Effects of sowing date and density on population characteristics of super short-season insect-resistant cotton

Using the super short-season insect-resistant cotton 546 as materials,the population characteristics were researched under the treatments of different sowing dates(sowing dateⅠ: May 20;sowing dateⅡ: June 2;sowing date Ⅲ: June 14) and sowing densities(low density: 12×104 plants/hm2;middle density: 15×104 plants/hm2;high density: 18×104 plants/hm2) in central Hebei areas.The results were as follows:(1) The fruit branch number per unit area reduced obviously with the delay of sowing date and the decrease of planting density.Effective fruit-branches of threedensities under the treatment of sowing date Ⅲ were equivalent to one third to one half of that under sowing dateⅠ treatment.(2) As the sowing date delayed,the number of flowers per unit area decreased obviously at all growing stages,especially for the treatment of sowing date Ⅲ.(3) The number of effective bolls per unit area at boll opening stage was not significantly different among the three densities of sowing dateⅠ,and it was the highest under the middle density of sowing date Ⅱ,and under the high density of sowing date Ⅲ,respectively.(4) The adverse effect on dry matter accumulation for late sowing had been weakened effectively by increasing the density properly.However,the population nutrient accumulation of sowing date Ⅲ lagged dramatically behind the others'.(5) The dry matter accumulation of reproductive organs per unit area was mainly influenced by different sowing dates and densities.And for the treatment of sowing date Ⅲ,the dry matter accumulation of population reproductive organs during the flowering and fruiting stage was lower greatly than those of sowing date Ⅰand Ⅱ.(6) The dynamics of leaf area index(LAI) of all sowing dates generally showed the order of highmiddlelow density.Since full-boll stage,however,the differences among the three densities were not significant,and after full-bloom stage the LAI of sowing date Ⅲ was reduced more quickly than the others'.The results have provided a basis for the demonstration and growth regulation of this type variety(strain).