Nitrogen uptake and leaching loss of thirteen temperate grass species under high N loading

The intensification of grazed pasture systems in New Zealand has resulted in increased nitrate (NO₃⁻) leaching and associated significant reductions in water quality, resulting from high N loading in the cow urine patch. A glasshouse soil column experiment was conducted at Lincoln University examining the N uptake capacities and leaching losses of sixteen commercial and ‘weed’ pasture grasses, comprising thirteen species. Three dairy cow urine N treatments (N loading rates) were applied in May 2010: 0 (N0), 300 (N300) and 700 (N700) kg N ha⁻¹. Grass was harvested at 21-d intervals, leachates collected to quantify N leaching losses and root mass measured. Shoot yield, root mass, N uptake and N leaching loss varied significantly between species (P < 0·001) and were strongly driven by N loading rate. The highest yielding species at N700 were Lolium multiflorum ‘Feast 2’ and ‘Tama’ (782 and 743 g DM m⁻²), while Festuca arundinacea ‘Flecha’ and Lolium perenne ‘Alto' were lowest yielding (375 and 419 g DM m⁻²). Plant N uptake and root mass followed a similar trend, and only moderate increases in total plant N uptake were observed for most species when urine N application rate was increased from N300 to N700. N leaching loss was highest at N700 for F. arundinacea ‘Flecha’ (378 kg N ha⁻¹) and lowest for L. multiflorum ‘Feast 2’ and ‘Tama’ (134 and 130 kg N ha⁻¹). Strong negative linear relationships were observed between N leaching loss, plant N uptake and root mass. The results indicate that species such as L. multiflorum may play a critical role in reducing pasture N leaching losses, while traditionally sown L. perenne, and also F. arundinacea, may be less suitable