Reducing Nitrous Oxide Emissions and Nitrate Leaching From Grazed Grasslands.

In grazed pasture systems, the nitrogen (N) contained in a cattle urine patch may be up to 1200 kg N ha^-1.  The majority of this N is in excess of plant requirements and is vulnerable to environmental loss.  In this study, cattle urine was applied at 5 rates of nitrogen, 0, 300, 500, 700 and 1000 kg N ha^-1 to soil monolith lysimeters in late autumn in Ireland in two separate years.  Dicyandiamide (DCD) nitrification inhibitor was applied in solution form at 30 kg DCD ha^-1 in two split applications following urine.  Measurements of gaseous N emissions, nitrate (NO₃^-) leaching and pasture N uptake were made for a calendar year following urine application in two consecutive experiments.  Increasing the rate of urine N applied increased the cumulative nitrous oxide (N₂O) emissions, NO₃^- leaching and pasture N uptake in years one and two, and these relationships are described.  The application of DCD reduced the cumulative N₂O emissions and NO₃^- leaching in year one but not in year two.  The pasture N uptake response to the increasing urine N rate was variable.  We suggest the use of nitrification inhibitors and the reduction of urinary N content as two mitigation strategies for N loss from grazed pasture.