Nitrate (NO3-) leaching from agricultural land and the contamination of surface and ground waters is a major environmental concern around the globe. In New Zealand, the dominant land use is grazed pastures where animals graze outdoor pastures all year round. In intensively grazed pasture systems (e.g. dairy pasture), most of the nitrate leached is from nitrogen deposited in animal urine patch areas. Here we report the use of a nitrification inhibitor ‘eco-n' (active ingredient: dicyandiamide, DCD) to treat grazed pasture soils to reduce nitrate leaching. The effectiveness of eco-n in reducing nitrate leaching was determined using large (50-80 cm diameter; 70-120 cm deep) undisturbed monolith lysimeters. The soils used were Lismore stony silt loam (Udic Haplustept loamy skeletal) and Templeton fine sandy loam (Udic Haplustepts). Nitrous oxide (N2O, a potent greenhouse gas) emissions were also measured on these lysimeters using closed chamber methods. Pasture was cut at typical grazing intervals and dry matter yield recorded. By treating grazed pasture soils with the eco-n nitrification inhibitor, NO3- leaching can be significantly reduced (Di and Cameron, 2002, 2004). For example, treatment of urine patches with eco-n on the Templeton soil reduced NO3--N leaching losses from 85 to 20-22 kg N ha-1 yr-1 (equivalent to 74-76% reductions). N2O emissions from the urine patches from the Lismore soils were reduced by as much as 75% (Di and Cameron, 2003). Pasture yield was increased significantly by about 33% from the urine patch areas on the lysimeters. Therefore, treating grazed pasture soil with the eco-n nitrification inhibitor not only provides environmental benefits by reducing NO3- leaching and nitrous oxide emissions, but also provides agronomic benefits. Acknowledgments: We thank Ravensdown Fertiliser Co-operative Ltd and NZ Foundation for Research, Science and Technology for funding, and Trevor Hendry, Steve Moore, Neil Smith, Nigel Beale and Hamish Masters for technical support. References: Di, H.J. and Cameron, K.C. (2002). The use of a nitrification inhibitor, dicyandiamide (DCD), to reduce nitrate leaching and nitrous oxide emissions in a simulated grazed and irrigated grassland. Soil Use Manag. 18: 395-403. Di, H.J. and Cameron, K.C. (2003). Mitigation of nitrous oxide emissions in spray-irrigated grazed grassland by treating the soil with dicyandiamide, a nitrification inhibitor. Soil Use Manag. 19: 184-290. Di, H.J. and Cameron, K.C. (2004). Treating grazed pasture soil with a nitrification inhibitor, eco-nTM, to decrease nitrate leaching in a deep sandy soil under spray irrigation. N. Z. J. Agric. Res. 47(3): 351-361.