Submitted to: World Congress of Soil Science
Publication Type: Abstract Only
Publication Acceptance Date: 8/14/2002
Publication Date: 8/14/2002
Citation: Clapp, C.E., Hayes, M., Mao, J. 2002. Studies of humic fractions from a mollisol soil. World Congress of Soil Science. p. 196 Interpretive Summary:
Technical Abstract: The present study deals with the humic components from a Waukegan Mollisol soil from the University of Minnesota Research and Outreach Center in Rosemount, Minnesota. The soils were fertilized annually before planting maize (Zea mays L.) each May for 15 years. Stover was either removed or incorporated into the soil, using a rototiller. Soil samples were ultrasonicated, separated into clay- and silt-sized fractions, and these fractions were exhaustively extracted, first with 0.1M sodium pyrophosphate at pH7, then sequentially with pyrophosphate at pH 10.6 and 12.6, and finally with dimethylsulfoxide (DMSO) + 12M HCl (6%). Two procedures were used to isolate the humic fractions. In the first, the humic acids (HAs) were precipitated at pH 1, dialyzed, then freeze dried. The fulvic acids (FAs) were isolated from the supernatant solutions on XAD-8 resin. In the second procedure the aqueous extracts were diluted and run through XAD-8 resin. Elemental, neutral sugar (NS), amino acids (AA), CPMAS 13C and 2-D (Correlation Spectroscopy) NMR, potentiometric titration, and delta 13C data were obtained for each fraction. Overall, the corn stover amendments did not have large effects on the compositions of the humic fractions from the different sized separates, but there were differences in the relative abundances of some AAs and NS in the HAs and FAs. The NMR and delta 13C data provided evidence of some compositional differences and extents of humification between the HS from the clay-and silt-sized separates. The silt-sized components were shown to be microaggregates of clay-sized particles, and the humic components were preserved in these. These components (in the silt-sized fraction) had greater resemblances to the plants of origin than did those associated with the clays. MSO-HCl extracts did not exhibit the properties of humin. The data showed that isolation at the different pH values provides a worthwhile fractionation, though it was clear that all fractions retain characteristics typical of Mollisols.