Mitigating N2O emissions from urine patches in pastures
Groenigen, J.W. van; Kool, D.M.; Oenema, O.; Kuikman, P.J.
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.