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Abstract: A comprehensive study on the system between the boll development and the climatic conditions for seyeral years show that a preliminary result of the specific heat unit index relative to economic characteristics of the cotton bolls has been obtained. The active accumulated temperature≥15℃ between 1,300—1,500 degree-day is the accumulated temperature index for boll opening under normal conditions. The accumulated temperature for boll opening under normal conditions should be not less than 1,100 degree-day. There is a highly negative correlation between boll setting period and the average daily temperature within the boll setting period with r=-0.9087. The lowest critical temperature for boll opening unclef normal conditions is at 15℃. There is a significant correlation between seed cotton percentage/boll ard the days≥18℃ within the 50 days boll development and the accumulated temperature durirg this period. The lowest critical index for the seed cotton percentage/boll is in 35 days and 800 degree-day. Under the conditions with the average temperature less that 20℃, the percent of matured seeds is no morethan 30％. The fiber quality is closely correlated with the early or late advent of the flowering period and with the water, heat unit and the sunshine. The effective flowering period is Often stopped on August 20 for cottons grown in Anyang. Based on this, it must rely on the bolls set in the mid summer, obtain bolls set in early autumn as many as possible and decrease the percent of autumn bolls in the rank of mid summer bolls, early autumn bolls and autumn bolls as far as possible.

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