Reactive nitrogen in a clay till hill slope field system

To assess the contribution of reactive nitrogenfrom groundwater to surface waters, we need more knowledge on how reactive nitrogenbehaves in the glacial tillsystems underlying many agricultural fields. Groundwater sampled from suction cupsand piezometersplaced in the glacial tillunderlying a winter wheat field shows the nitrate concentration in water leaching to deeper than 2 m below ground surface (mbg) is ~ 60 mg L−1. Within 5 mbg, all of the nitrate is removed and this appears to take place within a redoxzone rather than at a sharp redoxfront. Ammonium released from the tillis negligible. A 2D dataset reveals that the depth to the redoxzone undulates between 3 and 5 mbg, perhaps a result of local variations in infiltration. It appears that the nitrate is generally reduced by the oxidation of pyrite and locally by organic matter in lenses within the till.