Submitted to: Soil Science
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 9/23/1999
Publication Date: N/A
Interpretive Summary: Organic materials in soils are made up of a combination of components in close association. The organic fraction provides a network for water, air, and nutrient interaction. Among individual components of the organic matter are the humic substances -humic acid, fulvic acid, and humin. These are especially important because they are the most active agents for binding soil particles (aggregation) and for transporting chemical pollutants (pesticides). Analyses of the humic materials isolated from smaller soil particles (clay and silt) for contents of elements, amino acids, and sugars showed larger quantities of these substances present where corn stover residue was not returned to the soil. This implies that more microbial activity took place with addition of residues, as well as more protection of silt- compared with clay-sized particles. Other results using "finger-print" methods (NMR and FTIR) and naturally-occurring isotopes of carbon and nitrogen showed differences in the humic substances as to plant or microbial origin in the clay or silt fractions. By isolating, fractionating, and characterizing these components, we are able to uncover the processes by which they carry out their activities. Understanding their modes of action will allow us to find ways of preventing undesirable chemicals from polluting the soil and groundwater. Impact from this research will be felt by environmentalists, farmers, scientists, and the general public, all who have a stake in preserving both environmental quality of agricultural ecosystems, and in maintaining profitable farming operations.
Technical Abstract: In a small plot field study on a Waukegan silt loam soil, annual applications of 20 g N m**-2 were made prior to planting corn (Zea mays L.) each May for 8 years. Subplots were fertilized with 0.8 g **15N m**-2. Soil treatment in the fall either incorporated the chopped corn stover using a rototiller, or the stover was removed from the plots. Soil samples taken in the fall were ultrasonicated, separated into clay- and silt-sized fractions, and exhaustively extracted with 0.1 M sodium pyrophosphate (Na4P2O7) plus 0.1 M NaOH (pH 12.6). Humic (HA) and fulvic (FA) acids were isolated using the International Humic Substances Society (IHSS) procedures. A variety of analytical methods were employed. The most useful information was obtained from amino acid (AA) and neutral sugar (NS) analyses, and from cross polarization magic angle spinning (CPMAS) **13C- NMR and **13C data. Overall, the corn stover amendments did not have large effects on the compositions of the humic substances (HS) from the differen sized separates, but there were differences in the relative abundances of some AA and NS in the HAs and FAs of the different sized separates. The NMR and **13C data provided evidence of some compositional differences and extents of humification between the HS from the clay- and silt-sized separates. It is concluded that the silt-sized particles were microaggregates of clay-sized particles, and the HS in these microaggregates were partially protected from bioalteration. These HS had greater resemblances to the plants of origin than did those associated with the clays. The compositions of the HAs and FAs were similar to those of the (Mollisol) soil standard of the IHSS, but were different from humic samples from other (non-Mollisol) soil types.