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In general, fulvic acid has a higher amount of carboxylic groups and lower average molecular weight than does humic acid. Measured average molecular weights vary with source; however, molecular weight distributions of HA and FA overlap significantly. Age and origin of the source material determine the chemical structure of humic substances.
Due to their very complex molecular structure, humic substances, including humin, do not correspond to pure substances but consist of a mixture of many compounds that remain very difficult to characterize even using modern analytical techniques. [2]
Heat is used to increase the solubility of humic acids and hence more potassium humate can be extracted. The resulting liquid is dried to produce the amorphous crystalline like product which can then be added as a granule to fertilizer. The potassium humate granules by way of chemical extraction lose their hydrophobic properties and are now ...
Fulvic acid is the genus that contains the matter that has the lowest molecular weight, is soluble in acids and alkalis, and is susceptible to microbial action. Humic acid is the genus that contains the intermediate matter that has medial molecular weight, is soluble in alkalis and insoluble in acids, and has some resistance to microbial action.
However, some authors [16] suggest that complex soil organic molecules may be much less stable than previously thought: "the available evidence does not support the formation of large-molecular-size and persistent 'humic substances' in soils. Instead, soil organic matter is a continuum of progressively decomposing organic compounds.″
They are defined operationally. The humic acids precipitate from solution at pH < 2. Likewise, the fulvic acids remain in solution. Both are complex mixtures of many organic compounds. Most aquatic NOM is fulvic acid, while a greater fraction of soil NOM (SOM) is humic acid. Humic acids generally have higher molecular weights.
At the MSU, Irina Perminova focused her research on three areas: firstly, on the studies of structure and molecular organization of humic substances, secondly, on the study of binding and detoxifying properties of humics in relation to heavy metals, polycyclic aromatic hydrocarbons, and pesticides, and, thirdly, on the search for descriptors ...
If a soil has a CEC of 20 meq and 5 meq are aluminium and hydronium cations (acid-forming), the remainder of positions on the colloids (20 − 5 = 15 meq) are assumed occupied by base-forming cations, so that the base saturation is 15 ÷ 20 × 100% = 75% (the compliment 25% is assumed acid-forming cations).