The increased stability of humic substances reduces the emission of C-CO2,19 i.e., oxidation of the same. Chemical stability of C occurs with formation of humic substances, this process can be estimated by the increased concentration of free radicals of semiquinones type. 24 thus we suggest the existence of a relationship between the formal potential of the electrode (FandºH) of SH and radical content semiquinones, since these are the main responsible for the transfer of electrons. 25 however, according the values obtained for the c/n ratio