Chemical Detopping Increases the Optimum Plant Density in Cotton(Gossypium hirsutum L.)

Field experiments were conducted in Akesu city(41°17′N,86°26′E) in Xinjiang cotton planting area from 2009 to 2010 to determine the effect of chemical detopping(i.e.applying the mixture of mepiquat chloride and inorganic salt to retard the growth of main stem strongly) on the optimum density of cotton,with hybrid Zhaofeng1 as material and manual detopping as control.The results indicated that the averaged plant height increased by 17% in chemical detopping compared to control across 180 000,225 000 and 270 000 plants·hm-2.The length of middle and upper sympodials of chemical detopping treatment decreased by 10% and 75%,respectively,and the light transmittance at middle canopy was enhanced about 13%.At the same density,the number of sympodials and nodes of main stem per hectare for chemical detopping treatment was greater than that of control.The lint yield of chemical detopping was 2541 kg·hm-2 at density of 180 000 plants·hm-2,similar to that of control.When plant density increased to 225 000 plants·hm-2,the lint yield of chemical detopping increased slightly but not significantly(2600 kg·hm-2),whereas the yield of control decreased by 10% significantly.Therefore,the optimum density of cotton was extended by chemical detopping,which probably raise cotton yield by increasing boll numbers in Xinjiang area.Chemical detopping did not impact cotton fiber quality.