Assay of urease activity in soils

Abstract A simple and precise method of assaying urease activity in soils is described. It involves determination of the ammonium released by urease activity when soil is incubated with tris(hydroxymethyl)aminomethane (THAM) buffer, urea solution, and toluene at 37°C for 2 h, ammonium release being determined by a rapid procedure involving treatment of the incubated soil sample with 2.5 M KC1 containing a urease inhibitor (Ag 2 SO 4 ) and steam distillation of an aliquot of the resulting soil suspension with MgO for 3.3 min. Studies reported showed that the optimal buffer pH and substrate (urea) concentration for assay of soil urease activity using THAM buffer are 9.0 and 0.02 M, respectively, and that the method described is satisfactory for assay of urease activity in ammonium-fixing soils.

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