Nitrogen Management Affects Nitrous Oxide Emissions under Varying Cotton Irrigation Systems in the Desert Southwest, USA

Irrigation of food and fiber crops worldwide continues to increase. Nitrogen (N) from fertilizers is a major source of the potent greenhouse gas nitrous oxide (N2O) in irrigated cropping systems. Nitrous oxide emissions data are scarce for crops in the arid western United States. The objective of these studies was to assess the effect of N fertilizer management on N2O emissions from furrow-irrigated, overhead sprinkler-irrigated, and subsurface drip-irrigated cotton (Gossypium hirsutum L.) in Maricopa, AZ, on Trix and Casa Grande sandy clay loam soils. Soil test-and canopy-reflectance-based N fertilizer management were compared. In the furrow-and overhead sprinkler-irrigated fields, we also tested the enhanced efficiency N fertilizer additive Agrotain Plus as a N2O mitigation tool. Nitrogen fertilizer rates as liquid urea ammonium nitrate ranged from 0 to 233 kg N ha(-1). Two applications of N fertilizer were made with furrow irrigation, three applications under overhead sprinkler irrigation, and 24 fertigations with subsurface drip irrigation. Emissions were measured weekly from May through August with 1-L vented chambers. N2O emissions were not agronomically significant, but increased as much as 16-fold following N fertilizer addition compared to zero-N controls. Emission factors ranged from 0.10 to 0.54% of added N fertilizer emitted as N2O-N with furrow irrigation, 0.15 to 1.1% with overhead sprinkler irrigation, and <0.1% with subsurface drip irrigation. The reduction of N2O emissions due to addition of Agrotain Plus to urea ammonium nitrate was inconsistent. This study provides unique data on N2O emissions in arid-land irrigated cotton and illustrates the advantage of subsurface drip irrigation as a low N2O source system.