Cotton reproductive and fiber quality responses to nitrogen nutrition

Nutrient (N) stress affects cotton growth, primary physiological processes and fiber 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 flowering stage of development, 100 and 0% of optimum N, in plants grown under otherwise optimal temperature and soil moisture conditions. Flowers and bolls were tagged daily to estimate boll maturation period (BMP). Leaf N concentration was determined every four days from flowering to maturity. Plant height and main stem nodes 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 average leaf N concentration during the BMP. Total plant biomass was reduced 23% by N deficient treatment and these plants produced 14 bolls per plant as compared with 21 bolls in N sufficient plants. Stress-induced decrease in leaf N was associated with linear decreases in leaf photosynthesis (r2=0.92) and stomatal conductance (r2=0.86). Fiber length and strength increased linearly with increase in lean N concentration, while fiber micronaire and uniformity declined linearly with increase in leaf N concentration. Among the measured fiber properties, fiber micronaire was the most sensitive to changes in leaf N followed by strength, length and uniformity. Knowledge of the functional relationship between leaf N concentration and a fiber property can be used to develop a fiber quality submodel for cotton under optimal temperature and water conditions.