This collection contains air-dried soil samples collected at NEON terrestrial sites (NEON sample class: sls_bgcSubsampling_in.bgcArchiveID). Soil biogeochemical samples are collected once every 5 years. Soil sampling is conducted to a maximum depth of 30 ± 1 cm where possible. Mineral horizons are sampled using a 2 ± 0.5 inch diameter coring device, when possible. Where rockiness or other site soil characteristics make it difficult to use this diameter range, other diameters will be employed. When organic and mineral horizons are present within a single profile they are separated prior to analysis and archiving. However, other sub-horizons will not be separated. Soil from the O horizon is homogenized and air-dried, but NOT sieved prior to archiving. Soil from the mineral horizons is homogenized and air-dried and then sieved (2 mm) prior to archiving. If multiple cores are collected at a location, the cores are combined to create one composite sample of the M horizon. The number of M horizon cores needed per location depends on factors including the soil corer used, type of sampling bout, and local soil conditions. Soil subsamples are archived in glass jars and stored at room temperature. See related links below for protocols and NEON related data products. A more detailed characterization of the dominant soil types occurred during the construction period of NEON through two projects. One project was led by the Terrestrial Instrumentation System (TIS) unit and included a thorough description of one large soil pit ("megapit") dug at the NEON tower location from the surface to 2 meters depth (or bedrock) at each core and relocatable site. These data are available in NEON data products Soil Physical Properties (Megapit) and Soil Chemical Properties (Megapit). The second project was carried out by the U.S. Department of Agriculture (USDA) and the Natural Resources Conservation Service (NRCS) and characterized soil physical and chemical properties (including bulk density) to 1 m depth at a subset of the Terrestrial Observation System (TOS) distributed soil plots, many of which overlap with ongoing NEON soil sampling. These data are available in NEON data products Soil Chemical Properties (Distributed Initial Characterization) and Soil Physical Properties (Distributed Initial Characterization).