Nitrogen management impacts nitrous oxide emissions under varying cotton irrigation systems in the American Desert Southwest

Authors: Bronson, Kevin; Hunsaker, Douglas - Doug; Williams, Clinton; Thorp, Kelly; Rockholt, Sharette; Del Grosso, Stephen - Steve; Venterea, Rodney - Rod; Barnes, Edward

Submitted to: Journal of Environmental Quality
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 12/11/2017
Publication Date: 1/12/2018
Citation: Bronson, K.F., Hunsaker, D.J., Williams, C.F., Thorp, K.R., Rockholt, S.M., Del Grosso, S.J., Venterea, R.T., Barnes, E.M. 2018. Nitrogen management impacts nitrous oxide emissions under varying cotton irrigation systems in the American Desert Southwest. Journal of Environmental Quality. 47:70-78.

Interpretive Summary: Nitrogen from fertilizer use in agriculture is a major source of the potent greenhouse gas nitrous oxide (N2O). However, N2O emission data is lacking for row crops in the Western USA, especially, the desert southwest. The objective of these studies was to assess the effect of N fertilizer management on N2O emissions from furrow- (FI), overhead sprinkler- (OSI), and subsurface drip-irrigated (SDI) cotton (Gossypium hirsutum L.) in Central Arizona. We also tested the enhanced efficiency N fertilizer, Agrotain Plus for the FI and OSI fields as an N2O mitigation management option. Cotton was planted from mid-April to May 1 from 2012 to 2017 on 1-m-wide raised beds. Nitrogen fertilizer as liquid urea ammonium nitrate (UAN) (32-0-0) was applied at rates of 0 to 233 kg N ha-1. Emissions of N2O were measured weekly with 1-Li chambers placed for 24-minute periods from May to August. Nitrous oxide emissions were not agronomically significant, but increased as much as 16-fold, compared to zero-N, with the addition of N fertilizer. Emission factors, (percent of added N fertilizer emitted as N2O-N), ranged from 0.10 to 0.54 % with FI, 0.15 to 1.1% with OSI, and < 0.1 % with SDI. The addition of Agrotain Plus to UAN had little effect on N2O emissions. Nitrous oxide emissions SDI were very low, similar to fluxes from zero-N plots in the FI and OSI fields.

Technical Abstract: 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 US. The objective of these studies was to assess the effect of N fertilizer management on N2O emissions from furrow- (FI), overhead sprinkler- (OSI), and subsurface drip-irrigated (SDI) 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 FI and OSI 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 (UAN) ranged from 0 to 233 kg N ha-1. Two applications of N fertilizer were made with FI, three applications under OSI, and 24 fertigations with SDI. 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 FI, 0.15 to 1.1% with OSI, and < 0.1% with SDI. The reduction of N2O emissions due to addition of Agrotain Plus to UAN was inconsistent. This study provides unique data on N2O emissions in arid-land irrigated cotton and illustrates the advantage of SDI as a low N2O source system.