些数据库是：（1）森林清单和分析（FIA），（2）NRCS土壤调查地理（SSURGO）和（3）快速碳评估（RaCA）。我们比较了数据库中SOC密度和浓度的估计值，并分析了关键土壤特性与SOC密度和浓度之间的关系。可以对所有三个数据库进行比较的20厘米深度的SOC密度估计值分别为77±1.2 Mg ha ^-1、95 ±0.3 Mg ha ^-1和39±2.2 Mg ha ^-1分别用于SSURGO，RaCA和FIA。浅层深度增加时，SOC密度之间存在显着差异，而土壤深度之间数据库之间存在显着差异。对土壤质地和排水类别对SOC的影响的分析突出了淤泥和粘土在SOC保留中的重要性。将森林和农业有机碳的假设增加与报告的缅因州温室气体排放进行比较，以说明使用土壤数据库的潜在政策含义。我们得出结论，所有这三个数据库都是有价值的，但不可互换。应该仔细选择数据库以匹配用户目标。