Effects of rate and time of potassium application on yield and fiber quality of cotton (Gossyium hirsutum L.) at different fruit positions

Recently, as modern cotton (Gossyium hirsutum L.) varieties including Bt (Bacillus thuringiensis) transgenic cotton are adopted, premature senescence caused by potassium (K) deficiency has become an important problem in cotton production in the Yellow River Valley of China. The objectives of this research were to determine the effects of rate and time of potassium application on cotton yield and fiber quality at different fruit positions. Field studies were conducted in 2009 and 2010 using the cotton cultivar, Lumianyan No. 28. Potassium rates of K2O 0,100 and 150 kg/ha was applied as basal dressing and as 1?2 basal dressing and 1?2 top-dressing at the blossoming and boll forming stages. Data collected in the two years indicate that the application of potassium produces significant differences in seed cotton yield and lint yield compared with the untreated control, respectively. When the K application rate is 150 kg/ha, the split application of K produces significant higher seed cotton yield and lint yield compared with the basal application, respectively. When the fertilizer K is 1/2 basal-applied and 1/2 top-dressed at the blossoming and boll forming stages, seed cotton yield and lint yield are significant increased with increases of the K application rate, respectively, and the influence of K on the number of bolls per plant is the key reason for the increase. The results also show that the micronaire values in middle and upper fruit branches and inner nodes under the K application are significant increased compared with the untreated control. Split application of K2O 150 kg/ha produces significant higher fiber lengths, fiber strength in middle fruit branches and the outer nodes and fiber maturation in middle fruit branches and inner nodes compared with the untreated control, respectively. Moreover, at the same K application time, there were no effects on fiber length and fiber strength with the increase of K application, respectively. At the same K application rate, there was no significant difference in fiber strength between basal application and split application.