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Cotton (Gossypium hirsutum L.) and potassium (K) dynamics are not well understood particularly in soil with high K levels (>125 mg K kg-1). Reports suggest modern cotton cultivars demand greater K due to their increased yield and faster fruiting tendencies. A major consideration in applying K fertilizer for cotton production is pre-plant soil testing results. Two common methods used to determine K in soil are the Mehlich III (M3) and ammonium acetate (NH4OAc) procedures. These extractants are both ammonium-based which leads to the question of whether these methods may be over-estimating K due to the exchange relationship between K and ammonium (NH4+) in soil with 2:1 clays (illite, smectite, vermiculite) and potential K fixation. Studies were conducted in 2016 and 2017 in Lubbock (Olton clay loam and Acuff loam) and Lamesa (Amarillo fine sandy loam), TX, to (1) determine the effects of K application rate (0, 90, and 180 kg K ha-1) and timing (pre-plant [PP], side-dress [SD], or split applications [split, 40% PP and 60% SD] on lint yield and fiber quality of modern cotton cultivars (DP 1518 B2XF, DP 1522 B2XF, DP 1321 B2XF and DP 1612 B2XF), (2) compare the amount of extractable K determined by M3, NH4OAc and a non-ammonium based extractants, the Haney method (H3A) as a percentage of the total exchangeable K (sodium tetraphenylborate-K), and (3) determine K fixation potential of these soils and the fixation relationship with soil texture and mineralogy. Cotton harvest results determined that pre-plant and side-dress K applications produced significantly greater lint yield with DP 1518 B2XF at both locations, while effects on fiber quality varied by location and years. The response of DP 1518 B2XF to K fertilizer was likely due to greater K use efficiency and K demand of this cultivar compared to the others. Potassium extraction results determined greater K extracted by M3 and NH4OAc than H3A in pre-plant soil samples possibly due to the absence of NH4+ in H3A. Fixation results determined potential fixation of 30 - 60 % of added K across locations. X-ray diffraction analysis at each location determined both soils contained illite, possibly the main source of K, with illite-smectite conversions controlling K release into the soil solution. To better understand soil and cotton K dynamics, research across the United States Cotton Belt is needed to validate the method of soil testing (based on soil mineralogy), effect of application timing, demand of K in cotton and the effects on lint yield and fiber quality of modern cotton cultivars.

When comparing soil potassium (K) levels common in west Texas to the current Mehlich III-K critical level for cotton (Gossypium hirsutum L.), applications of fertilizer K are not often recommended. However, when K is applied to soil, positive responses in yield of cotton have been reported. The objectives of this research were to: 1) Evaluate the effect of different application methods and rates of K fertilizer on cotton growth, lint yield, and fiber quality; 2) Evaluate the effect of K fertilization on lint yield and fiber quality components within specific node zones; and, 3) Determine the effect of K fertilizer rates within irrigation levels on lint yield and boll distribution. In Lamesa muriate of potash (KCl) was applied using two methods, knife injected (0-0-15) and broadcast (0-0-60), and at New Deal KCl was applied using the knife injected method. Rates of K application included 0, 45, 90, 135, and 180 kg ha-1 with high and low irrigation levels. At Lamesa in 2016 lint yield was greater when 90 kg K ha-1 was applied broadcast under high irrigation (2,153 kg ha-1 lint) compared to the 180 kg ha-1 treatment under high irrigation and all K treatments under low irrigation. There were no differences in 2017 for yield at Lamesa. It can be concluded from this experiment that K rates affected bulk lint yield when applied by broadcasting compared to the injection application method in 2016 at the Lamesa, TX, location. At New Deal lint yield differences were not identified for K application rate, while a difference in irrigation was observed, where the high irrigation level increased machine harvested yield on average by 940 kg ha-1 in 2016 and 425 kg ha-1 in 2017. Similar to previous research, irrigation had an effect on boll distribution. At New Deal total bolls in 2016 under the low irrigation resulted in an 175,000 boll ha-1 increase at 135 kg K ha-1 over 45 and 90 kg K ha-1. Differences did not exist in 2016 for box picking yield between K treatments in New Deal. When 180 kg K ha-1 was applied total bolls and box picking yield under low irrigation increased in the early and middle node zones and total nodes over all other K application rates at New Deal in 2017. Based on box picking results from 2017, 180 kg K ha-1 significantly increased yield under the low irrigation in New Deal. In 2016, 135 kg K ha-1 and in 2017, 180 kg K ha-1 tended to have more bolls in the early node zone under the low irrigation and the middle node zone across both irrigation levels. Box picking helped determine that the early and middle node zones were able to utilize the K within the plant due to the increase in bolls and yield compared to the late and vegetative node zones. Our results in the overall bulk lint yield suggest further research is needed to better understand the dynamics of K and cotton production and the effects on lint yield between irrigation levels and application methods.

The quality of water used as the spray carrier, tank-mix combinations, weed size at application, and appropriate tank cleanout procedures are four factors among many others that will impact the success of auxin-based weed control systems in cotton. Multiple trials were conducted near Lubbock, TX from 2012 to 2015 to evaluate these factors. In water quality studies, water source affected glyphosate control in three of six trials when evaluated 21 days after treatment. As expected, an increase in glyphosate rate increased weed control for all six trials. The addition of ammonium sulfate, a water conditioner, also increased weed control for all six trials. When considering weed management systems, numerous effective systems were identified; however, systems containing Enlist Duo® or 2,4-D choline early postemergence and mid-postemergence were among the most effective. These systems provided 85 to 97% control while systems that relied on glufosinate alone mid-postemergence only achieved 28 to 66% control. When evaluating Palmer amaranth, Russian-thistle, and kochia control in non-crop, single postemergence application studies, treatments that consisted of Enlist Duo® or 2,4-D choline alone or as part of a tank-mix combination were the most successful. The greatest level of weed control for all three weed species was achieved at the 3 to 5 cm timing; however, weed size was most critical for Palmer amaranth and Russian-thistle when compared to kochia. When examining spray drift and tank contamination of Enlist Duo® on non-tolerant cotton in the Texas High Plains, nine leaf cotton was more sensitive than cotton at first bloom. This research suggests that non-2,4-D tolerant cotton is extremely sensitive to 2,4-D injury and that predicting yield loss based on visual injury is unreliable. In order to minimize the risk of drift while using these new technologies, applicators must use appropriate spray nozzle and pressure combinations, tank-mix only with permissible partners, apply only when temperature, relative humidity, wind speed, and wind direction are suitable, and respect buffer zone requirements and sensitive habitats. Critical application requirements will be outlined on herbicide labels and industry websites.