<Li> Fulvic acid is the group which contains the materials that have the lowest molecular weight, and are soluble in acids and alkali, and susceptible to microbial attack . </Li> <Li> Humic acid group contains the intermediate materials, with medium molecular weight, soluble in alkali, but insoluble in acid, and intermediate resistance to microbial attack . </Li> <Li> Humin is the generic name for the materials with highest molecular weight, that are darkest in color, insoluble in acid and alkali, and with the most resistance to microbial attack . </Li> <P> Soil plays a major role in the global carbon cycle, with the global soil carbon pool estimated at 2500 gigatons . This is 3.3 times the size of the atmospheric pool (750 gigatons) and 4.5 times the biotic pool (560 gigatons). The pool of organic carbon, which occurs primarily in the form of SOM, accounts roughly 1550 gigatons of the total global C pool, with the remainder accounted for by soil inorganic carbon (SIC). The pool of organic C exists in dynamic equilibrium between gains and losses; soil may therefore serve as either a sink or source of C, through sequestration or greenhouse gas emissions, respectively, depending on exogenous factors . </P>

Where is the most organic material found in soil