Mitigating N2O emissions from urine patches in pastures

Few mitigation strategies are known or tested for nitrous oxide (N2O) emissions from urine patches in pastures. We identify two such strategies and present experimental results for them: (1) avoiding detrimental soil conditions; and (2) changing urine composition through rationing. In the first strategy, soil compaction resulted in a two- to fivefold increase of emissions. Combination of urine patches with dung resulted in a comparable N2O increase. The effects of dung, seasonal variation and soil compaction could all be linked to changes in water-filled pore space (WFPS). For the second strategy, no consistent effects of urine concentration, urine volume or salt concentration could be determined. However, a shift in nitrogenous composition of urine, consistently with different diets, significantly affected N2O emissions. Increasing the hippuric acid concentration from 3% to 9% of total urine-N decreased cumulative N2O emissions from 8.4% of applied urine-N to 4.4%. We speculate that this effect is linked to an inhibitory effect of benzoic acid on the denitrification pathway. The most promising mitigation options appear to be avoiding so-called 'camping areas' in pastures and to avoid grazing under wet conditions. The possibility of decreasing N2O emissions by increasing hippuric acid concentration through diet should be explored.