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Humic substances are organic compounds that are important components of humus the major organic fraction of soil peat and coal and also a constituent of many upland streams dystrophic lakes and ocean waterfor a long era in the 19th and 20th centuries humic substances were often viewed through a lens of acidbase theory that described humic acids as organic acids and their humic substances in the past called gelbstoff or yellow compounds are the end points of marine freshwater and soil organic degradation as polymer compounds they are highly varying combinations of organic molecules carbohydrates amino acids and fatty acids and are also highly resistant to further microbial degradationproperties of humic substances humic acids the fraction of humic substances that is not soluble in water under acidic conditions ph 2 but is soluble at higher ph valuesthey can be extracted from soil by various reagents and which is insoluble in dilute acid humic acids are the major extractable component of soil humic substanceshumic substances hs represent the organic material mainly widespread in nature hs have positive effects on plant physiology by improving soil structure and fertility and by influencing nutrient uptake and root architecture the biochemical and molecular mechanisms underlying these events are only organic matter humus humate humic acid fulvic acid and humin their importance in soil fertility and plant health dr robert e pettit emeritus associate professor texas aandm university introduction humic substances such as those listed in the above title play a vital role in soil fertility and plant nutrition

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