ORGANIC-MATTER EXTRACTION FROM SOILS WITH WATER AT HIGH-PRESSURE AND TEMPERATURES

The objective of this research was to develop a procedure for the more specific extraction of major organic matter (OM) components from soils. The method was tested on Ap horizons of a Haplaquoll, a Cryoboroll, and a Haploboroll, and on the Bh horizon of a Haplaquod. The four soils were extracted for 2 h with distilled water at a constant pressure of 17.2 MPa and at temperatures of 150, 200, and 250-degrees-C. The OM extracts obtained were characterized by chemical methods, infrared (IR) and nuclear magnetic resonance (NMR) spectroscopy, and pyrolysis-field ionization mass spectrometry (Py-FIMS). With one exception, relatively more of the soil N (18-53%) than soil C (17-40%) was extracted from the four soils at the three temperatures. Recoveries of N at 200 and 250-degrees-C were superior to those reported for extractions by 0.1 M Na4P2O7 solution from the same soils, while C recoveries were higher from the Bainsville and Regina soils. In general, extracts obtained at 200-degrees-C were richest in carbohydrates and especially in N components. The C-13-NMR spectra showed that most of the C in the extracts was aliphatic, occurring in the form of noncarbohydrate carbons bonded to OH and O. The Py-FI mass spectra indicated that the extracts contained polysaccharides, n-fatty acids, n-alkanes, n-alcohols, sterols, N compounds (pyrroles and pyridines), and mono- and dilignins, all typical OM components. Extracts obtained at 150-degrees-C were enriched in n-alcohols and diols, whereas extracts at 250-degrees-C were rich in fatty acids. For the extraction of carbohydrates and N components, we recommend an extraction temperature of 200-degrees-C; for soils rich in clay minerals, extractions at 250-degrees-C may be more efficient. For studies on paraffinic OM components, extraction at 150-degrees-C may be appropriate.