Nitrous Oxide Emissions from Irrigated Cropping Systems

We evaluated the eff ects 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.) (NTCDb), 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. Th e 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 midJune followed by irrigation, both banded on the soil surface in the corn row. Nitrous oxide fl uxes 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 eff ect 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. Th e PCU showed potential for reducing N2O emissions from irrigated cropping systems. Nitrogen, Tillage, and Crop Rotation Eff ects on Nitrous Oxide Emissions from Irrigated Cropping Systems