Italian ryegrass swards reduce N leaching via greater N uptake and lower drainage over perennial ryegrass cultivars varying in cool season growth rates

Pasture mitigation strategies are needed to reduce the negative effects of nitrate (NO₃⁻) leaching from intensive pastoral livestock production systems. We explored the capability of pasture grasses with different cool season (winter–early spring) growth rates to reduce NO₃⁻ leaching and increase N uptake. Following a single urine application of 700 kg N ha⁻¹, NO₃⁻ leaching loss and N uptake by Italian ryegrass and four perennial ryegrass cultivars of varying seasonal growth (heading dates from –7 to +20 days), either undersown with/without Italian ryegrass, were quantified in a 12 month lysimeter study. Italian ryegrass cv. Tabu had lower NO₃⁻ –N leaching loss and drainage, and greater N uptake and DM yield than perennial ryegrass varieties. Italian ryegrass total N leaching loss (143 kg N ha⁻¹ yr⁻¹) was 46–33% less (P < .05) than early and mid-season maturing Tyson, Arrow and AberDart perennial ryegrass. Italian ryegrass total N uptake (463 kg N ha⁻¹) was 1.2–1.4 times greater than all other grass sward types. Overall, perennial ryegrass pure swards had similar N uptake and N leaching. Late-season maturing One 50 perennial ryegrass showed significantly reduced (P < .05) total N leaching loss. Undersowing Italian ryegrass into established perennial ryegrass swards resulted in lower NO₃⁻leaching and greater N uptake than non-undersown perennial ryegrass swards, though not significant. Results confirm Italian ryegrass is a useful pasture grass option for reducing annual N leaching loss. Cool season perennial ryegrass varieties appear not to influence soil N uptake and leaching loss