『Abstract
Models are increasingly used to examine the potential impacts
of management and climate change in agriculture. Our aim in this
paper was to assess the applicability of the field-Denitrification
DeComposition (DNDC) model in Irish agriculture. This study provides
the results of that evaluation, which is a prerequisite for using
the model for assessing management impacts in the future. The
DNDC model 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 (70-160 kg N ha-1) but poorly described those
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. There is a linear correlation
of predicted against measured flux values for all fertilizer treatments
(r2 = 0.85) but the model underestimated the seasonal
flux by 24％. Incorporation of literature values from a range of
different studies on arable and pasture land did not significantly
improve the regression. The description by DNDC for measured fluxes
of N2O from reduced tillage plots was poor
with underestimation of up to 55％.
For the cut and grazed pasture the relative deviation of predicted
to measured fluxes were 150 and 360％ for fertilized and unfertilized
plots. A sensitivity analysis suggests that the poor model fit
is due to DNDC overestimating WFPS and the effect of initial soil
organic carbon (SOC) on N2O flux. As the
arable and grassland soils differed only in SOC content, reducing
SOC of the grassland field to that of 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 1.5℃ resulting in almost a 65％ increase in the annual cumulative
flux. This is interesting as with future global warming, N2O flux from the soil will have a strong positive
feedback. It can be concluded that DNDC is unsuitable for predicting
N2O from Irish grassland due to its overestimation
of WFPS and effect of SOC on the flux.
Keywords: Nitrous oxide; DNDC model; Arable; Pasture; Irish agriculture』
1. Introduction
2. Materials and methods
2.1. Experiments
2.2. Field N2O fluxes
2.3. Soil moisture
2.4. DNDC model
3. Results and discussion
3.1. Arable field
3.2. Pasture field
3.3. Sensitivity analysis
4. Conclusions
Acknowledgement
References