Abstract: Taking cotton cultivars Liaomian 19 and NuCoTN 33B as test materials, a field experiment was conducted to study the effects of nitrogen fertilization rate (0, 240 and 480 kg·hm-2) and planting density (75000, 97500 and 120000 plants·hm-2) on the boll biomass and nitrogen accumulation in the extremely early maturing cotton region of Northeast China. With the growth and development of cotton, the biomass and nitrogen accumulation of cotton boll, cotton seed, and cotton fiber varied in ‘S’ shape. Both nitrogen fertilization rate and planting density had significant effects on the dynamic characteristics of boll biomass and nitrogen accumulation, and on the fiber yield and quality. In treatment 240 kg·hm-2 and 97500 plants·hm-2, the biomass of single boll, cotton seed and cotton fiber was the maximum, the starting time and ending time of the rapid accumulation period of the biomass and nitrogen were earlier but the duration of the accumulation was shorter, the rapid accumulation speed of the biomass was the maximum, and the distribution indices of the biomass and nitrogen were the lowest in boll shell but the highest in cotton seed and cotton fiber.

Key words: extremely early maturing cotton region, cotton boll, nitrogen fertilization rate, planting density, biomass, quality