RELATIONSHIPS BETWEEN DENITRIFYING ENZYME-ACTIVITY AND SOIL PROPERTIES

A short-term anaerobic assay was used to determine the potential denitrifying enzyme activity (DEA) of the top 5cm of 24 field moist soils collected in March 1989 and, in order to determine if there was a seasonal effect, on a representative subset of these soils on five occasions during the period November/December 1988 to August 1989. The 24 soils were selected to give a large variation in their physical and chemical properties. Of these properties, DEA correlated best with exchangeable Mg2+ (r = 0.85), which was itself highly correlated with indicators 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 significant 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 suggestion that annual field denitrification rates (DN) at two sites were related to DEA values. Soils from the same HOST class (Hydrology of Soil Types) appeared to have the same DEA:DN ratio. This relationship is discussed in relation to developing a Geographic Information System approach which would predict and map relative annual denitrification losses on a regional basis.