Nitrogen Deficiency Alters Cotton Reproductive Performance and Fiber Quality.

Nitrogen stress in upland cotton is one of the most important abiotic stress factors that affect cotton growth, yield and fiber properties. Quantitative relationships between nitrogen and cotton growth, yield, and fiber quality parameters are needed to improve predictive capability of cotton models.  An experiment was conducted by imposing two nitrogen treatments (0 and 100% of recommended N) on cultivar TM-1 grown under optimum water and temperature conditions. Pigments, gas exchange processes and physiological measurements were recorded on topmost fully-expanded leaves. Flowers and open bolls were tagged daily to estimate boll maturation period. Growth, biomass, boll components and fiber quality parameters were measured at the end of the experiment. The plant nitrogen status was monitored by collecting leaf samples twice weekly. Plant biomass was greater at optimum N level (241 g/plant) and declined by 23% (184 g/plant) at low nitrogen level treatment. Individual boll weights were greater at optimum nitrogen concentration and declined under N deficiency. Leaf chlorophyll content substantially declined in the nitrogen deficient plants. Maximum leaf photosynthesis (31.07 µmole CO₂ m^-2 s^-1) were observed at optimum N level, and declined about (24.12 µmole CO₂ m^-2 s^-1) in N deficient treatment due to significant decline in leaf pigment concentration. Although nitrogen deficiency did not consistently increase fiber uniformity, but fiber length and strength declined with nitrogen stress. However, fiber micronaire consistently increase with nitrogen deficiency. The functional relationships between nitrogen concentration and boll growth and fiber properties will be useful to develop fiber models under optimal water and temperature conditions.