STUDY OF THE CHEMICAL AND MINERALOGICAL COMPOSITION OF THE COMPLEX-MIXED FERTILIZERS OBTAINED ON THE BASIS OF VERMICULITE AND SELECTION OF THE OPTIMAL COMPOSITION

Abstract

This study investigates the technology of obtaining multifunctional, multicomponent complex-mixed organomineral fertilizers based on local mineral and secondary raw materials—namely vermiculite, biohumus, and phosphogypsum—combined with mineral salts (ammophos and urea). In the first series of experiments, the effect of varying phosphogypsum and vermiculite contents (from 6 to 28%) on the fertilizer properties was evaluated, while the second series analyzed the transition dynamics and ratios between the organic (biohumus) and mineral phases. Based on a comprehensive evaluation of agrochemical and physico-mechanical properties, samples No. 6 and No. 7 from the first series were selected as the optimal compositions. These optimal formulations exhibit high nutrient concentrations (total P₂O₅ 11.2–12.3%, K₂O 2.42–2.75%, total nitrogen 10.2–14.3%), an adequate supply of calcium and sulfur derived from phosphogypsum (CaO 7.2–12.52%, SO₃ 15.2–25.32%), and exceptionally high phosphorus bioavailability with citrate-soluble P₂O₅ degrees reaching 97.76–98.84%.