Potential for forage diet manipulation in New Zealand pasture ecosystems to mitigate ruminant urine derived N₂O emissions: a review

© 2016 The Royal Society of New Zealand. Nitrous oxide (N₂O) emissions from agricultural soils account for more than 10% of New Zealand’s greenhouse gas emissions. Livestock urine deposition drives N₂O losses from these soils. It has been speculated that non-urea nitrogen compounds (UNCs) in ruminant urine could reduce or inhibit urine patch N₂O emissions. However, we hypothesise that UNCs will have no effect on N₂O emissions due to their potentially rapid degradation by plants and soil microbes. Our review suggests that plant secondary metabolites (PSMs) are more likely to perform a role in reducing N₂O emissions since many PSMs have known antimicrobial properties. Aucubin, found in Plantago, and isothiocyanates, found in Brassica, have been shown to inhibit a key step in N₂O production. Future studies should explore this promising research gap by evaluating forages for potential inhibitory PSMs, assessing whether PSMs are excreted in urine after consumption, and determine whether excretal PSM concentrations are sufficient to reduce N₂O emissions