The potential role of the nitrification inhibitor DCD for reducing nitrate leaching from grazed grassland

Introduction Reducing nitrate leaching from agricultural sources to sensitive receiving waters continues to be a national priority. The latest EPA report states that groundwater and estuarine quality continues to decline with 2% of groundwater supplies exceeding 50 mg L -1 NO3 and 19% of estuaries being classified as eutrophic. The Nitrate Action plan and the Good Agricultural Practice for Protection of Waters Regulations 2006 (SI 378 of 2006) have led to the introduction of compulsory measures for farmers to improve nitrogen utilisation efficiency and control losses to water. Nitrification inhibitors have been shown to increase nitrogen utilisation by plants through slowing down the rate at which ammonium is converted to nitrate. Nitrification inhibition also has the environmental benefits of reducing nitrate leaching and nitrous oxide emissions from soils (e.g. Di and Cameron, 2004). The objective of this lysimeter experiment was to assess the effect of DCD (dicyandiamide), a commercially used nitrification inhibitor, on nitrate leaching from Irish grassland soils after urine and fertiliser applications.