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

ABSTRACT

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 N₂ 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.

KEYWORDS:

• Denitrification
• lime
• inorganic-N
• urea
• CEC

Acknowledgements

We would like to thank Wayne Worth, Tom Orchiston, Priscila Simon for assisting in the field and laboratory, and Esther Meenken and Peter Johnstone for statistical analysis.

Disclosure statement

No potential conflict of interest was reported by the author(s).

Additional information

Funding

This work was funded by the New Zealand Ministry for Primary Industries through the New Zealand Fund for Global Partnerships in Livestock Emissions Research to support the objectives of the Livestock Research Group of the Global Research Alliance on Agricultural Greenhouse Gases and the European Research Area Network Cofund for Monitoring & Mitigation of Greenhouse gases from Agri- and Silvi-culture (Agreement number: S7-SOW16-ERAGAS-MAGGEpH). SG was also funded through a University of Otago Doctoral Scholarship.