Fertiliser strategies for improving nitrogen use efficiency in grazed dairy pastures

Evidence from farm level studies indicates that there is potential to improve nitrogen (N) use efficiency of the predominately pasture-based dairy farms in Australia. This is possible via several ways which includes modifying the timing and rates of N fertiliser applied to pasture. Traditionally fertiliser strategies have been based on a “recipe” approach where N fertiliser, primarily urea, is applied a set rate following grazing. The aim of this study was to compare the pasture dry matter response, N loss and response rate of fertiliser strategies which used increasing knowledge of plant and soil conditions in different ways. The study was conducted under grazing conditions using the biophysical model, DairyMod and repeated at several locations and farming systems in the dairy regions of Australia. In comparison to set rates this study showed that strategic approaches to N fertiliser have the potential to be more efficient in N use and lower both N inputs and N losses with little impact of pasture production. This was evident across all seasons and locations studied. Strategies that used the plant N status to trigger fertiliser timing and rates were more efficient and had lower environmental N losses than those that used fixed rates or soil N information. Fertilising per plant N requirements was the most efficient – and therefore should be the priority for development – particularly in view of the greater expense of fertilisers that are slow release. Precision fertiliser management strategies have the value in terms of reducing fertiliser use and loss during autumn and to a lesser extent in summer, with the least value in winter. However, for the strategies to be properly evaluated for pasture based dairy farms with grazing, a whole farm analysis needs to be conducted that incorporates other sources of feed. This is a necessary inclusion in any subsequent studies.