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ARS Home » Midwest Area » St. Paul, Minnesota » Soil and Water Management Research » Research » Publications at this Location » Publication #268680
Title: Broadcast urea reduces N2O emissions but increases NO emissions compared with conventional and shallow-applied anhydrous ammonia in a coarse-textured soil

Author
item Fujinuma, Ryosuke
item Venterea, Rodney - Rod
item ROSEN, C - University Of Minnesota

Submitted to: Journal of Environmental Quality
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 8/12/2011
Publication Date: 11/1/2011
Citation: Fujinuma, R., Venterea, R.T., Rosen, C.J. 2011. Broadcast urea reduces N2O emissions but increases NO emissions compared with conventional and shallow-applied anhydrous ammonia in a coarse-textured soil. Journal of Environmental Quality. 40(6):1806-1815.

Interpretive Summary: Quantifying nitrous oxide (N2O) and nitric oxide (NO) fluxes from corn (Zea Mays L.) production fields under contrasting fertilizer regimes is essential for identifying ways of mitigating agricultural greenhouse gas (GHG) emissions. Corn production consumes approximately 40% of all nitrogen (N) fertilizers applied to agricultural crops in the U.S. and therefore represents a large potential source of GHG emissions.Despite the importance of anhydrous ammonia (AA) and urea as N fertilizer sources in the U.S., there have been relatively few side-by-side comparisons of their effects on GHG emissions, and none have been conducted in coarse-textured or irrigated soils. The objectives of this study were to compare N oxide emissions, grain yield, and N use efficiency (NUE) in a corn production system over two consecutive growing seasons on an irrigated loamy sand in central Minnesota that used three different fertilizer practices: AA that was injected at a conventional depth (AAc) and at a shallower depth (AAs), and urea that was broadcast and incorporated (IU). Different patterns were displayed for N2O and NO emissions: N2O emissions were 40% lower with IU than AAc and were more than twice as high with AAs than AAc, while NO emissions were twice as high with IU as AAc or AAs. Expressed as total N loss (NO + N2O) or as total CO2 equivalents, N oxide emissions increased in the order IU < AAc < AAs. There were no differences in grain yields among fertilizer treatments. However, while the AAs treatment had the greatest GHG emissions, it also used N more efficiently as evidenced by total above-ground crop N yields that were 14% greater than the AAc treatment. Thus, these results provide more evidence that AA can emit more N2O compared with urea, and they also demonstrate that higher NUE may not always correspond with reduced N2O emissions. This information will be useful to corn producers and environmental policy-makers and regulators interested in identifying practices that minimize N2O emissions.

Technical Abstract: Quantifying nitrous oxide (N2O) and nitric oxide (NO) fluxes from corn (Zea Mays L.) production fields under contrasting fertilizer regimes is essential for identifying ways of mitigating agricultural greenhouse gas (GHG) emissions. Despite the importance of anhydrous ammonia (AA) and urea as N fertilizer sources in the U.S., there have been relatively few side-by-side comparisons of their effects on GHG emissions, and none have been conducted in coarse-textured or irrigated soils. In addition, relatively few studies have evaluated agronomic performance together with environmental impacts. The objectives of this study were to compare N oxide emissions, grain yield, and N use efficiency (NUE) in a corn production system over two consecutive growing seasons on an irrigated loamy sand in central Minnesota that used three different fertilizer practices: AA that was injected at a conventional depth (0.20 m) (AAc) and at a shallower depth (0.12 m) (AAs), and urea that was broadcast and incorporated (IU). N oxide emissions were quantified on both an area- and yield-scaled basis, and were also converted to CO2 equivalents after accounting for potential off-site conversion of NO to N2O. Different patterns were displayed for N2O and NO emissions: N2O emissions were 40% lower with IU than AAc and were more than twice as high with AAs than AAc, while NO emissions were twice as high with IU as AAc or AAs. Expressed as total N loss (NO + N2O) or as total CO2 equivalents, N oxide emissions increased in the order IU < AAc < AAs. There were no differences in grain yields among fertilizer treatments. However, while the AAs treatment had the greatest GHG emissions, it also used N more efficiently as evidenced by total above-ground crop N yields that were 14% greater than the AAc treatment. Thus, these results provide more evidence that AA can emit more N2O compared with urea, and they also demonstrate that higher NUE may not always correspond with reduced N2O emissions.