Preparation and Characterization of Functional Composite Polymeric Media Based on Potassium Polyacrylate Hydrogel for Root-Zone Applications

Functional composite polymeric media based on superabsorbent hydrogels are promising materials for controlled water retention and ion-exchange nutrient release in root-zone applications. This study investigates the design, fraction-dependent properties, and functional performance of composite polymeric media based on potassium polyacrylate hydrogel (B 415 K) combined with vermicompost and perlite. Hydrogel fractions (fine, medium 0.5–1.5 mm, and coarse) were characterized by optical microscopy and Raman spectroscopy (785 nm). Raman analysis revealed six characteristic bands (1086, 710, 673, 531, 282, and 157 cm−1) for the medium fraction, and swelling ratios followed the order: fine (23.4 g/g) > medium (19.1 g/g) > coarse (12.7 g/g). The medium fraction provided the optimal balance between hydration, structural integrity, and sorption of organic growth stimulants, establishing structure–property–performance relationships for the composite polymeric media. Composite media were prepared at a dry-component ratio of hydrogel:vermicompost:perlite = 1:40:20, and their water retention, pH buffering, electrical conductivity, and K+ release dynamics were evaluated over 21 days. The composite medium maintained stable moisture at 68–72% of full water-holding capacity, whereas the control decreased to 55–60%. Exchangeable K+ remained at 120–135 mg/L throughout the experiment, whereas in the control it decreased from 100 to 65 mg/L, confirming the stimuli-responsive ion-exchange function of the polyacrylate network. The performance of the polymeric media was demonstrated using garden strawberry (Fragaria × ananassa ‘Alba’) rosettes as a model root-zone application: rooting reached 100% in the composite medium vs. 86% in the control and 92% in pure hydrogel; total root system length increased 1.6-fold, and root dry biomass increased by 45%. Field validation confirmed the stability of the polymeric medium under open-ground conditions, with 96.7% survival and a 30% reduction in irrigation frequency. The developed composite polymeric media provide sustained water retention and potassium release without additional mineral fertilizers, demonstrating the potential of rational design of functional polymeric materials for root-zone application.