Environmental impacts of different nitrogen inputs on dairy farms and implications for the Resource Management Act of New Zealand

Abstract

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 l −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 the Resource Management Act of New Zealand.