Mobile forms of phosphorus and iron compounds in chernozem-like soils in the northern part of the Tambov plain

Moisture content and redox conditions are factors determining the dynamics of the content of mobile phosphorus in chernozem-like soils moistened and waterlogged by groundwater and surface water. When the moisture content increases and oxidizing conditions are still present in soils belonging to the chernozem type that contain a high concentration of calcium phosphates, the latter transform from apatite into more mobile forms, Ca-PI and Ca-PII. In chernozem-like soils with a high concentration of iron phosphates under reducing conditions, the amount of phosphorus extracted with 0.1 N H₂SO₄ increases owing to the transition of iron phosphates into a mobile state. Precipitations enriching the soil with atmospheric oxygen promote the increase in the value of the oxidation-reduction potential (Eh), thereby decreasing the mobility of iron phosphates.