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Nitrogen, Tillage, and Crop Rotation Effects on Nitrous Oxide Emissions from Irrigated Cropping Systems

USDA–ARS, 2150 Centre Ave, Bldg. D, Suite 100, Fort Collins, CO 80526-8119. Contribution from USDA-ARS, Fort Collins, CO. Mention of trade names or proprietary products does not indicate endorsement by USDA and does not imply its approval to the exclusion of other products that may be suitable

^* Corresponding author (ardell.halvorson{at}ars.usda.gov).

Received for publication May 25, 2007. We evaluated the effects of irrigated crop management practices on nitrous oxide (N₂O) emissions from soil. Emissions were monitored from several irrigated cropping systems receiving N fertilizer rates ranging from 0 to 246 kg N ha^–1 during the 2005 and 2006 growing seasons. Cropping systems included conventional-till (CT) continuous corn (Zea mays L.), no-till (NT) continuous corn, NT corn–dry bean (Phaseolus vulgaris L.) (NT-CDb), and NT corn–barley (Hordeum distichon L.) (NT-CB). In 2005, half the N was subsurface band applied as urea-ammonium nitrate (UAN) at planting to all corn plots, with the rest of the N applied surface broadcast as a polymer-coated urea (PCU) in mid-June. The entire N rate was applied as UAN at barley and dry bean planting in the NT-CB and NT-CDb plots in 2005. All plots were in corn in 2006, with PCU being applied at half the N rate at corn emergence and a second N application as dry urea in mid-June followed by irrigation, both banded on the soil surface in the corn row. Nitrous oxide fluxes were measured during the growing season using static, vented chambers (1–3 times wk^–1) and a gas chromatograph analyzer. Linear increases in N₂O emissions were observed with increasing N-fertilizer rate, but emission amounts varied with growing season. Growing season N₂O emissions were greater from the NT-CDb system during the corn phase of the rotation than from the other cropping systems. Crop rotation and N rate had more effect than tillage system on N₂O emissions. Nitrous oxide emissions from N application ranged from 0.30 to 0.75% of N applied. Spikes in N₂O emissions after N fertilizer application were greater with UAN and urea than with PCU fertilizer. The PCU showed potential for reducing N₂O emissions from irrigated cropping systems.

Abbreviations: CT, conventional till • CT-CC, conventional-tillage continuous corn • GWP, global warming potential • N₂O, nitrous oxide • NT, no till • NT-CC, no-till continuous corn • NT-CB, no-till corn–barley • NT-CDb, no-till corn–drybean • NT-CSb, no-till corn–soybean • PCU, polymer-coated urea • SOC, soil organic carbon • UAN, urea ammonium nitrate fertilizer

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