Abstract:

【Objective】 To investigate the relationship between nitrogen concentration in the subtending leaf of cotton boll and fiber quality indices, and to provide theoretical basis for monitoring nitrogen status in fiber quality formation of bolls with different anthesis dates. 【Method】 Field experiments were carried out in Nanjing (118o50′E, 32o02′N) and Xuzhou (117°11′E, 34°15′N), representing different ecological conditions in the middle lower reaches of Yangtze River Valley and the Yellow River Valley in China. Two cotton cultivars and three nitrogen application levels were applied. The three N levels were 0, 240 and 480 kgN?ha-1, representing low, medium and high nitrogen level, respectively, and the two cultivars were KC-1 and AC-33B with different fiber quality indices. Responses of LMA (leaf mass per unit leaf area) and nitrogen concentration (NM, nitrogen content per unit leaf mass; NA, nitrogen content per unit leaf area) in the subtending leaf of cotton boll to nitrogen application levels were studied, and the relationships between nitrogen concentration and fiber quality indices were firstly groped. 【Result】 (1) NA in the subtending leaf of cotton boll contained both the information of LMA and NM, possessed the special sensitive characteristic in response to nitrogen application levels and anthesis dates. It can reflect the increasing trends with anthesis date postponing and significant difference in nitrogen treatments. (2) With the average values of NA increasing, the changing trends of pivotal quality indices (length, strength, micronaire and uniformity) of cotton fiber according with the curve of parabola with peak value. (3) With anthesis date, postponing, the difference of NA between low-nitrogen and medium-nitrogen treatments enlarged gradually, on the contrary, the difference between high-nitrogen and medium-nitrogen treatments diminished gradually, fiber strength and micronaire also showed similar trends between corresponding nitrogen treatments. 【Conclusion】 NA in the subtending leaf of cotton boll is tightly related to fiber quality indices formation. As the corresponding relationships between NA and fiber indices are not affected by cotton varieties and ecological sites, it is proposed that NA in the subtending leaf of cotton boll could be used as a practical physiologic index for timely monitoring nitrogen status for fiber quality in the future.

Key words: Gossypium hirsutum L., subtending leaf of cotton boll, leaf nitrogen concentration, anthesis date, nitrogen level, fiber quality