Influence of liming-induced pH changes on nitrous oxide emission, nirS, nirK and nosZ gene abundance from applied cattle urine in allophanic and fluvial grazed pasture soils

The influence of soil pH changes by liming on denitrification and denitrifier gene abundance under different biogeochemical conditions by amending two contrasting soils with water, cattle urine (600 mg N kg−1 soil) and urine + dicyandiamide (DCD) (10 mg kg−1 soil) and incubating at 10 °C and 15 °C was evaluated. Liming increased N2O emission, denitrification rate and denitrifier gene abundance in both soils. The increase in N2O and denitrification with liming was higher in fluvial soil (24% increase in N2O and 22% increase in denitrification) than in allophanic soil (16% in N2O and 19% increase in denitrification). There was more N2O coming from urine applied to limed soil than that from urine to un-limed soil. Addition of DCD with urine reduced both N2O emission and denitrification; the reduction was greater in limed soil than in un-limed soil. Results of quantitative polymerase chain reaction (qPCR) of bacterial denitrifier genes (nirS, nirK and nosZ genes) indicate that liming-induced soil pH changes increased denitrifier gene abundance and caused more complete bacterial denitrification in urine-amended soils. These results suggest that liming grazed pasture soils induces complete denitrification, which may mitigate N2O emissions.