RELATIONSHIPS BETWEEN DENITRIFYING ENZYME-ACTIVITY AND SOIL PROPERTIES

A short-term anaerobic assay was used to determine the potential denit rifying enzyme activity (DEA) of the top 5cm of 24 field moist soils c ollected in March 1989 and, in order to determine if there was a seaso nal effect, on a representative subset of these soils on five occasion s during the period November/December 1988 to August 1989. The 24 soil s were selected to give a large variation in their physical and chemic al properties. Of these properties, DEA correlated best with exchangea ble Mg2+ (r = 0.85), which was itself highly correlated with indicator s of soil organic matter such as cation exchange capacity and organic carbon. Dry matter was negatively correlated with DEA (r = -0.75) and reflected the moisture content of the soil at the time of collection. When Mg2+ was added to various soils in laboratory experiments, no sig nificant effect on DEA was observed, indicating that the effect of Mg2 + on DEA was indirect. The DEA value was also found to vary with time of year, being highest during the summer months. There was some sugges tion that annual field denitrification rates (DN) at two sites were re lated to DEA values. Soils from the same HOST class (Hydrology of Soil Types) appeared to have the same DEA:DN ratio. This relationship is d iscussed in relation to developing a Geographic Information System app roach which would predict and map relative annual denitrification loss es on a regional basis.