Cotton reproductive and fiber quality responses to nitrogen nutrition

Nutrient (N) stress affects cotton growth, primary physiological processes andfiber properties. This study utilized two sunlit growth chambers to compare cotton(cv. TM-1) responses to two levels of N nutrition imposed at the onset of floweringstage of development, 100 and 0% of optimum N, in plants grown under otherwiseoptimal temperature and soil moisture conditions. Flowers and bolls were taggeddaily to estimate boll maturation period (BMP). Leaf N concentration wasdetermined every four days from flowering to maturity. Plant height and main stemnodes were determined every four days from emergence to 25 days after treatment(DAT) and photosynthetic measurements were recorded weekly from 0 to 56 DAT.Plant and boll-component dry weights were recorded at end of the experiment.Fiber quality was determined in samples of lint that were grouped based on averageleaf N concentration during the BMP. Total plant biomass was reduced 23% by Ndeficient treatment and these plants produced 14 bolls per plant as compared with21 bolls in N sufficient plants. Stress-induced decrease in leaf N was associatedwith linear decreases in leaf photosynthesis (r2=0.92) and stomatal conductance(r2=0.86). Fiber length and strength increased linearly with increase in lean Nconcentration, while fiber micronaire and uniformity declined linearly withincrease in leaf N concentration. Among the measured fiber properties, fibermicronaire was the most sensitive to changes in leaf N followed by strength, lengthand uniformity. Knowledge of the functional relationship between leaf Nconcentration and a fiber property can be used to develop a fiber quality submodelfor cotton under optimal temperature and water conditions.