Comparing publicly available databases to evaluate soil organic carbon in Maine, USA

Abstract

AbstractElevated 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.