title: Optimizing rice yields while minimizing yield-scaled global warming potential.
abstract: To meet growing global food demand with limited land and reduced environmental impact, agricultural greenhouse gas (GHG) emissions are increasingly evaluated with respect to crop productivity, i.e., on a yield-scaled as opposed to area basis. Here, we compiled available field data on CH4 and N2 O emissions from rice production systems to test the hypothesis that in response to fertilizer nitrogen (N) addition, yield-scaled global warming potential (GWP) will be minimized at N rates that maximize yields. Within each study, yield N surplus was calculated to estimate deficit or excess N application rates with respect to the optimal N rate (defined as the N rate at which maximum yield was achieved). Relationships between yield N surplus and GHG emissions were assessed using linear and nonlinear mixed-effects models. Results indicate that yields increased in response to increasing N surplus when moving from deficit to optimal N rates. At N rates contributing to a yield N surplus, N2 O and yield-scaled N2 O emissions increased exponentially. In contrast, CH4 emissions were not impacted by N inputs. Accordingly, yield-scaled CH4 emissions decreased with N addition. Overall, yield-scaled GWP was minimized at optimal N rates, decreasing by 21% compared to treatments without N addition. These results are unique compared to aerobic cropping systems in which N2 O emissions are the primary contributor to GWP, meaning yield-scaled GWP may not necessarily decrease for aerobic crops when yields are optimized by N fertilizer addition. Balancing gains in agricultural productivity with climate change concerns, this work supports the concept that high rice yields can be achieved with minimal yield-scaled GWP through optimal N application rates. Moreover, additional improvements in N use efficiency may further reduce yield-scaled GWP, thereby strengthening the economic and environmental sustainability of rice systems.
authors.affiliation: Department of Plant Sciences, University of California, Davis One Shields Ave, Davis, 95616, CA, USA.
authors.forename: Cameron M
authors.initials: CM
authors.lastname: Pittelkow
authors.forename: Maria A
authors.initials: MA
authors.lastname: Adviento-Borbe
authors.forename: Chris
authors.initials: C
authors.lastname: van Kessel
authors.forename: James E
authors.initials: JE
authors.lastname: Hill
authors.forename: Bruce A
authors.initials: BA
authors.lastname: Linquist
mesh_terms: D000383:Agriculture / Q000639:trends*; D000393:Air Pollutants / Q000032:analysis; D005308:Fertilizers / Q000032:analysis; D005740:Gases / Q000032:analysis; D057232:Global Warming; D017752:Greenhouse Effect; D008697:Methane / Q000378:metabolism; D009584:Nitrogen / Q000378:metabolism*; D009609:Nitrous Oxide / Q000378:metabolism; D012275:Oryza / Q000254:growth & development / Q000378:metabolism*
chemical_list: D000393:Air Pollutants; D005308:Fertilizers; D005740:Gases; D009609:Nitrous Oxide; D009584:Nitrogen; D008697:Methane
keywords: CH4; GHG emissions; N2O; greenhouse gas intensity; rice yield; synthetic N fertilizer