Examining the fixation kinetics of chelated and non-chelated copper and the applications to micronutrient management in semiarid alkaline soils

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 non-chelated system (R²: 0.68–0.94), compared to the chelated (R²: 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 (Cu–Fe), 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 (R² =  0.91, SE  =  0.081) in the non-chelated system and second-order model (R² =  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.