Soil properties influencing the denitrification potential of Flemish agricultural soils

The denitrification potential of the soil horizons between 0- and 90-cm depth of 20 agricultural fields, representative of the most frequent combinations of agricultural crops and soil textures in Flanders (Belgium), and the factors affecting the denitrification potential were studied in the laboratory under controlled conditions,. The denitrification potential in the presence of an addled soluble C and N source was measured at 15degreesC after, saturation of air-dried soil samples with water. The denitrification potential of the lower horizons was generally negligible compared to the upper horizons. The lower denitrification potential of the deeper horizons could partially be explained by their limited C availability. The denitrification potential of the upper horizons strongly depended on texture. Based on this parameter the soils could be divided into three groups: soils with a high clay content (>30% clay) were characterised by a high denitrification potential (>8.33 mug N g(-1) dry soil day(-1)); soils with medium texture had a medium denitrification potential, between 0.41 and 7.25 mug N g(-1) dry soil day(-1); and soils with a high sand content (>80% sand) had a low denitrification potential (<2.58 μg N g(-1) dry soil day(-1)). In most cases, extending the saturation period during pre-incubation increased the denitrification potential. Comparison of the denitrification potential of the upper horizons with and without addition of a soluble C source showed that the denitrification potential of the upper horizons of these soils was limited by their percentage of endogenous C. The measured denitrification potentials indicate that denitrification losses in soils high in clay content can be important when NO3 (-) concentrations are high.