Summary
Urea hydrolysis was measured in two separate sets of experiments. (1) Nine soil (0–15 cm) samples were treated with 200 μg of urea-N g−1 dry soil and incubated (at 37°C) at 50 per cent of the water holding capacity. Samples were periodically analysed for the remaining urea-N. The urease activity (time in hoursrequired to hydrolyse half the applied urea-N) was determined to be 5.8 to 15.2 hours in the various soils, which appeared to associate principally with the organic carbon content of the soils (r=−0.80**). (2) Three soils were treated with 25 to 2000 μg urea-N g−1 dry soil amounting to 0.9 to 72.0 mM urea in 1∶1 soil: solution. The system was buffered at pH 7.2 and agitated for 5h when the remaining urea-N was determined. The values of Km and Vmax were computed by two methods (i) from the integrated form of the Michaelis-Menten equation based on the results of the first study, and (ii) from the Michaelis-Menton equation based on urea hydrolysis in the second study. The integrated method appeared to be more suitable for enzyme kinetic studies in soil systems where the Km and Vmax values bore close relationship (r=−0.88**).
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Beri, V., Goswami, K.P. & Brar, S.S. Urease activity and its Michaelis constant for soil systems. Plant Soil 49, 105–115 (1978). https://doi.org/10.1007/BF02149912
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DOI: https://doi.org/10.1007/BF02149912