Ruminant urine patch nitrification and N2O flux: effects of urine aucubin rate in a laboratory trial
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Livestock urine deposition onto grazed New Zealand pastures drives soil nitrous oxide (N2O) emissions. Urine patch N2O emissions can be reduced by inhibiting nitrification, a key urine patch nitrogen (N) transformation pathway. Aucubin, a secondary metabolite found in the pasture herb species plantain (Plantago lanceolata), is a potential nitrification inhibitor and could be excreted in urine by animals grazing plantain. In this laboratory trial, three rates of aucubin application (10, 50, and 100% of the highest theoretical aucubin excretion rate from cows grazing 100% plantain pasture) were added to urine and assessed for their potential to inhibit nitrification and subsequent N2O emissions. Significantly reduced N2O flux and soil concentrations, aligned with significantly increased soil and soil surface pH, indicated that aucubin inhibited nitrification from 5 to 17 days after urine application. However, this period of inhibition was not sufficient to reduce overall N2O emissions during the 35 day experiment.