Potassium Timing Application Rates on Cotton Yield, and Leaf Tissues in the Southern Texas High Plains.

Cotton is a major cash crop cultivated mainly for its fiber and seed oil. Cotton is very sensitive to potassium (K) deficiency compared to most other field crops. Potassium is required in photosynthesis, metabolism, osmotic potential maintenance, and water uptake during fiber development. Cotton demands of K range from about 2.2 kg/ha/day to 5 kg/ha/day during boll fill period. A study was conducted in 2016 in Lubbock and Lamesa, TX to determine the effect of K fertilizer rate and application timing on yield and fiber quality of two cotton varieties, DP 1518 B2RF and DP 1612 B2XF. Treatment rates of 0, 90, and 180 kg K ha^-1 applied as pre-plant, side-dress, and split application. Soil and leaf tissues samples were collected at the first bloom stage. Cotton was harvested at the end of the season to determine yield and fiber quality response to K rates. Soil K concentrations at depth (0-15 cm and 15-30 cm) were quantified using three different extractants: Mehlich III (M3), ammonium acetate (AA), and Haney, Haney, Hossner, and Arnold (H3A). Harvest results demonstrated side-dressed K application produced significantly greater lint yields in cotton variety DP 1518 B2RF at both locations in 2016. There was no significant difference between treatments in terms of fiber quality and leaf tissue K. Soil extraction methods demonstrated AA extracting the greatest K concentration (595 mg kg^-1) in Lubbock, whereas Mehlich III resulted in the greatest concentration (470 mg kg^-1) in Lamesa. These preliminary results representing only one year of data were repeated in 2017 to validate the results.