Abstract: In order to explore the optimal population structure of mid-early maturing cotton varieties under direct seeding after rape harvest and its supporting chemical control technology, the mid-early maturing cotton varieties were used as test materials, and the split plot design was used to explore the growth and development characteristics of direct seeding cotton after rape harvest and the chemical defoliation and ripening effect of different treatments under high density （60 000,90 000,120 000 and 150 000 plants/hm²） combined with heavy chemical control （spraying 98% DPC360 and 540 g effective components per hectareduring the whole growth period）. The results showed that in the range of experimental density and chemical control, with the increase of density and chemical control, the main stem became thinner, the height of initial fruit branch moved upward, the middle and upper fruit branches shortened, and the dry matter accumulation per plant decreased. The effect of density factor was greater than that of chemical control. Density and chemical control and their interaction had no significant effect on boll number per unit area; with the increase of density, the number of bolls per plant and single boll weight gradually decreased, and the increase of chemical control could reduce lint percentage and increase sub-index. With the increase of density and chemical control, the natural boll opening process of cotton was slow. In each treatment, the yield of cotton with density of 90 000 plants/hm² and DPC360 g/hm² was the highest. Density, chemical control and their interaction had no significant effect on the defoliation effect of cotton sprayed with defoliant ripening agent, had no significant effect on the final boll opening rate, and had more obvious effect on the ripening of small basic boll opening rate. Based on various factors, in Poyang Lake cotton planting area of the Yangtze river basin, the suitable density for direct seeding of mid-early maturing cotton varieties rape after harvest was about 90 000 plants/hm². The chemical control of DPC spraying during the whole growth period should be based on cotton growth and climatic conditions.

Key words: cotton, direct seeding, mid-early maturing varieties, density, chemical control technology