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Nitrogen inputs and losses from white clover/ryegrass pastures grazed by dairy cows were measured over three years in a farmlet experiment near Hamilton, New Zealand. Three farmlets received nominal rates of nitrogen fertilizer of 0, 200 or 400 kg N ha-1 year-1. Nitrate leaching from the free-draining soil averaged 40, 81 and 152 kg N ha-1 year-1, respectively. The other main nitrogen losses/removals were in milk and transfer of excreta to lanes and the milking shed. Gaseous nitrogen losses were small but increased up to 5-fold with nitrogen fertilizer application. Groundwater nitrate-N concentrations increased with nitrogen application to an average of 19 mg 1-1 in the 400 N farmlet. Data are discussed in relation to that for average dairy farms in New Zealand and European countries, and to the environmental implications for theResource Management Act of New Zealand. [ABSTRACT FROM AUTHOR]