Abstract

In recent years, there has been increased concern about the contamination of waterways with nutrients, in particular the nitrate-N (NO₃⁻) leached from pastoral farms (Ministry for the Environment 2020). At higher concentrations (>11.3 mg N/L), nitrate-N can be hazardous to human health and aquatic life (Di & Cameron 2002). Nitrate-N leaching is known to be high under dairy cattle grazing, however, there has been little research to quantity nitrate-N leaching under sheep and cattle grazing, particularly in recent times. This study compared nitrate-N leaching under sheep and beef cattle grazing perennial ryegrass/white clover. It also investigated whether mixing Italian ryegrass with brassica can mitigate nitrate-N leaching relative to a brassica monoculture crop under sheep grazing. The measured rates of nitrate-N leaching were also compared with predicted values using Overseer. Twenty plots were sown in four treatments each with five replicates: sheep grazing perennial ryegrass/white clover, sheep grazing turnips/Italian ryegrass, sheep grazing kale, and rising one-year cattle (R1) grazing perennial ryegrass/white clover. Measured leaching losses under all treatments were small and there was no significant difference (P>0.05) in the nitrate-N leaching flux between treatments. The Overseer estimates of nitrate-N leaching were greater than the observed values. Further, Overseer modelling also predicts that there would not be differences in the leaching losses observed under sheep and R1 cattle grazing.

Algharibeh, F.F.M., Cranston L.M., Millner J.P., Kenyon P.R., Morel P.C.H., and Horne D.J.

Hamilton, Volume 85, Hamilton, 16-19, 2025