Standardization of Assay Method of Urease Activity in Inceptisol

Urea is the most important nitrogen fertilizer widely used in crop production and its fate in soils is regulated largely by the soil enzyme urease. The use of precise assay method for urease is an important aspect in regulating activity of soil urease which is the most useful to improve use efficiency of urea, and minimize the problems related to use of urea. In this context, the present laboratory investigation was undertaken with the objective to standardize the assay media components of soil urease activity in Inceptisol of MPKV, Rahuri soils. The Typic Haplustept was selected as a representative of Inceptisol and used for present study of optimizing assay media components for in vivo assay method for measuring activity of urease from Inceptisol. All the assay components viz., substrate concentration (0.2 M), buffer strength (0.05 M), weight of soil (5 g), amount of toluene (0.2 ml) and incubation time (2 h) were found optimum as per Tabatabai and Bremner (1972) except THAM buffer pH. The THAM buffer with a pH 8.5 was found to be optimum for measuring the activity of urease from Inceptisol. The values of urease activity from the 2g weight of soil and 1 h incubation time also found statistically at par with values of 5 g weight of soil and 2 h incubation time, respectively. Hence, the use of 2 g soil and 1 h incubation time in assay procedure are also sufficient for measuring urease activity, if the soil sample size and time are limiting factors.