Nitrate leaching losses are lower from ryegrass/white clover forages containing plantain than from ryegrass/white clover forages under different irrigation

The aim of this research was to assess the potential of using perennial ryegrass ( Lolium perenne ) and white clover ( Trifolium repens ) forages containing plantain ( Plantago lanceolata L.) (PRGWC + Plantain) to mitigate nitrate (NO 3 − ) leaching in grazed grassland. Lysimeter studies were carried out to determine NO 3 − leaching losses from the PRGWC + Plantain forage, compared with the standard perennial ryegrass and white clover forage (PRGWC) under three different irrigation conditions (flood, rotorainer and pivot). Fresh dairy cow urine (700 kg N ha −1 ) was applied to these lysimeters in early summer (December) and late summer (February). Nitrogen (N) dynamics and the abundance of ammonia oxidising bacteria (AOB) and archaea (AOA) were also determined in companion mini‐plots alongside the lysimeters. Nitrate leaching losses from the PRGWC + Plantain forage were 82% lower than those from the PRGWC forage when urine was applied in December and 74% less when urine was applied in February ( P < .05). This was possibly due to the release of biological nitrification inhibitors by plantain which slowed down the nitrification process and this, combined with a lower drainage volume, was largely responsible for the lower NO 3 − leaching losses in the PRGWC + Plantain forages. The three different irrigation schemes did not significantly affect NO 3 − leaching losses under the two forage types. These results demonstrate the potential of using PRGWC + Plantain forages as an effective mitigation option for NO 3 − leaching in grazed grasslands.