Quantifying Uncertainties in N2O Emission Due to N Fertilizer Application in Cultivated Areas

Abstract

Nitrous oxide (N2O) is a greenhouse gas with a global warming potential approximately 298 times greater than that of CO2. In 2006, the Intergovernmental Panel on Climate Change (IPCC) estimated N2O emission due to synthetic and organic nitrogen (N) fertilization at 1% of applied N. We investigated the uncertainty on this estimated value, by fitting 13 different models to a published dataset including 985 N2O measurements. These models were characterized by (i) the presence or absence of the explanatory variable “applied N”, (ii) the function relating N2O emission to applied N (exponential or linear function), (iii) fixed or random background (i.e. in the absence of N application) N2O emission and (iv) fixed or random applied N effect. We calculated ranges of uncertainty on N2O emissions from a subset of these models, and compared them with the uncertainty ranges currently used in the IPCC-Tier 1 method. The exponential models outperformed the linear models, and models including one or two random effects outperformed those including fixed effects only. The use of an exponential function rather than a linear function has an important practical consequence: the emission factor is not constant and increases as a function of applied N. Emission factors estimated using the exponential function were lower than 1% when the amount of N applied was below 160 kg N ha−1. Our uncertainty analysis shows that the uncertainty range currently used by the IPCC-Tier 1 method could be reduced.

Global metaanalysis of the nonlinear response of soil nitrous oxide (N 2 O) emissions to fertilizer nitrogen

“…Philibert et al (30) show an improved CI for the range of nonlinear and linear models. When not accounting for parameter uncertainty, the lower boundary of Philibert et al (31) coincides with ours, whereas the upper boundary is more conservative than ours for N-input levels >150 kg·ha −1 . Parameter uncertainty widens the CI in the work by Philibert et al (31) and brings our estimate entirely within the boundary for N inputs up to 250 kg·ha −1 .…”

“…We determined the mean quadratic model and used a resampling procedure to obtain the 95% CI for all of the site-years in our dataset, excluding sites with N-fixing crops and bare soil. We compared this CI with 95% CIs for IPCC tier 1 methodology and for the range of six models used by Philibert et al (31), including and not including parameter uncertainty. Selecting only studies with four or more N-input levels in our dataset, we performed a procedure described by Kim et al (25) to classify all site-years into categories of linear, faster than linear (exponential), and slower than linear (hyperbolic) N 2 O emission increases with N input.…”

Nitrous oxide emissions from a peatbog after 13 years of experimental nitrogen deposition

“…This response was greater than the default 1 % IPCC emission factor, and comes close to 8.5 % (with the appropriate unit conversion). The relationship may not be linear (Philibert et al, 2012), and the general additive mixed model (GAMM) was fitted to allow for non-linearity in the fixed effects. However, the exact form of the response to NH 3 deposition was not well constrained by the data, especially at the lower values, and a simple linear fit was justified (Fig.…”

Assessment of uncertainties in greenhouse gas emission profiles of livestock sectors in Africa, Latin America and Europe

“…CO 2 emissions from fuel use and fertilizer production were calculated according to Lesschen et al (2011). Emissions from on farm energy use were based on Opio et al (2013) and Macleod et al (2013), who derived emission factors in terms of emission and/or energy per unit of animal product. CO 2 emissions from pesticide use were based on country average pesticide use from FAOSTAT and a general emission factor of 10.97 kg CO 2 -eq/kg active ingredient from BioGrace (2011).…”

“…This resulted in a lower uncertainty in N 2 O soil emissions for Europe. Philibert et al (2012) and Leip (2010) suggested that the ranges of the IPCC N 2 O emission factors might be overestimated with the Tier 1 approach. This implies that our uncertainty estimates for N 2 O emissions in Latin America and Africa could be overestimated.…”