Effect of calcareous and non-calcareous amendments on fertilizer-induced N2O emissions in a clay loam in SE Norway.

Despite ample evidence since the 1950s that the N2O product ratio of soil denitrification decreases with increasing pH, no systematic research has been carried out to investigate liming as mitigating tool. Here we report a N2O flux experiment with soils three years after applying calcareous (dolomite, calcite) and non-calcareous (norite, larvikite, olivine) limes in a field experiment in SE Norway. To create homogeneous conditions with respect to drainage, soils from field plots were excavated, homogenized and packed into freely draining pots. After sowing the pots to ryegrass, N2O fluxes were monitored after subsequent addition of NH4NO3 (160 kg N ha-1), NaNO3 (110 kg N ha-1) and simulated ploughing in late autumn, i.e. mixing the grass sward and adding additional KNO3 (5 g N m-2). Whereas the flux response to NH4NO3 was independent of liming treatment (plausibly due to dry summer conditions with no denitrification), N2O fluxes after KNO3 addition showed lowest fluxes in dolomite (90.2 g N m-2 in 22 weeks) and marble (80.8 g N m-2 in 22 weeks) treatments. The incorporation of grass in autumn was followed by diurnal freezing- and thawing, eliciting N2O fluxes of up to 6677 µg N m-2 h-1, likely originating from denitrification. Under these conditions a clear pH dependency emerged with 50% lower cumulative fluxes (over 22 weeks) in calcite treated soils (pH 6.7) as compared with acid control (pH 4.9) and soils with siliceous amendments, which did not show any pH response. Our results suggest that liming acidic soils can be used to mitigate N2O emissions during "hot moments" of vigorous denitrification. However, possibilities for precision liming should be investigated in order to reduce the byproduct of CaCO3 dissolution, CO2 which is a potent greenhouse gas. Site-specific fertilization and liming could regulate emissions derived from denitrification and lower N2O emissions overall. [ABSTRACT FROM AUTHOR]