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

ABSTRACTPasture 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 gras...