title: Global metaanalysis of the nonlinear response of soil nitrous oxide (N2O) emissions to fertilizer nitrogen.
abstract: Nitrous oxide (N2O) is a potent greenhouse gas (GHG) that also depletes stratospheric ozone. Nitrogen (N) fertilizer rate is the best single predictor of N2O emissions from agricultural soils, which are responsible for ∼ 50% of the total global anthropogenic flux, but it is a relatively imprecise estimator. Accumulating evidence suggests that the emission response to increasing N input is exponential rather than linear, as assumed by Intergovernmental Panel on Climate Change methodologies. We performed a metaanalysis to test the generalizability of this pattern. From 78 published studies (233 site-years) with at least three N-input levels, we calculated N2O emission factors (EFs) for each nonzero input level as a percentage of N input converted to N2O emissions. We found that the N2O response to N inputs grew significantly faster than linear for synthetic fertilizers and for most crop types. N-fixing crops had a higher rate of change in EF (ΔEF) than others. A higher ΔEF was also evident in soils with carbon >1.5% and soils with pH <7, and where fertilizer was applied only once annually. Our results suggest a general trend of exponentially increasing N2O emissions as N inputs increase to exceed crop needs. Use of this knowledge in GHG inventories should improve assessments of fertilizer-derived N2O emissions, help address disparities in the global N2O budget, and refine the accuracy of N2O mitigation protocols. In low-input systems typical of sub-Saharan Africa, for example, modest N additions will have little impact on estimated N2O emissions, whereas equivalent additions (or reductions) in excessively fertilized systems will have a disproportionately major impact.
authors.affiliation: W. K. Kellogg Biological Station, Michigan State University, Hickory Corners, MI 49060; andDepartment of Plant, Soil, and Microbial Sciences and Great Lakes Bioenergy Research Center, Michigan State University, East Lansing, MI 48824 iurii.shcherbak@gmail.com.
authors.forename: Iurii
authors.initials: I
authors.lastname: Shcherbak
authors.affiliation: W. K. Kellogg Biological Station, Michigan State University, Hickory Corners, MI 49060; andDepartment of Plant, Soil, and Microbial Sciences and Great Lakes Bioenergy Research Center, Michigan State University, East Lansing, MI 48824.
authors.forename: Neville
authors.initials: N
authors.lastname: Millar
authors.affiliation: W. K. Kellogg Biological Station, Michigan State University, Hickory Corners, MI 49060; andDepartment of Plant, Soil, and Microbial Sciences and Great Lakes Bioenergy Research Center, Michigan State University, East Lansing, MI 48824.
authors.forename: G Philip
authors.initials: GP
authors.lastname: Robertson
mesh_terms: D017954:Africa South of the Sahara; D001272:Atmosphere; D002244:Carbon / Q000737:chemistry / Q000378:metabolism; D018556:Crops, Agricultural / Q000254:growth & development / Q000378:metabolism; D017752:Greenhouse Effect; D009584:Nitrogen / Q000737:chemistry / Q000378:metabolism; D009586:Nitrogen Fixation; D009609:Nitrous Oxide / Q000737:chemistry / Q000378:metabolism; D012987:Soil / Q000737:chemistry
chemical_list: D012987:Soil; D002244:Carbon; D009609:Nitrous Oxide; D009584:Nitrogen
keywords: agriculture; bioenergy; fertilizer response; greenhouse gas emissions; greenhouse gas mitigation