Effects of Planting Densities on the Growth and Distribution of Root in Cotton(Gossypium hirsutum L.)

In this study,the properties of root growth and distribution in cotton regulated by planting densities have been investigated based on the soil core sampling method.At the density of 1.5×104～8.7×104 plants·hm-2,the root dry weight density and the root length density were both gradually increased before the beginning of boll opening stage,then decreased along with the growth progression.However,the above root traits reached the highest at the peak bolling stage at the density of 10.5×104 plants·hm-2,being much earlier than the low planting densities.From the budding peak stage to the early-flowering stage,the root dry weight densities and the root length densities in cotton all showed a pattern to be elevated along with the increase of planting densities.During the growth phase from the full-blooming stage to the beginning of boll opening stage,the root dry weight density was the highest at 3.3×104 plants·hm-2 among the tested planting densities.The root length densities at 3.3×104 to 10.5×104 plants·hm-2 was significantly higher than that at 1.5×104 plants·hm-2.Root vertical distribution analysis revealed that the root dry weight and root length in top soil layer(0～30 cm) accounted for 67.80%～97.44% of the total root weight,and 54.01%～93.33% of total root length(0～60 cm soil layer),respectively.At lower planting densities(1.5×104 plants·hm-2 and 3.3×104 plants·hm-2),the root dry weight densities and root length densities in top soil layer(0～20 cm) were lower than other high planting densities at the budding peak stage.Similarly,the low planting densities mentioned previously had lower above root traits than the high planting densities in deep soil layer(30～60 cm) at growth phase from the early-flowering stage to the peak bolling stage.It did not display a significant variation on root length densities among the tested planting densities in deep soil layer at the beginning of boll opening stage.