Humic Substances as Agronomic Inputs in Biological Agricultural Systems : a Review-Wet Chemistry vs . Complex Geobiological Systems

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The lower molecular weight of fulvic acid is sometimes said to account for its greater biological availability , That is somewhat correct , but very vague because the industry has not agreed on standardized molecular weights for fulvic acid , Defining humic acid , fulvic acid and humin by their molecular weights is a controversial concept .

Some wet chemistry techniques can be used to characterize different

humic materials , For example , the carbon/oxygen ratio is used by some to determine the presence of functional groups , There may be some merit to thisas functional groups are high in oxygen content , The difficulty with wet chemistry techniques is that it rarely mimics the real environment in which these materials are expected to perfrom .

Humic substances change their structure depending on pH and the type of metals present , High pH makes humic substances apen up their long chain polymers and low pH makes them close , In the presence of toxic metals , humic substances remove the metals from the surrounding environment by forming insoluble aggregated spheres around them .

Humic substances are polymer-like molecules that demonstrate self-organization , The bi-layers formed by humic substances to surround otherwise insoluble minerals are reminiscent of the way all living things utilize biochemical reactions in cellular systems , showing a strong resemblance to the biological mechanisms of living membranes , as described in college text booxs , such as Voet , 1995 . Humic substances are more like living creatures than chemical entities , but they dont reproduce .

Slight changes in pH will actually cause the humic polymers to fracture , breaking up the original molecules , The fractured molecules are then free to associate with numerous other free radicals , metals or impurities , Humic substances are made up of hundreds of different molecules of many different sizes with many ways to orient themselves by twisting , bending , compressing and expanding , They are held together very loosely by weak forces in a colloidal state .

Any change in solution pH , concentration or the presence of metal ions , especially calcium ions , will cause huge changes in the physical make up of the humic molecules , Even slight changes cause the molecutes to change in orders of magnitude , Rapid changes in molecular structures are not peculiar to just humic substances , Water molecules change their structure 10,000,000,000,000, times a second , AIthough water is an extremely simple molecule , the determination of its structure at any given instant is still somewhat unknown , The amazing complexity of humic substances may forever keep their structures a secret .

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