An Introduction to Organic Matter in Mineral Soils

Abstract

In mineral soils, most humus is associated with inorganic materials, particularly clays, and the interactions have profound effects on both the organic and inorganic materials. The mechanisms of interactions of organic materials with clay minerals and with oxides are reasonably well understood from laboratory studies. The association of organic molecules with minerals is normally examined initially by means of adsorption isotherms in which the amount of the organic compound sorbed is plotted against the equilibrium concentration remaining in solution. The two major physical properties that can be used to separate the range of organo-mineral complexes are size and density. The organic-matter content of soils depends on the accessibility of organic materials to a hungry microbial population. Microbial tissue exhibits considerable variation in composition and persistence in soil, with cell-wall components generally being more resistant than cytoplasm.