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Organic Matter Extraction from Soils with Water at High Pressure and Temperatures

Land Resource Research Centre, Agriculture Canada, Central Experiment Farm, Ottawa, ON K1A 0C6, Canada

H.-R. Schulten

Fachhochschule Fresenius, Dep. of Trace Analysis, Dambachtal 20, 6200 Wiesbaden West Germany

D. A. Angers

Research Station, Agriculture Canada, Sainte-Foy, PQ G1V 2J3, Canada

* Corresponding author.

ABSTRACT

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 °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 °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 °C were richest in carbohydrates and especially in N components. The ¹³C-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 °C were enriched in n-alcohols and diols, whereas extracts at 250 °C were rich in fatty acids. For the extraction of carbohydrates and N components, we recommend an extraction temperature of 200 °C; for soils rich in clay minerals, extractions at 250 °C may be more efficient. For studies on paraffinic OM components, extraction at 150 °C may be appropriate.

Contribution no. 90-18 (LRRC) and 380 Ste-Foy Res. Stn.

Received for publication March 7, 1990.