Nitrification results in underestimation of soil urease activity as determined by ammonium production rate

The majority of soil urease activity measurements have been based on the rate of ammonium production under optimal conditions. However, such procedures do not exclude ammonium consumption by the nitrification process. The purpose of this study was to determine the percentage of soil urease activity that is underestimated due to soil nitrification. Six soils with diverse properties were incubated using a standard procedure for measuring soil urease activity. The dynamics of nitrite and nitrate were observed during the incubation. Our results showed that the percentage of underestimation ranged from 7.38% to 15.97%, depending on soil types and whether or not a buffer was used. We recommend that nitrification be taken into account when soil urease activity is assayed by the ammonium production rate method.