Chemical properties of humic and fulvic acid products and their ores of origin

Abstract

Commercial products consisting of humic and fulvic acids are thought to boost plant growth and economic yield in cropland agriculture. The specific mechanism for their benefit is unknown, in part because little information is available on the chemical nature of these products. We examined the chemical nature of eight humic acid products, three fulvic acids and seven of their source materials, lignite and leonardite ores, and humic shales. All samples were from the United States and Canada. Analysis by 13C cross polarization/magic angle spinning nuclear magnetic resonance spectroscopy found that the humic acid products and the ores were dominated by large signals at aliphatic C (ca. 30 ppm) and aromatic C (ca. 130 ppm). These products were distinguished from one another by their relative proportions of aromatics and aliphatics and relative percentages of smaller signals for carboxyl C (approximately 175 ppm) and ketones/aldehydes C (ca. 200 ppm). These samples were also extracted for their concentrations of seven carbohydrates through anion exchange chromatography and pulsed amperometric detection. All ores and humic acid products had low concentrations of carbohydrates. The ores and products made without alkali extraction had slightly greater concentrations of carbohydrates than did extracted products, suggesting that alkali extraction for production of the humic acid products discriminated against carbohydrates. Results will also be discussed for sample concentrations of amino acids, two amino sugars, and lignin-derived phenols. Although these products share the same dominant chemical traits, they cannot be considered as chemically similar until the chemical mechanism for their effect on plant growth is identified and the corresponding compound(s) or functional group(s) is/are measured in these products and ores. Until then, field efficacy established for one product cannot be transferred to other products.