Phytotesting of soils with traditional and new forms of nitrogen fertilizers was carried out in the laboratory at the D.N. Pryanishnikov All-Russian Research Institute of Agrochemistry in 2024-2025. Prolonged-release urea-formaldehyde fertilizers (UF), which contain fast- and slow-soluble nitrogen, were tested. The length of the roots of spring wheat and white mustard seedlings in sod-podzolic soil and leached chernozem after composting fertilizers for 28 and 50 days was estimated. When applying conventional carbamide, regardless of the type of soil and crop, with an increase in the composting period, a stronger inhibition of plant root growth was observed. The decomposition products of fertilizers had a less pronounced negative effect on white mustard. In general, according to experience, the phytotoxicity of UFs was lower compared to standard carbamide, as well as lower in leached chernozem compared to sod-podzolic soil. The stimulating effect of prolonged forms of nitrogen fertilizers during prolonged composting was revealed in the chernozem on white mustard plants by 9; 63 and 137%, respectively, and on UF-3 spring wheat plants by 28%. The study of the dynamics of fertilizer conversion showed that the content of ammonium nitrogen in the soil decreased to the initial level on the 21st day and ammonia poisoning could not cause phytotoxicity. It is shown that the accumulation of nitric acid as a result of nitrification led to significant acidification of the soil. In the carbamide variant, on days 21-28, there was a more pronounced decrease in the reaction of the soil environment to the pHKCl to 4.6-4.7 units, which is 0.6-0.7 units. lower than in the original soil, when applying UFs, the pHKCl was significantly higher and amounted to 4.9-5.0 units.