Increasing organic matter content of soils is important from the perspective of increasing both soil quality and sequestration of atmospheric CO₂.  Past sorption studies with humic substances have been reported, but those with naturally occurring, agriculturally-derived dissolved organic matter (DOM) ligands are limited.  We investigated the sorption of DOM extracted from: above-ground biomass of wheat straw (Triticum aestivum L.), corn residue (Zea mays L.), soybean residue (Glycine max (L.) Merr.), and hairy vetch residue (Vivia billosa L.); below-ground biomass from corn, soybean, canola (Brassica napus L.), and green bean (Phaseolus vulgaris L.); and beef, dairy, poultry, and swine animal manures onto goethite.  The apparent weight-averaged molecular weight (MW) of the DOM was measured by high performance-size exclusion chromatography and ranged from 312 to 1074 g mol^-1.  Sorption was directly related to the initial MW of the DOM extract and MW analysis of the solution prior to and after sorption indicated that the ligands >1800 g mol^-1 were preferentially sorbed resulting in fractionation of the DOM upon reaction with a mineral surface.  PARAFAC analysis of the DOM fluorescence spectra revealed four components (fluorophores).  Comparison of the fluorophore concentrations before and after sorption indicated that only fluorophore #2 with an EX maximum at 320 nm and EM maximum at 450 nm was sorbed.  This fluorophore has been characterized as “fulvic-like” by other researchers.   The multiple regression equation obtained for goethite was Sorption (µg C m^-2) = 11.38 + 46.9(fluorophore #2) +0.021(MW), r² = 0.72.  This result indicate that MW and concentration of the fulvic-like fluorophore are important factors in controlling the sorption of DOM to the goethite surface.