Potato (Solanum tuberosum L.) production on sandy soils requires added N. Only 40–60% of the applied N is acquired by the crop. Increased N use efficiency (NUE) and its components, N utilization efficiency (NUtE) and N uptake efficiency (NUpE), could reduce fertilizer rates and environmental losses. We compared N efficiency in fresh-market red potato varieties, in terms of yield and quality traits, and examined potential mechanisms for that efficiency including uptake, utilization, and increased root growth. We grew selections from a red potato breeding population and commercial varieties under two N rates: 101 and 202 kg N ha−1. We compared NUE, NUpE, and NUtE in low and high N. We compared root phenotypes at tuber initiation and yield and skin quality metrics at harvest. Values for NUtE correlated with NUE and yield in low N and NUpE correlated with NUE and yield in high N. Low-N conditions produced smaller tubers, while high N resulted primarily in medium tubers. Nitrogen did not affect skinning and redness but low N did result in slightly lighter skin color. Total root mass 45 d after planting (DAP) correlated with final yield and NUE but did not correlate with measures of N uptake across treatments. Larger roots correlated with NUpE only in the high-N treatment. Selection under low N may reveal NUE and expose more stable representations of the genetic components of skin quality phenotypes. While skinning and skin color were more variable among varieties in low N, within variety they exhibited year-to-year consistency.
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We appreciate Dr. Matthew Clark's thorough comments on the manuscript and Ron Faber's meticulous management of our field sites. Additionally, we'd like to thank the many hands involved in phenotyping this project: Husain Agha, Rachel Figueroa, Katelyn Filbrandt, Jessica Huege, Akpevwe Ikoba, Mitch Johnson, Heather Tuttle, and Alexander Westgaard. Finally, we appreciate the feedback of the editor and three anonymous reviewers. This project was funded by the USDA National Institute of Food and Agriculture award number 2014‐34141‐22487 and 2016‐34141‐25707.
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