不同脱叶剂对湖南棉区机采棉脱叶效果及产量与品质的影响OA

To investigate the effects of different defoliants and spraying times on defoliation and ripening of cotton(Gossypium hirsutum L.)under different planting densities in Hunan cotton region,a three-location split-plot field experiment was conducted.Spraying time(A)was assigned to the main plots with two levels:spraying at 30%boll opening rate(A1)and spraying at 40%boll opening rate(A2).Planting density(B)was assigned to the subplots with three levels:60 000 plants/hm2(B1),90 000 plants/hm2(B2),and 120 000 plants/hm2(B3).Defoliant type(C)was assigned to the sub-subplots with four levels:Guoguang(50%thidiazuron·ethephon suspension)2 500 mL/hm2(C1),thidiazuron(50%wettable powder)600 g/hm2+ethephon(40%aqueous solution)250 mL/hm2(C2),thidiazuron diuron soluble powder(thidiazuron 50%+diuron 25%)225 g/hm2+ethephon(40%aqueous solution)250 mL/hm2(C3),and a water-sprayed control(CK).The effects of these treatments on defoliation,ripening,yield,and fiber quality of cotton were then evaluated.The results showed that,first,all three defoliants significantly increased the defoliation rate and boll opening rate,with defoliation rate exceeding 90%at 18 days after the treatment.Among them,treatment C1 exhibited the best defoliation performance,with the defoliation rates of 94.83%,95.45%and 98.06%at Changsha,Yueyang,and Hengyang sites,respectively,and also showed the most significant yield increase.Treatment C2 resulted in better fiber upper half mean length,while C1 and C3 were more effective in reducing the micronaire value.Second,spraying time significantly affected defoliation and ripening.Spraying at 40%boll opening rate(A2)resulted in higher defoliation rate,boll opening rate,fiber strength,seed cotton yield and lint yield than spraying at 30%boll opening rate(A1),although the branch retention rate was slightly increased,the overall performance was still better.Third,planting density significantly influenced defoliation and ripening.The medium density treatment(B2,90 000 plants/hm2)showed better defoliation and boll opening performance with a lower branch retention rate compared with low(B1)and high(B3)densities.In terms of yield,B2 and B3 were significantly higher than B1,but both excessively high and low densities(B1,B3)resulted in reduced fiber quality.In conclusion,taking into account the effects of different treatments on defoliation,boll opening,fiber quality,and yield,it is recommended to use a planting density of 90 000 plants/hm2 in the Hunan cotton region,with Guoguang(50%thidiazuron·ethephon suspension)applied when the boll opening rate reaches 40%.