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TECHNICAL REPORTS

Fertilizer Application Timing Influences Greenhouse Gas Fluxes Over a Growing Season

USDA-ARS, Northern Great Plains Research Lab., 1701 10th Ave SW, Mandan, ND 58554. The U.S. Department of Agriculture, Agricultural Research Service is an equal opportunity/affirmative action employer and all agency services are available without discrimination. Mention of commercial products and organizations in this manuscript is solely to provide specific information. It does not constitute endorsement by USDA-ARS over other products and organizations not mentioned

^* Corresponding author (Rebecca.phillips{at}ars.usda.gov).

Received for publication November 14, 2008. Microbial production and consumption of greenhouse gases (GHG) is influenced by temperature and nutrients, especially during the first few weeks after agricultural fertilization. The effect of fertilization on GHG fluxes should occur during and shortly after application, yet data indicating how application timing affects both GHG fluxes and crop yields during a growing season are lacking. We designed a replicated (n = 5) field experiment to test for the short-term effect of fertilizer application timing on fluxes of methane (CH₄), carbon dioxide (CO₂), and nitrous oxide (N₂O) over a growing season in the northern Great Plains. Each 0.30-ha plot was planted to maize (Zea mays L.) and treated similarly with the exception of fertilizer timing: five plots were fertilized with urea in early spring (1 April) and five plots were fertilized with urea in late spring (13 May). We hypothesized time-integrated fluxes over a growing season would be greater for the late-spring treatment, resulting in a greater net GHG flux, as compared to the early-spring treatment. Data collected on 59 dates and integrated over a 5-mo time course indicated CO₂ fluxes were greater (P < 0.0001) and CH₄ fluxes were lower (P < 0.05) for soils fertilized in late spring. Net GHG flux was also significantly affected by treatment, with 0.84 ± 0.11 kg CO₂ equivalents m^–2 for early spring and 1.04 ± 0.13 kg CO₂ equivalents m^–2 for late spring. Nitrous oxide fluxes, however, were similar for both treatments. Results indicate fertilizer application timing influences net GHG emissions in dryland cropping systems.

Abbreviations: GHG, greenhouse gases • WFPS, water-filled pore space