Abstract
Hippuric acid (HA) in cattle urine acts as a natural inhibitor of soil N 2O emissions. As HA concentration varies with diet, we determined critical HA levels. We also tested the hypothesis that the inhibition occurs because the HA breakdown product benzoic acid (BA) inhibits denitrification rates. During a 64-day incubation, we quantified emissions from artificial urine varying in HA, BA and glycine (Gly) concentrations, added to a sandy pasture soil. Increasing HA concentration from 0.4 to 5.6 mmol kg −1 soil significantly decreased the average N 2O flux by 54%. At 3.9 mmol kg −1 soil, denitrification levels were 50% reduced for BA as compared to Gly. We conclude that HA inhibits both denitrification and N 2O emission, at least partly through a BA mechanism.
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