Tillage and Nitrogen Source Effects On Nitrous Oxide Emissions From Irrigated Cropping Systems.

Nitrous oxide emissions were monitored from irrigated corn production systems receiving different N sources at fertilizer rates of 246 kg N/ha when in corn (Zea mays L.), 56 kg N/ha when in dry bean (Phaseolus vulgaris  L.), and 157 kg N/ha when in barley (Hordeum distichon L.).  Cropping systems included: conventional-till continuous corn (CT-CC); no-till continuous corn (NT-CC); NT corn-dry bean (NT-CDb); and NT corn-barley (NT-CB).  In the NT-CC and CT-CC systems, a controlled-release, polymer-coated urea (ESN^®) and dry granular urea were compared.  In the NT-CDb and NT-CB rotations, a stabilized N source (SuperU^®) was compared with urea.  Nitrous oxide fluxes were measured one to three times per week during two growing seasons using static, vented chambers and a gas chromatograph analyzer.  Cumulative growing season N₂O emissions from urea and ESN^® application were not different under CT-CC, but were different under NT-CC, where ESN^® reduced N₂O emissions 49% compared to urea.  SuperU^® reduced N₂O emissions 27% compared to urea with application of 56 kg N/ha to dry bean in 2007 and 54% compared to urea with application of 246 kg N/ha to corn in 2008 in the NT-CDb rotation.  SuperU^® reduced N₂O emissions 19% compared to urea with application of 157 kg N/ha to barley in 2007 and 51% compared to urea with application of 246 kg N/ha to corn in 2008 in the NT-CB rotation.  This work shows that current tillage and fertilizer N technologies that delay release and transformation of N can substantially reduce N₂O emissions from irrigated systems under specific cropping conditions.