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Inorganic orthophosphates and condensed phosphates strongly affected the acidic-basic properties of soil humus substances, which was expressed by the degree of their hydrolyzability in alkaline, acidic, and neutral media. The humus substances modified by phosphates were characterized by increased electron donor (basic, after Lewis) properties, as compared to the native substances, due to accumulation of C=C-bonds. They exerted an especially strong dissolving effect on Fe- and Al-containing soil minerals and had a greater affinity to exogenous Zn. The pattern of distribution of phosphorus in ortho- and pyrophosphates among a fraction of humus substances was studied.