Chemical characteristics and microbial degradation of humate

Abstract

Humates are often used in agriculture as a source of organic matter. This study was conducted to characterize a commercial humate and to evaluate its chemical and decomposition characteristics. Characterization methods included fractionization of humic and fulvic acids of the humate, based on their alkali/acid insolubility; elemental analysis; acidic functional group analysis; and E₄/E₆ ratio determinations. The humate consisted of the following: 58% organic matter, 32% ash, and 10% moisture. Humic fraction was mostly humic acid (76%), with some fulvic acid (18%). Organic elemental composition 59% carbon (C), 5% hydrogen (H), and 36% oxygen (O)] also suggests a humic‐acid nature. Inorganic elemental content of this humate, which was primarily aluminum (Al) 4.9%] and iron (Fe) 0.46%], reflects its spodic origin. Much of the Al present, however, results from the flocculant (alum) used at the mining site to precipitate the humate. The relatively low total acidity of this humate (250 cmol/kg) suggests the blockage of some of its functional groups by Al, Fe, and associated clay minerals. After purification, total acidity increased to 510 cmol/kg and acidity associated with carboxyl groups increased to 280 cmol/kg. Results of E₄/E₆ determinations for the humate (2.5) and the humic‐acid fraction (4.8) also suggested that the organic fraction was predominately humic acid. Decomposition of the humate was estimated by measuring the quantity of carbon dioxide (CO₂) evolved during a four‐week incubation. Results suggested a relative resistance to microbial degradation. However, results also suggested the presence of some readily decomposable C compounds associated with humate. Agricultural use of this humate reguires some modifications to produce a more reactive material. This may include a change of flocculant and a lowering of its ash content.