Elevating soil pH does not reduce N2O emissions from urine deposited onto pastoral soils

Urine deposited onto grazed pastures is the main source of anthropogenic nitrous oxide (N2O) in New Zealand. Low soil pH (ca 5.0) has been linked to increases in the proportion of N2O to N-2 emitted through soil denitrification. However, total denitrification rates and N2O emissions can increase with soil pH up to ca 7.0-8.0. We conducted an incubation experiment and a field study to examine the potential to mitigate total N2O emissions from urine deposition by increasing the soil pH through liming. The incubation study used three different soils where the pH was adjusted to 6.5, 6.9 and 7.4. Cumulative N2O emissions following synthetic urine application at 630 kg N ha(-1) increased with increasing soil pH. The field study, where soil pH was adjusted to 6.6, 7.0 and 7.1, had synthetic urine applied one year later at 600 kg N ha(-1). Within the pH range studied, increasing pH did not have a significant effect on N2O emissions following urine application. Both experiments suggest adjusting soil pH from ca 6 to ca 7 is not an effective tool for reducing N2O emissions from urine patches.