title: Maximum soil organic carbon storage in Midwest U.S. cropping systems when crops are optimally nitrogen-fertilized.
abstract: Nitrogen fertilization is critical to optimize short-term crop yield, but its long-term effect on soil organic C (SOC) is uncertain. Here, we clarify the impact of N fertilization on SOC in typical maize-based (Zea mays L.) Midwest U.S. cropping systems by accounting for site-to-site variability in maize yield response to N fertilization. Within continuous maize and maize-soybean [Glycine max (L.) Merr.] systems at four Iowa locations, we evaluated changes in surface SOC over 14 to 16 years across a range of N fertilizer rates empirically determined to be insufficient, optimum, or excessive for maximum maize yield. Soil organic C balances were negative where no N was applied but neutral (maize-soybean) or positive (continuous maize) at the agronomic optimum N rate (AONR). For continuous maize, the rate of SOC storage increased with increasing N rate, reaching a maximum at the AONR and decreasing above the AONR. Greater SOC storage in the optimally fertilized continuous maize system than in the optimally fertilized maize-soybean system was attributed to greater crop residue production and greater SOC storage efficiency in the continuous maize system. Mean annual crop residue production at the AONR was 22% greater in the continuous maize system than in the maize-soybean system and the rate of SOC storage per unit residue C input was 58% greater in the monocrop system. Our results demonstrate that agronomic optimum N fertilization is critical to maintain or increase SOC of Midwest U.S. cropland.
authors.affiliation: Department of Agronomy, Iowa State University, Ames, Iowa, United States of America.
authors.forename: Hanna J
authors.identifier: http://orcid.org/0000-0002-7715-373X
authors.initials: HJ
authors.lastname: Poffenbarger
authors.affiliation: Department of Agronomy, Iowa State University, Ames, Iowa, United States of America.
authors.forename: Daniel W
authors.initials: DW
authors.lastname: Barker
authors.affiliation: Department of Agricultural and Biosystems Engineering, Iowa State University, Ames, Iowa, United States of America.
authors.forename: Matthew J
authors.initials: MJ
authors.lastname: Helmers
authors.affiliation: Department of Agronomy, Iowa State University, Ames, Iowa, United States of America.
authors.forename: Fernando E
authors.initials: FE
authors.lastname: Miguez
authors.affiliation: National Laboratory for Agriculture and the Environment, United States Department of Agriculture-Agricultural Research Service, Ames, Iowa, United States of America.
authors.forename: Daniel C
authors.initials: DC
authors.lastname: Olk
authors.affiliation: Department of Agronomy, Iowa State University, Ames, Iowa, United States of America.
authors.forename: John E
authors.initials: JE
authors.lastname: Sawyer
authors.affiliation: Department of Environmental Systems Science, Swiss Federal Institute of Technology, ETH-Zurich, Zurich, Switzerland.
authors.forename: Johan
authors.initials: J
authors.lastname: Six
authors.affiliation: Department of Agronomy, Iowa State University, Ames, Iowa, United States of America.
authors.forename: Michael J
authors.initials: MJ
authors.lastname: Castellano
mesh_terms: D002244:Carbon; D000069599:Crop Production / Q000379:methods*; D005308:Fertilizers; D015146:Midwestern United States; D009584:Nitrogen; D012987:Soil; D013025:Glycine max / Q000254:growth & development*; D003313:Zea mays / Q000254:growth & development*
chemical_list: D005308:Fertilizers; D012987:Soil; D002244:Carbon; D009584:Nitrogen