| Summary: | Processes of N transformation in soil as affected by application of the three kinds of urea fertilizers, conventional urea (U), humate-coated urea (U_HA), and urea treated with the urease inhibitor NBPT (U_UI), are examined in a model laboratory experiment. Effects of urea fertilizers on soil chemical (content of water-extractable N-NH<sub>4</sub> and N-NO<sub>3</sub>), and microbiological properties (rate of actual and potential N<sub>2</sub>O emission, basal and substrate-induced respiration, microbial biomass C, emission of ethylene) are focused to answer the following questions: (i) whether humate-coated urea has the ability to decrease N losses in soil; and (ii) how it affects soil biological activity comparable to synthetic urease inhibitor. The results showed that U_HA demonstrated advantages comparable to U in its ability to decrease N losses in soil: it increased N-NH<sub>4</sub> content by 35%, reduced nitrate content by 9%, and decreased N<sub>2</sub>O emissions by 50%. U_HA promoted basal soil respiration by 10% and the specific activity of the soil microbial community by 7%, providing the highest metabolic quotient qCO<sub>2</sub>. Comparably to NBPT-treated U, U_HA mainly shows intermediate results between U-UI and conventional U. Considering the low cost of raw humates, U-HA can be regarded as a promising tool to decrease N losses in soils.
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