Soil Organic Matter in Nano-Composite and Clay Fractions, and Soluble Pools of the Rhizosphere

Soil organic matter (SOM) has been studied in physical fractions (i.e., aggregates), chemical components (i.e., humic substances); and biological constituents (i.e., microbial biomass), or represented in kinetic compartments in simulation models (i.e., Century). In soils most organic matter is found as organo-mineral complexes, the interactions between inorganic and organic matter have been studied by Schnitzer and Kodama (1992). The physical domains of organic matter involve hierarchical units of aggregates and particle size fractions (Oades and Waters, 1991). The chemical domains involve chemically extracted humic substances (Schnitzer and Kodama, 1975), or several chemical classes of compounds in whole soil as characterized in mass spectrometry studies (Schnitzer and Schulten, 1992). The biological components and their interactions with inorganic matrices and organics control the flows of energy, carbon, nitrogen and other crop nutrients (Monreal and McGill, 1997). Another important component of organic matter is the soil solution, where chemical, biochemical and physico-chemical reactions occur (Monreal and McGill, 1997). The latter reactions affect supply of crop nutrients, the type of microbial communities, and molecular structures of soil organic matter (Monreal et al., 1997). In soil microsites organic matter binds to clay colloids and other minerals to form domains of nanocomposites at various arbitrary scales ( 1000 nm). On the other hand, bacteria may be considered as single domain microparticles or nanomolecular catalytic assemblies. Living communities of microorganisms in soils produce and utilize diverse nanoparticles during their metabolic reactions of oxidation and reduction of growth and energy synthesis (35). Thus, the