Soil Organic Matter eKonomics News Team Share This: The organic fraction of the soil exclusive of undecayed plant and animal residues. See also humus.Related Articles: Managing Sulfur for Spring Wheat in the Red River ValleySulfur: The Other Essential Soil NutrientDo Soil Microbes Add Nutrients to My Soil?Top 3 Causes of Yellow WheatCover Crops and Nitrogen Management