Dissolved Organic Matter Extracted With Water and a Saline Solution From Different Soil Profiles

The organic matter fraction present in soil solution and passing a filter of pore size of 0.45 mu m is operationally defined as dissolved organic matter (DOM). In this work, DOM was extracted with either water or a saline solution from the various horizons of four different soil profiles, either cultivated or not, and characterized by chemical analysis and spectroscopic techniques such as emission fluorescence spectroscopy and Fourier transform infrared spectroscopy. Water and a saline solution extracted different amounts of DOM. These results imply that the effect of colloidal dispersion exerted by water resulted in a higher release and solubilization of organic matter compared with colloidal flocculation exerted by the saline solution. Thus, the extractant used for DOM extraction from soil must be taken into due account for its effect on the nature of DOM extracted. Our results corroborate the need to standardize extraction methods. Fluorescence emission spectra provided evidence of a variation in DOM composition as a function of depth along the soil profile, which was possibly related to adsorption of aromatic molecules on soil colloids. Finally, land use also seemed to influence the chemical nature of DOM along the soil profile.