Abstract
The relevance of this study is associated with the intensive use of mineral fertilizers, during which up to 40–70% of nitrogen is lost through leaching and volatilization, leading to reduced fertilizer efficiency and increased environmental risks. Therefore, the development of environmentally safe fertilizers with controlled nutrient release represents an important scientific challenge. The research aim was to quantitatively evaluate the effect of starch-to-urea ratios on the physicochemical, mechanical, and phytotoxic properties of fertilizers. The research objectives included the preparation of fertilizer samples with different mass ratios of starch and urea (20/80, 40/60, 50/50, and 80/20) and the determination of granule strength, abrasive wear losses, urea leaching rates, and phytotoxicity levels. The scientific novelty of the research lies in substantiating the role of starch as a biopolymer matrix and the effect of a 2% potassium hydroxide solution on starch gelatinization and granule structure formation. It was demonstrated that granule strength increased with higher starch content: at a 20/80 ratio, strength ranged from 0.5 to 0.7 MPa, whereas at 50/50 and 80/20 ratios it reached 1.0–1.2 MPa. Abrasive wear losses decreased from 10–12% to 1–2%. Urea leaching within 1 hour reached 55–65% in samples containing 80% urea, while formulations with higher starch content showed a 5–6% reduction in leaching. Phytotoxicity assessment using garden cress (Lepidium sativum L.) revealed high seed germination rates (95–100%) and root growth stimulation by 12–27% at a 25% soil extract concentration. The obtained results confirm the high potential of starch–urea-based fertilizers as environmentally safe, mechanically stable, and slow-release nitrogen fertilizers for sustainable agricultural applications.