Copper micronutrient fixation kinetics and interactions with soil constituents in semi-arid alkaline soils

This study examined the fixation pattern and kinetics of plant-available [diethylene triamine pentaacetic acid (DTPA)-extractable] copper (Cu), as well as basic soil properties that influence Cu availability in selected semi-arid soils. Soil samples from six different series were used and data obtained from Cu extraction experiments fitted to various kinetic models. Soils were also characterized for a suite of chemical and physical properties. The majority (80%) of the plant-available Cu fixed over the experimental period of 90 d occurred within the first 14 d. The amount of plant-available Cu fixed within the first 14 d tended to be influenced by the combination of organic matter (OM) and pH. The total amount of Cu fixed at the end of the experimental period of 90 d was influenced by pH and a combination of pH and calcium carbonate. The fixation of plant-available Cu over the experimental period was better described by the power function model [R² = 0.90, Standard Error (SE) = 0.099] but poorly by the other models (R²: 0.58 to 0.59), while reactions within the first 35 d were better described by the second-order model (R² = 0.98, SE = 0.008), suggesting a different fixation pattern. Findings from this study provide a basis for a more mechanistic approach to evaluating and comparing the fixation of Cu micronutrient compounds in these semi-arid soils for more scientific management decision making.