Soil Organic Matter: II. Studies of the Origin and Chemical Structure of Soil Humic Acids
1961
Johnston, Harry H.
Small quantities of soil humic acids were supplied to cultures of Nostoc muscorum, resulting in stimulation of growth and nitrogen fixation. Various organic compounds were added to compare stimulations and structural relationships. Of all the compounds tested, catechol and humic acids were found to give the greatest increases of nitrogen fixed. Part of the increase in nitrogen fixation was thought to be due to boron contained by the humic acids. Lignin oxidized by H₂O₂ and microorganisms was analyzed by infrared spectroscopy. The product formed by microorganisms gave a material with similar paper electrophoretic mobility as natural humic acids. Controlled degradation of humic acids and lignin gave various phenols. Humic acid chromatograms showed four phenols present: catechol, phenol, guaiacol, and o-cresol. One spot found in the humic acid chromatograms has not yet been identified. Bean root lignin when subjected to the same degradation gave a spot in the same position and with the same color. Guaiacol and phenol were also identified from bean root lignin.
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