Assessment and improvement of the efficiency of nitrogen use on commercial dairy farms

Nine dairy farmers participated in a project which ran over a four year period from 1997 to 2001, with the aim of improving nitrogen use efficiency (NE) and reducing nitrogen surpluses. Results from systems research and the disadvantages of large nitrogen losses and low NE to the economics of the farm business and the environment were outlined and possible mitigation strategies were discussed with the farmers during visits by a dairy consultant. Initial nitrogen use efficiency (nitrogen output/nitrogen input) ranged from 10% to 23% and nitrogen surplus from 259 to 785 kg N ha¹. During the project nitrogen efficiency improved by an average of 5.4% and nitrogen surpluses reduced by an average of 186 kg N ha¹. The largest changes in nitrogen output per hectare were due to changes in stocking rate rather than changes in milk yield per cow or milk protein content. Nitrogen input was dominated by nitrogen fertilizer input, which for farms applying more than 150 kg N ha¹accounted for between 41% and 85% of total nitrogen input. Reduction in mineral nitrogen fertilizer use was the main way that farmers improved nitrogen efficiency and reduced nitrogen surpluses.