Effect of Nitrogen Rates and Flowering Dates on Fiber Quality of Cotton (Gossypium hirsutum L.)

Nitrogen (N) supply during boll setting and maturation period of cotton can be critical in determining fiber quality. The study aims to investigate the relationship between N rates and formation of fiber length, strength, maturity and micronaire in bolls with different flowering dates. Field experiments were conducted using two cotton cultivars (Kemian 1 and NuCOTN 33B) and three N fertilization rates (0, 240, and 480 kg N ha-1) in Nanjing and Xuzhou in 2005 and in Anyang in 2007, China. The fiber length, strength, maturity, micronaire, and N concentration per unit area (NA) of the subtending leaf of cotton boll were analyzed.
N fertilization rates, flowering dates, and N fertilization rates × flowering dates significantly (P ≤ 0.05) affected NA and the formation of fiber length, strength, maturity and micronaire. N fertilization rates affected fiber quality by influencing NA which was significantly related to rate and duration of the fiber quality formation process. The optimal NA for fiber quality formation was varied. For bolls flowering before August 25, when mean daily temperature during boll maturation period (MDTBMP) was higher than 21°C, NA in the 240 kg N ha-1 treatment was optimal for fiber length, fiber strength, maturity, and micronaire formation. For bolls flowering after September 10 when MDTBMP was lower than 21°C, NA in the 480 kg N ha-1 treatment was optimal for fiber quality development. Higher N application rate can sustain a higher NA level in its subtending leaf, leading to the less decrease magnitude of fiber length, strength, maturity, micronaire in late flowering dates. 240 kg N ha-1 is the recommended N application strategy for optimal quality, but we could diminish the negative influence of climate stress on fiber quality by supplemented N fertilizer in later flowering season.