ODM2 Variable Name Controlled Vocabulary ODM2 Working Group A vocabulary for describing the name of Variables. Soil organic matter (SOM) density fractionation Density fraction of Soil organic matter (SOM) in soil. Soil organic matter (SOM) is the organic matter component of soil, consisting of plant and animal residues at various stages of decomposition, cells and tissues of soil organisms, and substances synthesized by soil organisms. Wikipedia https://en.wikipedia.org/wiki/Mass_fraction_(chemistry) Added to support Critical Zone Observatory (CZO) data use cases.