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Excessive irrigation can reduce cotton yield, but studies assessing the relative contribution of component physiological processes to yield loss are limited. The objective of the current experiment was to quantify irrigation‐induced yield loss attributable to Intercepted Photosynthetically Active Radiation (IPAR), Radiation Use Efficiency (RUE) and Harvest Index (HI). For three irrigation treatments (well‐watered, over‐irrigated, and dryland) during the 2018 and 2019 growing seasons, biweekly measurements of predawn leaf water potential (ΨPD) and light interception were taken along with measurements of biomass, lint yield, fibre quality and harvest index. Irrigation effects on yield were only observed during the 2019 season, and the results showed that ΨPD remained relatively high in both seasons and was rarely affected by irrigation treatment. A significant reduction in yield was observed for irrigated treatments, despite the dryland producing lower biomass. Any positive effects of IPAR and RUE on lint yield due to excess irrigation were offset by large declines in HI. We conclude that HI was the dominant contributor to yield loss due to excessive irrigation because reduced boll numbers and average boll mass were observed in plots with the greatest total above‐ground biomass.

Cotton (Gossypium hirsutum L.) is not only the dominant fiber crop grown worldwide, but it is also an important source of plant-based oil and protein. Previous research has documented a significant effect of cotton cultivar and nitrogen application individually on lint yield and seed composition, but very limited studies have evaluated the lint, seed, oil, and protein yield responses of cultivars with different seed mass and composition to a broad range of N application rates. The objective of this study was to evaluate the lint, seed, oil, and protein yield responses of cultivars with different seed mass and composition to N application rates (0-168 kg N ha −1 ) for field-grown cotton. A field experiment was conducted in Tifton, GA, USA during the 2019 and 2020 growing seasons that included six cultivars and six N application rates. Cultivar significantly affected seedcotton, lint, seed, and seed reserve yields in both growing seasons. Lint yield did not follow identical trends as seed yield mainly due to cultivar variation in lint percent. Similarly, protein and oil yield were influenced by cultivar variation in seed composition. Seedcotton, seed, protein, and oil yields continually increased with increases in N application from 0 to 168 kg N ha −1 , whereas for lint yield, all fertilized treatments produced comparable yields that were significantly higher (68%) than the 0 kg N ha −1 treatment. We conclude that variability in the distribution of photosynthates to fiber and seed as well as seed oil and protein composition can significantly alter trends in fiber, seed, and seed component yields in response to cultivar or N application rates for field-grown cotton. INTRODUCTIONNitrogen (N) is an essential macronutrient, which is required most consistently and in the highest quantities of any other nutrient for cotton production. Due to the impacts of N availability on cotton growth and physiological response, N deficiency severely limits lint yield in cotton. Snider, Harris