Effect of Potassium Management on Lint Yield and Fibre Quality of Cotton in North China

Thirty cotton fields were randomly selected in Hebei, Henan, Shandong, and Xinjiang province to investigate the relationship between soil K supply and cotton yield/fiber quality. The effects of rate and time of K application on cotton yield and fiber quality were also studied in each province. The average soil exchangeable K values of selected cotton fields were higher in Xinjiang (244 mg/kg) and Shandong (267 mg/kg) than in Hebei (107 mg/kg) and Henan (126 mg/kg). Similarly, K supply values of cotton fields (represented by K uptake) were higher in Shandong and Xinjiang provinces than in Hebei and Henan provinces.

A major portion (50 to 64%) of plant K was accumulated in later stages of cotton growth (i.e. after flowering). This suggested that adequate soil K supply in the later stages of plant growth was important for cotton. There were quadratic polynomial relationships between soil exchangeable K and seed cotton (R²=0.26) and between soil exchangeable K and lint yield (R²=0.23). Fiber elongation, fibre strength, and spinning coefficient were positively correlated to soil exchangeable K. However, when soil exchangeable K was above 393 mg/kg, the quality of fiber decreased. Fiber length uniformity increased with the increase in K uptake. Total K uptake of cotton plants was positively related with fibre strength (R²=0.15), fibre elongation (R²=0.51), and spinning coefficient (R²=0.35), and quadratic equations described these relationships better. Based on the one-year experimental data in 2012, the recommended K rates for cotton in Hebei, Henan, Shandong, and Xinjiang were calculated as 150, 120, 180, and 112 kg K₂O/ha, respectively, and the suitable time for K application time was found to be 50% applied at bud stage and 50% applied at boll stage. NWC Cotton K