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Impacts of Enhanced-Efficiency Nitrogen Fertilizers on Greenhouse Gas Emissions in a Coastal Plain Soil under Cotton

Dexter B. Watts, G. Brett Runion, Katy W. Smith Nannenga, H. Allen Torbert
Journal of environmental quality 2015 v.44 no.6 pp. 1699-1710
Gossypium hirsutum, carbon dioxide, coastal plain soils, cotton, crop yield, cropping systems, global warming, greenhouse gas emissions, methane, methane production, nitrogen, nitrous oxide, polymer-coated urea, poultry manure, urea, urea ammonium sulfate
Enhanced-efficiency N fertilizers (EENFs) have the potential to increase crop yield while decreasing soil N loss. However, the effect of EENFs on greenhouse gas (GHG) emissions from different agricultural systems is not well understood. Thus, studies from a variety of locations and cropping systems are needed to evaluate their impact. An experiment was initiated on a Coastal Plain soil under cotton (Gossypium hirsutum L.) production for comparing EENFs to traditional sources. Nitrogen sources included urea, ammonia sulfate (AS), urea-ammonia sulfate (UAS), controlled-release, polymer-coated urea (Environmental Smart Nitrogen [ESN]), stabilized granular urea (SuperU), poultry litter (PL), poultry litter plus AgrotainPlus (PLA), and an unfertilized control. Carbon dioxide (CO₂), nitrous oxide (N₂O), and methane (CH₄) fluxes were monitored regularly after fertilization through harvest from 2009 to 2011 using a closed-chamber method. Poultry litter and PLA had higher CO₂ flux than other N treatments, while ESN and SU were generally lowest following fertilization. Nitrous oxide fluxes were highly variable and rarely affected by N treatments; PL and PLA were higher but only during the few samplings in 2010 and 2011. Methane fluxes were higher in 2009 (wet year) than 2010 or 2011, and N treatments had minimal impact. Global warming potential (GWP), calculated from cumulative GHG fluxes, was highest with PL and PLA and lowest for control, UAS, ESN, and SU. Results suggest that PL application to cotton increases GHG flux, but GHG flux reductions from EENFs were infrequently different from standard inorganic fertilizers, suggesting their higher cost may render them presently impractical.