Potassium uptake, utilization, and chemistry in cotton and soils of the Texas Southern High Plains



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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.



Cotton, Potassium, Soil, Lint yield, Pre-plant, Side-dress, Split, Fixation, Mehlich III, Ammonium acetate, H3A, Clay, Texas Southern High Plains