Evaluation of nitrogen release of enhanced fertilizers in two different soil types through laboratory incubation and leaching studies

Nitrogen (N) release performance and leaching studies were performed on four urea-based fertilizer formulations: market urea, technical urea, a mixture of urea and gums, and a urea-gypsum cocrystal (URCASU). Nitrogen release was assessed through a 56-day laboratory soil incubation experiment in clay loam and silty loam soil texture. On each sampling day, both organic and inorganic forms of N were measured. Two fertilizer placement methods were used: surface application and incorporation into the soil. In addition to N release experiments, flow-cell leaching studies were conducted on samples collected on day 14. The results from the soil incubation studies showed that both urea+gums and URCASU released N significantly more slowly than market urea. Pairwise comparison results indicated that URCASU released significantly less N than market urea in the clay loam fertilizer incorporated, silt loam fertilizer incorporated, and silty loam fertilizer placed on surface. In clay loam soil, the highest concentration of ammonium for all fertilizers was observed on day 7, while nitrate peaked on day 28. In silt loam soil, ammonium levels for all fertilizers were highest on day 1, with nitrate reaching its maximum also on day 28. Additionally, the urea+gums formulation performed significantly better than market urea in silt loam (incorporated). However, no significant difference in N release was observed between URCASU and the urea+gums treatment across both soil types and placement methods. In summary, the leaching studies demonstrate the slow release behavior of the enhanced urea formulations in both soil types tested in this study. • N release from new fertilizer formulations tested in clay and silty loam soil • Urea – gypsum cocrystal (URCASU) compacts remained stable up to 56 days in soil • Fertilizer placement had no significant effect on nitrogen release • URCASU and urea+gums are promising enhanced-efficiency fertilizers