Quantifying physiological contributions to nitrogen-induced yield variation in field-grown cotton

Context or problem: The effect of nitrogen (N) application rate on lint yield and yield components have been studied extensively in cotton. However, reports quantifying contributions to N-induced yield loss and the response of intra-boll yield components to N deficiency are far less common. Objectives: The objectives of this study were to 1) determine the effect of N application rate on lint yield biomass and fiber quality in cotton, 2) assess the contributions of intercepted photosynthetically active radiation (IPAR), radiation use efficiency (RUE), and harvest index (HI) to N-induced yield loss in cotton, and 3) characterize the effect of N application rate on yield component responses in cotton. Methods: An experiment was conducted at a field site near Tifton, Georgia, USA during the 2021 and 2022 growing seasons. The experiment was arranged as a randomized complete block design with five replications and five nitrogen application rates (0, 44, 89, 134, and 179 kg N ha -1). The studied parameters were lint yield, IPAR, RUE, HI, fiber quality, yield components, and yield loss contributions. Results: Lint yield was significantly affected by N application rate, with yields ranging from 1452 to 1848 kg ha -1. Similarly, total IPAR was 23% lower for the 0 kg N ha- 1 treatment than the 134 kg N ha- 1 treatment, and IPAR contributed significantly to yield loss, with a 427 kg ha- 1 loss attributable to IPAR under N deficiency. RUE was 37% higher for the 179 kg N ha- 1 treatment than the 0 kg N ha- 1 treatment and contributed positively to yield in the highest N rates (179 kg N ha -1). However, yield improvements due to RUE were mitigated by low HI values in the highest N application rate. Boll density was the most strongly and positively associated yield component parameter with N-induced variability in lint yield, whereas lint percent and lint production per seed were negatively associated with lint yield. Conclusions: Among the three physiological yield-driving parameters, light interception by the canopy was the primary contributor to N-induced yield loss. Boll density was the primary yield component governing N-induced variation in lint yield. Increased N application rate promotes greater dry matter partitioning to seeds than fiber, resulting in more seeds per boll and lower lint percent, lint weight per seed, and individual fiber weight. Implications or significance: The results contained here identify the most important functional traits for deter-mining lint yield response to N application rate.