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 (N 2 O) 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 N 2 O 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 N 2 O 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. N 2 O 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 N 2 O‐N with furrow irrigation, 0.15 to 1.1% with overhead sprinkler irrigation, and <0.1% with subsurface drip irrigation. The reduction of N 2 O emissions due to addition of Agrotain Plus to urea ammonium nitrate was inconsistent. This study provides unique data on N 2 O emissions in arid‐land irrigated cotton and illustrates the advantage of subsurface drip irrigation as a low N 2 O source system. Core Ideas N 2 O emissions under overhead sprinkler and furrow irrigation were 0.5 to 1 %. Subsurface drip irrigation combined with 24 fertigation events had an emission factor of 0–0.1 %. The use of enhanced efficiency fertilizers NBPT and DCD had inconsistent mitigation effects on N 2 O emissions. Reduction in N 2 O emissions with canopy reflectance‐based N management was inconsistent.