A review of the effect of autumn nitrogen fertiliser on pasture nitrogen concentration and an assessment of the potential effects on nitrate leaching risk

Abstract

The aim was to test the hypothesis that nitrogen (N) fertiliser applied in autumn increases N leaching by increasing pasture N concentration (Nconc) and thus increasing partitioning of excretal N to urine. A review of past data showed that N fertiliser application generally had only a small effect on pasture Nconc, on average. The general effect was ±5% or less for single applications of 50 kg N/ha or less, compared with nil N fertilised pasture, depending on the season. Based on this, we estimated that the increase in pasture Nconc from autumn fertiliser is less important for nitrate leaching risk than the extra forage grown, and the resultant extra N consumed and excreted as a result of the applied fertiliser N. However, if the period between fertiliser application and grazing is short, the elevation in Nconc is likely to be larger with a greater influence on partitioning to urinary N. Keywords: Nitrogen, fertiliser, pasture nitrogen concentration, urine