Improving nitrogen fertilizer use efficiency in subsurface drip-irrigated cotton in the desert southwest

Authors: Bronson, Kevin; Hunsaker, Douglas - Doug; Meisinger, John; Rockholt, Sharette; Thorp, Kelly; Conley, Matthew; Williams, Clinton; NORTON, E - University Of Arizona; BARNES, ED - Cotton, Inc

Submitted to: Soil Science Society of America Journal
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 9/11/2019
Publication Date: 11/27/2019
Publication URL: https://handle.nal.usda.gov/10113/6829301
Citation: Bronson, K.F., Hunsaker, D.J., Meisinger, J.J., Rockholt, S.M., Thorp, K.R., Conley, M.M., Williams, C.F., Norton, E.R., Barnes, E.M. 2019. Improving nitrogen fertilizer use efficiency in subsurface drip-irrigated cotton in the desert southwest. Soil Science Society of America Journal. 83(6):1712-1721. https://doi.org/10.2136/sssaj2019.07.0210.
DOI: https://doi.org/10.2136/sssaj2019.07.0210

Interpretive Summary: Ongoing drought in the American Southwest continues to generate interest in efficient subsurface drip irrigation (SDI). The ability to fertigate liquid urea ammonium nitrate (UAN) at low rates and with high frequency is an important advantage of SDI. However, nitrogen (N) fertilizer management guidelines, specific to SDI cotton are lacking. The objectives of this 3-yr study conducted on a Casa Grande sandy loam soil in Maricopa, AZ, USA were to test a pre-plant soil profile NO3 test algorithm and a canopy reflectance approach to manage in-season N fertilizer for SDI cotton. Treatments included soil test-based N management, reflectance-based N management, and zero-N at 100 % ET irrigation replacement. A second irrigation level of 70 % ET replacement included just the soil test-based N and zero-N treatments. Soil test-based N treatments ranged from 172 to 224 kg N ha-1, and the reflectance-based N amounts were 112 to 158 kg N ha-1. Nitrogen recovery efficiency (RE) of urea ammonium nitrate (UAN)-N was high with 24 fertigations between first square and mid bloom, ranging from 58 to 93%. Residual post-harvest soil NO3-N was notable only with 70% irrigation. Lint and seed yields were significantly reduced with the 70 % irrigation treatment compared to 100% irrigation. On the other hand, lint yields with reflectance-based N management saved 17 to 112 kg N ha-1 without reducing lint yields, compared to the soil test-based N treatment.

Technical Abstract: Declining water availability in the American Southwest continues to generate interest in efficient subsurface drip irrigation (SDI) for cotton (Gossypium hirsutum L.) production. Fertigating urea ammonium nitrate (UAN) at low rates with high frequency is an important advantage of SDI. However, N fertilizer management guidelines, specific to SDI cotton are lacking. A 3-yr study was conducted on a Casa Grande sandy loam soil in Maricopa, AZ, USA to test a pre-plant soil profile NO3 test algorithm and a canopy reflectance approach to manage in-season N fertilizer for SDI cotton. Treatments included soil test-based N management, reflectance-based N management, and zero-N at 100 % ET irrigation replacement. A second irrigation level of 70 % ET replacement included just the soil test-based N and zero-N treatments. The five treatments were replicated three times. Soil test-based N treatments received from 172 to 224 kg N ha-1, and reflectance-based N amounts were 112 to 158 kg N ha-1. Nitrogen recovery efficiency (RE) of UAN-N was high with 24 fertigations during 6 wk between first square and mid bloom, ranging from 58 to 93 %. The isotope dilution method estimated similar RE in 2017. Residual post-harvest soil NO3-N was notable only with 70 % irrigation. Lint and seed yields were significantly reduced with the 70 % irrigation treatment compared to 100 % irrigation. The key result of this study is that reflectance-based N management saved 17 to 112 kg N ha-1 without reducing lint yields, compared to the soil test-based N treatment.