Modeling the Effects of Fertilizer Application Rate on Nitrous Oxide Emissions

Abstract

The attribution of N2O emission factors to N inputs from chemical fertilizers requires an understanding of how those inputs affect the biological processes from which these emissions are generated. We propose a detailed model of soil N transformations as part of the ecosystem model ecosys for use in attributing N2O emission factors to fertilizer use. In this model, the key biological processes—mineralization, immobilization, nitrification, denitrification, root, and mycorrhizal uptake—controlling the generation of N2O were coupled with the key physical processes—convection, diffusion, volatilization, dissolution—controlling the transport of the gaseous reactants and products of these biological processes. Physical processes controlling gaseous transport and solubility caused large temporal variation in the generation and emission of N2O in the model. This variation limited the suitability of discontinuous surface flux chambers measurements used to test modeled N2O emissions. Continuous flux measurements using micrometeorological techniques were better suited to the temporal scales at which variation in N2O emission occurred and at which model testing needed to be conducted. In a temperate, humid climate, modeled N2O emissions rose nonlinearly with fertilizer application rate once this rate exceeded the crop and soil uptake capacities for added N. These capacities were partly determined by history of fertilizer use, so that the relationship between N2O emissions and current N inputs depended on earlier N inputs. A scheme is proposed in which N2O emission factors rise nonlinearly with fertilizer N inputs that exceed crop plus soil N uptake capacities.

Nitrogen fertilizer management for nitrous oxide (N2O) mitigation in intensive corn (Maize) production: an emissions reduction protocol for US Midwest agriculture

“…1). Non-linear relationships have also been found in corn and wheat systems in Ontario and Alberta, (Grant et al 2006;Ma et al 2009). Emissions of N 2 O may therefore exhibit a threshold response related to crop N requirement and the magnitude of N input (Erickson et al 2001).…”

“…Evidence from high resolution N fertilizer gradients in Michigan (McSwiney and Robertson 2005;Hoben et al 2010, in review;Millar et al 2010, in review) suggest that N 2 O emissions increase exponentially with increasing fertilizer N rate, particularly at high rates that exceed the ecosystem (crop+soil) N uptake capacity (Grant et al 2006). In a 3 year continuous corn experiment with nine fertilizer N rates from 0 to 291 kg N ha −1 yr −1 , McSwiney and Robertson (2005) discovered a non-linear relationship between N rate and emissions of N 2 O, with fluxes remaining low and relatively stable at low N rates, and rapidly increasing at N rates beyond which crop yield was maximized.…”

Effect of temporal resolution on N2O emission inventories in Dutch fen meadows

“…Flechard et al [2007] observed N 2 O emission factors, which were consequently smaller for dry years than for other years. For boreal sub humid climates, Grant et al [2006] already advised to decrease emission factors for dry years.…”

Responses of N<sub>2</sub>O and CH<sub>4</sub> fluxes to fertilizer nitrogen addition rates in an irrigated wheat-maize cropping system in northern China

“…The response curves of N 2 O emissions as a function of the fertilizer rate are not common. Only a few studies that have utilized fertilized treatments with more than two nitrogen levels could obtain functional relationships between N 2 O emissions and fertilizer rates (Grant et al, 2006;Mosier et al, 2006;Halvorson et al, 2008;Hoben et al, 2011). When fertilizer rates are in excess of the amount required to optimize crop growth, N 2 O emissions are stimulated (McSwiney and Robertson, 2005;Zebarth et al, 2008).…”

“…When fertilizer rates are in excess of the amount required to optimize crop growth, N 2 O emissions are stimulated (McSwiney and Robertson, 2005;Zebarth et al, 2008). Some studies reported the N 2 O emissions exponentially increased with fertilizer rates (Grant et al, 2006;Hoben et al, 2011), but because of the complexity of agricultural management and natural conditions, the functional relationships may not be nonlinear. Hoben et al (2011) obtained both linear and nonlinear relationships for different years and sites with on-farm maize crops in the US Midwest.…”