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 K m and decreased V max , behaving as mixed inhibitors to soil urease. With increasing temperature, the K m and V max values increased significantly. With incubation time, K m decreased, while V max significantly increased. Compared with control, treatment HQ decreased soil urease thermodynamic parameters Ea, ΔH, and Q 10 , but in PPD and NBPT treatments, the parameters increased slightly. The Q 10 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.

No tillage is being popularized for the rainfed maize production in Northeast China. In order to evaluate its effects on the nutrient contents and enzymatic characteristics in upland soils of Northeast China, surface (0-20 cm) meadow brown soil samples were collected from the plots under no tillage and conventional tillage in a 7-year field experiment under maize cropping in Shenyang, with the soil pH, contents of total C, N, P and S and available N, activities of α-and β-galactosidase, α-and β-glucosidase, urease, protease, phosphomonoesterase, phosphodiesterase, and arylsulphatase, and kinetic parameters of β-glucosidase, protease, phosphomonoesterase, phosphodiesterase, and arylsulphatase determined. Comparing with conventional tillage, no tillage increased the contents of soil total C, N, and S and available N, the activities of test enzymes, and the V max /K m of soil urease, protease, and phosphomonoesterase, but decreased the activity of soil α-galactosidase and the V max /K m of soil β-glucosidase significantly. All the results suggest that long term no tillage for the maize production on meadow brown soil of Northeast China could enhance soil nutrients storage and the turnover of soil N and P, but had definite negative effects on the transformation of soil C.