Lime and Soil Moisture Effects on Nitrous Oxide Emissions from a Urine Patch

Liming has been mooted as a mitigation option for lowering soil N 2 O emissions. This study investigated the effect of soil pH and soil water content on N 2 O and N 2 emissions following the addition of synthetic urine (500 kg N ha −1 ) containing 15 N‐labeled urea‐N. Soil pH treatments ranged from 4.7 to 7.2 with either saturated or field capacity soil. Dinitrogen and N 2 O fluxes were measured from soil cores kept on water tension tables for 85 d following urine‐N addition. Soil inorganic N transformations were also monitored over time by destructively sampling soil cores on five occasions over the 85 d. At field capacity, soil pH affected the N 2 O fluxes with the lowest cumulative N 2 O fluxes at soil pH ≥ 5.9. Nitrous oxide losses ranged from <0.1 to 0.4% of 15 N applied in the field capacity treatment but this increased to be 0.4 to 1.7% of the 15 N applied in the saturated treatment. Dinitrogen fluxes were low (<23 ng N 2 –N cm −2 h −1 ) at field capacity but exceeded 4000 ng N 2 –N cm −2 h −1 under saturated conditions. Cumulative N 2 fluxes increased with increasing soil pH in the saturated soil. The flux ratio of N 2 O‐N/(N 2 O‐N + N 2 –N) remained high (0.68–0.71) under the field capacity treatment but decreased with time from 0.64 to 0.16 in the saturated treatment. This study suggests that while the use of soil liming has merit for lowering N 2 O emissions from urine patches where soils are at field capacity, the resulting NO 3 –N will be susceptible to enhanced rates of N 2 O and N 2 loss if the soils are wetted up beyond field capacity.