Kinetic and Thermodynamic Behaviors of Soil Urease as Affected by Urease Inhibitors

The kinetic characteristics of soil urease have attracted great attention, but little information was available on its kinetic and thermodynamic behaviors as affected by urease inhibitors and temperature. With black soil (Pachic Udic Mollisol) in Heilongjiang Province of Northeast China as a test soil, an incubation test was conducted to investigate the effect of urease inhibitors (hydroquinone, HQ; phenyl phosphorodiamidate, PPD; N-(n-Butyl) thiophosphoric triamide, NBPT) on kinetic and thermodynamic behaviors of soil urease at 10oC, 20oC and 30°C. The results showed that all tested inhibitors increased Km and decreased Vmax, behaving as mixed inhibitors to soil urease. With increasing temperature, the Km and Vmax values increased significantly. With incubation time, Km decreased, while Vmax significantly increased. Compared with control, treatment HQ decreased soil urease thermodynamic parameters Ea, ΔH, and Q10, but in PPD and NBPT treatments, the parameters increased slightly. The Q10 and ΔH of soil urease decreased slightly with increasing temperature. Among test inhibitors, PPD and NBPT were more effective in influencing the kinetic and thermodynamic behaviors of urease in black soil. The variations in kinetic and thermodynamic parameters indicated that the effects of urease inhibitors on soil urease are greater on kinetic behaviors rather than on thermodynamic ones.