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Abstract. This study examined and compared the fixation and fixation kinetics of copper (Cu) in chelated (ethylene diamine tetraacetic acid, EDTA) and non-chelated mixed systems of micronutrients in the semiarid soils of the Southern High Plains, USA, using findings from Cu extraction studies and kinetic models. Approximately, 22 % more Cu was fixed in the non-chelated system compared to the chelated within the first 14 days with only 7 % difference between the two systems by day 90. Findings suggest a decrease in the effectiveness of chelated micronutrients over time, highlighting the significance of timing even when chelated micronutrients are used. The strengths of the relationship of change in available Cu with respect to other micronutrients (iron (Fe), manganese (Mn), and zinc (Zn)) were higher in the nonchelated system (R 2 : 0.68-0.94), compared to the chelated (R 2 : 0.42-0.81), with slopes of 0.40 (Cu-Fe), 0.31 (Cu-Mn), and 1.04 (Cu-Zn) in the non-chelated system and 0.26 (CuFe), 0.22 (Cu-Mn), and 0.90 (Cu-Zn) in the chelated system. Reduction in the amount of available Cu was best described by the power function model (R 2 = 0.91, SE = 0.081) in the non-chelated system and second-order model (R 2 = 0.95, SE = 0.010) in the chelated system. The applications generated from this study could be used as tools for improved micronutrient management and also provide baseline data for future work in other semiarid/arid alkaline soils of the world. Findings are also more applicable to field settings, an improvement over related previous studies.

Cotton (Gossypium hirsutum L.) and potassium (K) dynamics are not well understood particularly in soils with high K levels. Potassium is important for cotton reproductive development as it influences the number, size and weight of bolls and can improve fiber THIS ARTICLE IS PROTECTED BY COPYRIGHT. ALL RIGHTS RESERVED. 2 quality, by mitigating moisture stress. In the case that soil cannot replenish solution K from exchangeable reserves to meet the plant demands, deficiencies may occur leading to decreased yield (lint and seed) and fiber quality, reduced drought and disease tolerance, and premature boll opening. Studies were conducted in 2016 and 2017 in Lubbock (Olton clay loam and Acuff loam) and Lamesa (Amarillo fine sandy loam), TX, to determine the effects of K application rates and timing on lint yield and fiber quality of modern cotton cultivars (DP 1518 B2XF, DP 1522 B2XF, DP 1321 B2XF and DP 1612 B2XF). Pre-plant soil tests were greater than 250 mg kg -1 at both locations and years at the 0 -15 cm soil depths. Potassium treatments were applied at 0 (control), 90, and 180 kg K ha -1 as pre-plant, sidedress, or split applications. Harvest results determined that pre-plant and side-dress K applications produced significantly greater lint yield only for DP 1518 B2XF at both locations, while effects on fiber quality varied by location. The response of DP 1518 B2XF to K fertilizer was due to greater K use efficiency and possibly K demand of this cultivar compared to the others. This research provides evidence for continued investigation of cultivar by environment-based K management.

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