Abstract
AbstractNitrous oxide (N2O) is a potent greenhouse gas and major component of the net global warming potential of bioenergy feedstock cropping systems. Numerous environmental factors influence soil N2O production, making direct correlation difficult to any one factor of N2O fluxes under field conditions. We instead employed quantile regression to evaluate whether soil temperature, water‐filled pore space (WFPS), and concentrations of soil nitrate () and ammonium () determined upper bounds for soil N2O flux magnitudes. We collected data over 6 years from a range of bioenergy feedstock cropping systems including no‐till grain crops, perennial warm‐season grasses, hybrid poplar, and polycultures of tallgrass prairie species each with and without nitrogen (N) addition grown at two sites. The upper bounds for soil N2O fluxes had a significant and positive correlation with all four environmental factors, although relatively large fluxes were still possible at minimal values for nearly all factors. The correlation with was generally weaker, suggesting it is less important than in driving large fluxes. Quantile regression slopes were generally lower for unfertilized perennials than for other systems, but this may have resulted from a perpetual state of nitrogen limitation, which prevented other factors from being clear constraints. This framework suggests efforts to reduce concentrations of in the soil may be effective at reducing high‐intensity periods—”hot moments”—of N2O production.
Highlights
Nitrous oxide (N2O) is a major contributor to global radiative forcing (Forster et al, 2007) and is currently the single most important ozone‐depleting substance in the atmosphere (Portmann, Daniel, & Ravishankara, 2012)
Agricultural soils are responsible for 77% of N2O emissions in the United States (U.S Environmental Protection Agency, 2018) and
Many studies report markedly different N2O emissions levels among cropping systems, with lower emissions frequently observed in perennial, species‐rich, or minimally fertilized systems (Gelfand, Shcherbak, Millar, Kravchenko, & Robertson, 2016; Niklaus, Wardle, & Tate, 2006; Oates et al, 2016; Stehfest & Bouwman, 2006)
Summary
Nitrous oxide (N2O) is a major contributor to global radiative forcing (Forster et al, 2007) and is currently the single most important ozone‐depleting substance in the atmosphere (Portmann, Daniel, & Ravishankara, 2012). Fossil fuel displacement for many bioenergy feedstock cropping systems (Crutzen, Mosier, Smith, & Winiwarter, 2008; Robertson, Paul, & Harwood, 2000), making their management and mitigation of N2O production a major part of assessing net long‐term environmental impact (Gelfand & Robertson, 2015). Many studies report markedly different N2O emissions levels among cropping systems, with lower emissions frequently observed in perennial, species‐rich, or minimally fertilized systems (Gelfand, Shcherbak, Millar, Kravchenko, & Robertson, 2016; Niklaus, Wardle, & Tate, 2006; Oates et al, 2016; Stehfest & Bouwman, 2006) It is less clear whether these differences primarily derive from environmental conditions (e.g., higher soil N) or how agroecosystems respond to those conditions, with major implications for predicting their behavior under novel conditions.
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