Cotton physiological and agronomic response to nitrogen application rate

Abstract Recently published information on cotton agronomic and photosynthetic component responses to nitrogen (N) application rate is limited for the southeastern US. This experiment was conducted to 1) evaluate cotton yield, fiber quality, growth, and maturity responses to N application rate and 2) quantify associations between photosynthetic component processes and N-induced variation in net photosynthesis. A two-year field experiment was conducted during the 2015 and 2016 growing seasons at a field site in Tifton, GA and evaluated cotton agronomic and physiological response to six N fertilizer application rates ranging from 0 to 168 kg N ha−1. Cotton lint yield was 42–51% lower in 0 N treatments than all other fertilized treatments in both years of the study, and N rates that substantially limited yield decreased final plant height, reduced mainstem node development, and substantially hastened maturity. Date of cutout ranged from 73 to 91 DAP for all N rates and years of the study. Photosynthetic rates were also responsive to N rate on later sample dates (July and August) for both growing seasons. Although declines in chlorophyll content, specific leaf nitrogen, and stomatal conductance were observed for low N plants in some instances, none of these parameters were strongly associated with net photosynthesis overall. In contrast, light-dependent electron transport rate (ETR) was strongly correlated with N-induced variation in net photosynthesis. Estimates of ETR may need to be included along with SLN estimates in future efforts to scale from leaf to canopy level photosynthetic performance in cotton.