Evaluation of Cotton Yield, Quality, and Plant Growth Response to Soil-Applied Potassium

Potassium (K) plays a key role in several critical cotton plant processes, including photosynthesis, activation of protein enzymes, disease and drought stress mitigation, and fiber development. Across the United States Cotton Belt, K deficiency symptoms in cotton have increased over the past decade, which may be reducing lint yield and fiber quality in these areas. In 2015 a project was initiated at 12 locations across the Cotton Belt with the objectives of: 1) quantifying soil K concentrations (at depth) from major cotton production regions in the Cotton Belt experiencing K deficiencies; and 2) evaluating the impact of K application methods and rates on cotton lint yield, quality, and economic return on investment (ROI). Based on these results, the goal was to re-evaluate soil K recommendations and modify as appropriate to optimize yields. Both granular (0-0-60) and liquid (0-0-15) muriate of potash (KCl) sources of K were applied two to four weeks prior to planting cotton at rates of 0, 40, 80, 120, and 160 lb/A K₂O. In 2016, trial locations were divided, with nine being designated as new sites meaning that a new field location was selected each year of the study (Alabama, Arkansas, Louisiana, Mississippi, North Carolina, Oklahoma, Texas - Lubbock and Williamson Counties, and Virginia).

Discussion of results will include soil macronutrient concentrations at depths of 0 to 6”, 6 to 12”, and 12 to 24” and cotton lint yield. Locations other than Texas and Oklahoma generally had soil K concentrations less than 150 mg/kg (critical level of K, Mehlich 3), and as such, a yield response to applied K fertilizer was expected. In 2015 and 2016, a significant treatment effect was determined at three locations. Two of those, Williamson County, Texas, and Virginia, had lower yields than most other locations. A positive lint yield response to knife-injected K fertilizer (0-0-15) was measured in 2015 at the Lubbock County location. Inconsistent yield responses at locations with limited soil K or with soil K concentrations well above the critical level indicate that K dynamics in cotton are not well understood and deserve continued investigation.