Abstract Rapid assays for urea hydrolysis and for the oxidation of NH4+ to NO2– and NO3– are required for extensive studies of these processes in potting media. Methods originally developed for use with field soils were evaluated and modified for use with soilless media. Effects of urea concentration, buffer pH, and incubation temperature on rates of urea hydrolysis were tested with two media. Response to these variable was less pronounced in soilless potting media than in field soils. Urea hydrolysis can be conveniently assayed in soilless media under the following conditions: 5 mol urea/m3 medium, Tris buffer pH 8.0, 37°C. Rates of NH4+ and NO2– oxidation were estimated from the accumulation of NO2– in samples incubated for 0 to 24 hr with 4 mol NH4+/m3 medium as substrate in 1.0 mM phosphate buffer, pH 7.0, with or without 20 mol NaClO3/m3 medium. The rate of NO2– accumulation in the presence of ClO3–, an inhibitor of NO2– oxidation, estimates NH4+ oxidation, and the slope of the difference in NO2– between samples with and without ClO3– estimates the rate of NO2– oxidation. Although ClO3– does not completely inhibit NO2– oxidation in one of the two media tested, the method is useful for comparison of nitrification activity in potting media.