Optimal internal nitrogen use efficiency for irrigated cotton in the Southwestern United States

Authors: Bronson, Kevin

Submitted to: Agronomy Journal
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 3/17/2021
Publication Date: 5/14/2021
Citation: Bronson, K.F. 2021. Optimal internal nitrogen use efficiency for irrigated cotton in the Southwestern United States. Agronomy Journal. 113(3):2821-2831. https://doi.org/10.1002/agj2.20674.
DOI: https://doi.org/10.1002/agj2.20674

Interpretive Summary: Nitrogen is the most important nutrient in the production of field crops like cotton. Field studies on N use efficiency usually focus on recovery efficiency of added N fertilizer or agronomic N use efficiency, the increase in yield with added N. The internal N use efficiency of N (iNUE) or lint yield divided by plant N uptake is less studied, but is a key component of N fertilizer recommendations. The objective of this study was to identify the optimum iNUE for irrigated cotton in West Texas and Arizona. Eighteen site-years of data from N fertilizer management studies from Lubbock, TX and Maricopa, AZ from 2000 to 2018 were employed in the study. Total N uptake was determined at first open boll, before leaf senescence commenced. Average lint yields were 1490 kg ha¬-1 for W. Texas (elevation 1000 m) and 1600 kg ha-1 for the warmer, long cotton seasons of Arizona (elevation 360 m). Total N uptake for N-fertilized plots was 128 and 177 kg N ha-1 for W. Texas and Arizona, respectively, reflecting N rates of 91 and 133 kg N ha-1. Average iNUE across both sites was 11.8 kg lint kg plant N-1, which is close to the optimum iNUE of 12.3 ± 0.5 kg lint kg plant N-1, which we estimated by a model of lint yields vs. total N uptake. The optimum iNUE corresponded to an 1800 kg lint ha-1 yield and a 146 (± 5) kg N ha-1 uptake in the plant. Nitrogen uptake by cotton plants greater this was theoretically luxury uptake. Updated data on optimum iNUE can feed directly into improving current N fertilizer recommendations based on pre-plant soil NO3 tests. In turn, this will translate to greater profits for cotton producers in the Southwestern USA and reduction in export of N from the soil, resulting in protection of groundwater from NO3 leaching and reduction in emissions of the greenhouse gas N2O.

Technical Abstract: Nitrogen is the most important nutrient in the production of cotton (Gossypium hirsutum L.). Field studies on N use efficiency usually focus on recovery efficiency of added N fertilizer or agronomic N use efficiency. The internal N use efficiency of N (iNUE; lint yield divided by plant N uptake) is less studied but is a key component of N fertilizer recommendations. The objective of this study was to identify the optimum iNUE for irrigated cotton in West Texas and Arizona. Eighteen site-years of data from N fertilizer management studies from Lubbock, TX and Maricopa, AZ from 2000 to 2018 were used. Lint yields with N-fertilized plots averaged 1535 and 1790 kg ha-1 for West Texas and AZ, respectively. Corresponding N uptake averaged 128 and 177 kg N ha-1 for W. Texas and Arizona, reflecting average N fertilizer rates of 91 and 133 kg N ha-1. An optimum iNUE of 12.3 ± 0.5 kg lint kg plant N-1 was estimated by a linear-plateau model of lint yields vs. total N uptake. Optimum iNUE corresponded to 1800 kg lint ha-1 yield and 146 (± 5) kg N ha-1 plant uptake. Nitrogen uptake by cotton plants greater than this was theoretically luxury uptake. Updated data on optimum iNUE can feed directly into improving current N fertilizer recommendations based on pre-plant soil NO3 tests. In turn, this can translate to greater profits for cotton producers in the Southwestern USA and the reduction in export of N from irrigated cotton fields.