Can nitrogen use efficiency strategies enhance the sustainability and production efficiency of temperate grazing dairy systems?

This was examined through four separate investigations, namely, 1) a retrospective analysis of the incorporation of the legume white clover (Trifolium repens L.; WC) into PRG swards within a high N input grazing dairy system (Chapter 4), 2) a systems experiment investigating PRG-only and PRG-WC swards at two levels of N fertiliser (150 and 250 kg N/ha; Chapter 5), 3) supplementing PRG diets with a rumen protected protein source compared to a rumen degradable protein source within a low CP concentrate supplement (Chapter 6) and 4) comparing herbage production of different N fertiliser types and rates (Chapter 7).

Chapter 4 interrogated an existing database, comprised of results from a larger, overall systems experiment, that showed fluctuations in WC content in PRG swards within a high N input (250 kg N/ha, annually) grazing dairy system. In Chapter 5, a separate grazing experiment was established that compared both herbage and milk production of PRG-only and PRG-WC swards at 150 and 250 kg N/ha. Chapter 6 investigated the impact of supplementation of differing protein sources at low amounts on milk production and N use efficiency.