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.
Highlights
Nitrous oxide (N2O) is a greenhouse gas (GHG) with a global warming potential approximately 298 times greater than that of CO2 [1]
Database The dataset is a global compilation of nitrous oxide (N2O) and nitric oxide (NO) emissions extracted from peer-reviewed publications appearing between 1979 and 2004, established by Stehfest and Bouwman [10]
As we focused on calculation of the emission factor associated with fertilizer applications in agricultural fields (EF), we excluded the following experiments from the initial dataset: (i) 418 experiments carried out in natural areas, (ii) 360 experiments including measurements of NO emission only, (iii) 57 experiments on organic soils, (iv) 25 experiments including the use of chemicals or additives considered to inhibit nitrification, (v) 8 experiments in grazing systems, (vi) 38 experiments in which the amounts of applied N exceeded 500 kg N ha21 yr21
Summary
Nitrous oxide (N2O) is a greenhouse gas (GHG) with a global warming potential approximately 298 times greater than that of CO2 [1]. N2O emissions increased by almost 17% from 1990 to 2005 [2]. The nitrogen (N) cycle is complex and N2O emissions are determined by many factors [3]. N2O is emitted as a result of nitrification (oxidation of ammonia) and denitrification (nitrate reduction), and these processes are influenced by applications of mineral N fertilizer and manure to agricultural soils [4,5]. N applications are recognized as the major source of anthropogenic nitrous oxide emission [6,7]. N2O emissions are influenced by other management practices (e.g., tillage [8]), soil and climate characteristics (e.g. soil water content) [9,10,11,12,13]
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