Assessment and Improvement of the Efficiency of Nitrogen Use on Commercial Dairy Farms

Dairy farming systems have a low efficiency of converting nitrogen (N) into milk protein, due to the many transfers which occur in the production process. Losses of N from the system can be detrimental to the environment and represent wasted inputs. At SAC, in a systems research project, management changes achieved increases in nitrogen efficiency (milk N output/ N inputs) (NE) from 23 to 34% in a grass-clover based system (GC), and 13 to 21% in a purchased fertiliser based system (GN) (Leach & Roberts, 2002). Nitrogen surplus (NS = N inputs - N output in sold produce) was reduced from 184 to 90 kg N/ha in GC and from 369 to 258 kg N/ha in GN. This work was then incorporated into a participatory research project, to obtain data on N balances in commercial dairy systems and investigate the effects of suggesting management changes to improve NE.