Classification of Bound Residues Soil Organic Matter: Polymeric Nature of Residues in Humic Substance

In the course of studying the decomposition of radioactive, foreign organic compounds in soil, we invariably find radioactivity associated with the soil organic matter. This associated radioactivity has generally not been identified because of the difficulty of working with the material. As the incubation time for the organic compound in soil increases, the amount of radioactivity in the soil organic matter also generally increases. Consequently, it has become increasingly important to have some notion of how this radioactivity is combined structurally with the soil organic matter. The organic matter of soils consists of a mixture of plant and animal products in various stages of decomposition, of substances synthesized biologically and/or chemically from the breakdown products, and of microorganisms and small animals and their decomposing remains. To simplify this very complex system, organic matter is usually divided into two groups: (a) nonhumic substances and (b) humic substances. Nonhumic substances include compounds