REDUCING NITRATE LOSSES FROM SIMULATED GRAZING ON GRASSLAND LYSIMETERS IN IRELAND USING A NITRIFICATION INHIBITOR (DICYANDIAMIDE)

Nitrate (NO3-) pollution of water is a serious environmental problem, as NOT can contribute to the eutrophication of surface waters, and high levels may cause methaemoglobinaemia in formula-fed infants. Grassland agriculture is a major source of diffuse NO3- pollution, with much of this NO3- originating from urine deposited by grazing animals. The research objective was to determine the effectiveness of a nitrification inhibitor, dicyandiamide (DCD), in reducing NO3- leaching under Irish dairy farming conditions. Urine was applied in autumn to undisturbed monolith lysimeters to replicate an average cattle urination (21 of 8.6g N l(-1) urine), or 344kg N ha(-1) equivalent. Nitrogen (N) fertiliser was applied at 141kg ha(-1) and 291kg ha(-1). DCD was applied in autumn and spring. The total annual NO3- - N losses from urine patches on three soils ranged from 16kg to 204kg NO3- - N ha(-1). Peak concentrations on the non-urine treatments did not exceed 6.1 mg NO3- - N l(-1), but reached 17.1-148.6mg NO3- N l(-1) when urine was applied. DCD reduced the total NO3- - N losses from urine treatments on the lighter soils by 38%-42%, and reduced peak NO3- - N concentrations by over 50%. This trial has shown that DCD has the potential to significantly reduce NOT leaching losses from grazed grassland in Ireland.