Lime and soil moisture effects on nitrous oxide emissions from a urine patch

Liming has been mooted as a mitigation option for lowering soil N2O emissions. This study investigated the effect of soil pH and soil water content on N2O and N-2 emissions following the addition of synthetic urine (500 kg N ha(-1)) containing N-15-labeled urea-N. Soil pH treatments ranged from 4.7 to 7.2 with either saturated or field capacity soil. Dinitrogen and N2O 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 N2O fluxes with the lowest cumulative N2O fluxes at soil pH greater than or equal to 5.9. Nitrous oxide losses ranged from < 0.1 to 0.4% of N-15 applied in the field capacity treatment but this increased to be 0.4 to 1.7% of the N-15 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 N2 fluxes increased with increasing soil pH in the saturated soil. The flux ratio of N2O-N/(N2O-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 N2O emissions from urine patches where soils are at field capacity, the resulting NO3-N will be susceptible to enhanced rates of N2O and N-2 loss if the soils are wetted up beyond field capacity.