Nitrogen use efficiency and manure management practices in contrasting dairy production systems

Abstract

As dairy operations continue to intensify world-wide, with greater nitrogen (N) inputs contributing to increasing productivity, the reliance on N recycling is decreasing, leading to larger N surpluses and environmental losses. We investigated feed N use efficiency (FNUE) and milk urea N concentrations (MUN) of the lactating herd, and manure management practices on 29 grazing and confinement-based commercial dairy farms in Victoria, Australia and Wisconsin, USA, to assess opportunities to increase N efficiency and reduce N losses. There was a similar variation in FNUE on dairy farms in Victoria and Wisconsin, ranging from 15 to 35%. FNUE and MUN levels demonstrated opportunities to improve diet management and reduce N intakes on many farms in both regions. In summer, Victorian dairy farms were significantly ( P < 0.001) less efficient in converting feed N into milk, even though low N intakes were determined on 7 farms. Grazing-based systems had between 51 and 89% of excreted N directly deposited on to pasture soils, while on confinement-based farms between 57 and 100% of excreted N was deposited in areas with routine collection, which was reapplied to cropped land. Irrespective of the production system, only a small proportion of available land was used to apply collected manure. On a large number of farms in both regions, substantial amounts of excreted N were deposited in non-productive areas with no collection, potentially increasing the risk of N losses in surface runoff. We suggest that simple on-farm assessments can be used in contrasting dairy production operations internationally to assess feed and manure N management practices, which will assist in developing appropriate industry benchmarks and benefit productivity and environmental outcomes.