Ribwort plantain inclusion reduces nitrate leaching from grass-clover swards; A multi-year five soil study

Reducing nitrate leaching and addressing water quality concerns is a challenge in grazed pasture systems globally. Recent single soil, single region studies have indicated that the inclusion of ribwort plantain (Plantago lanceolate L.) in pasture swards can reduce nitrate-N (NO₃^--N) leaching. The present two-year five-soil lysimeter study tests the potential of ribwort plantain inclusion in grass-clover (Lolium perenne L. and Trifolium repens L.) swards to reduce NO₃^--N leaching across a range of soils. The inclusion of plantain at 30 % reduced NO₃^--N loss in free-draining soils by 7–59 kg NO₃^--N ha⁻¹ (by 32–74 %, mean 56 %) in year one and by 12–54 kg NO₃^--N ha⁻¹ (93–99 %, mean 96 %) in year two. In poorly drained soils the loss reduction ranged from 2 to 6 kg NO₃^--N ha⁻¹ (3–10 %, mean 6 %) in year one and by 29–36 kg NO₃^--N ha⁻¹ (97–98 %, mean 97 %) in year two. Increasing plantain inclusion to 50 % reduced NO₃^--N loss in the free-draining soils by 11–91 kg NO₃^--N ha⁻¹ (50–95 %, mean 78 %) in year one and by 13–56 kg NO₃^--N ha⁻¹ (97–98 %, mean 98 %) in year two. In poorly drained soils the NO₃^--N loss reduction ranged from 12 to 15 kg NO₃^--N ha⁻¹ (18–24 %, mean 21 %) in year one and by 29–36 kg NO₃^--N ha⁻¹ (98 %) in year two. Plantain inclusion reduced drainage water volume by 1–16 %, potentially contributing to nitrate-N loss mitigation. Plantain inclusion reduced drinking water NO₃^--N maximum allowable concentration (MAC) exceedances in leachate from 28 in grass-clover to seven with 30 % plantain inclusion and four with 50 % plantain inclusion. Much of the benefit of plantain inclusion was achieved at the 30 % plantain rate in grass-clover pastures. Overall, across a broad range of soils, the inclusion of plantain in grass-clover swards was shown to be an effective tool for reducing nitrate-leaching losses in pasture systems.