Fertilization Systems and Effects of Their Long-Term Application on the Fractional Composition of Mineral Phosphates and Mobile Phosphorus Content in the Profile of Sod–Podzolic Soils

This paper examines the effects of the long-term application of fertilizers on the phosphate regime in a sod–podzolic heavy loamy soil in the western piedmont of the Ural Mountains. The study was conducted to assess the influence of the organic (manure at doses of 10 and 20 t/ha of arable land per year), mineral (mineral fertilizers in amounts equivalent to the NPK content in manure at doses of 10 and 20 t/ha per year), and organomineral (manure at doses of 5, 10, and 20 t/ha per year in combination with mineral fertilizers in amounts equivalent to the NPK content in manure) fertilization systems on the fractional composition of mineral phosphates (determined using the Ginzburg–Lebedeva method) and mobile phosphorus content in the soil. The 1-m soil layer was studied in the framework of a long-term, outdoor stationary eight-field crop rotation experiment launched in 1968. It is established that the Fe–P (45%) and Ca–P (42%) fractions predominate in the composition of mineral phosphates in the sod–podzolic soil. The long-term systematic application of fertilizers results in a significant increase in content of the most mobile fraction: calcium and ferrous phosphates (Ca–PI and Fe–P) in the soil. The organic, mineral, and organomineral fertilization systems statistically significantly increase the mobile phosphorus content in the arable layer (from 125 to 192–368 mg/kg). The mobile phosphorus reserves in the arable layer increase by 1.7–3.0 times, while those in the 1-m soil layer by 1.1–1.6 times. The maximum effect on the soil phosphate regime parameters was noted in the variant involving the application of manure at a dose of 20 t/ha per year in combination with NPK in an equivalent amount. The observed changes in the fractional composition of phosphates and mobile phosphorus content are consistent with the existing balance of this element in the soil.