M. Abdalla, M. Wattenbach, P. Smith, P. Ambus, M. Jones and M. Williams, Application of the DNDC model to predict emissions of N2O from Irish agriculture., Geoderma, 151, 2009, 327, 337
A mechanistic model that describes N fluxes from the soil, DeNitrification DeComposition (DNDC), was tested against seasonal and annual data sets of nitrous oxide flux from a spring barley field and a cut and grazed pasture at the Teagasc Oak Park Research Centre, Co. Carlow, Ireland. In the case of the arable field, predicted fluxes of N2O agreed well with measured fluxes for medium to high fertilizer input values (70 to 160 kg N ha-1) but described poorly measured fluxes from zero fertilizer treatments. In terms of cumulative flux values, the relative deviation of the predicted fluxes from the measured values was a maximum of 6% for the highest N fertilizer inputs but increased to 30% for the medium N and more than 100% for the zero N fertilizer treatments. A linear correlation of predicted against measured flux values for all fertilizer treatments (r2 = 0.85) was produced, the equation of which underestimated the seasonal flux by 24%. Incorporation of literature values from a range of different studies on arable and pasture land did not significantly affect the regression slope. DNDC describe poorly measured fluxes of N2O from reduced tillage plots of spring barley. Predicted cumulative fluxes of N2O on plots disc ploughed to 10cm, underestimated measured values by up to 55%.
For the cut and grazed pasture the relative deviations of predicted to measured fluxes were 150 and 360% for fertilized and unfertilized plots. This poor model fit is considered due to DNDC overestimating the effect of initial soil organic carbon (SOC) on N2O flux, as confirmed by a sensitivity analysis of the model. As the arable and grassland soils differed only in SOC content, reducing SOC to the arable field value significantly improved the fit of the model to measured data such that the relative deviations decreased to 9 and 5% respectively. Sensitivity analysis highlighted air temperature as the main determinant of N2O flux, an increase in mean daily air temperature of 1.5oC resulting in almost 90% increase in the annual cumulative flux. Using the Hadley Centre Global Climate Model data (HCM3) and the IPCC emission scenarios A2 and B2, DNDC predicted increases in N2O fluxes of approximately 30% (B2) and 60% (A2) from the spring barley field and approximately 20% (A2 and B2) from the cut and grazed pasture by the end of this centaury (2061-2090).
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