Availability and fixation kinetics of added micronutrients in semi-arid alkaline soils of the southern high plains



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The relationship between the deficiency of a nutrient in plants and its concentration in the soil is complex and influenced by numerous factors such as climatic and soil conditions. Soils of arid to semi-arid regions like the Southern High Plains (SHP) of the US are often characterized by soil conditions that can favor the fixation of micronutrients, for instance, alkaline soil pH conditions and high contents of calcium carbonates. Such factors influencing the chemistry and availability of micronutrient not only vary greatly across regions, but also, based on the heterogeneous nature of soil, could differ even on the smallest scale. The lack of site-specific information and the limitations identified in previous studies, such as restrictions to short-term investigations, prompted a suite of studies on the chemistry of micronutrients on semi-arid soils of the SHP. Hence, this study aimed to examine the availability, soil factors controlling availability, and fixation patterns of micronutrients in selected semi-arid alkaline soils on experimental settings designed to investigate micronutrient fate over short term (14 days) and long term (90 days). A total of five different soil series were used and micronutrient chemistry examined in single, mixed, and mixed-chelated systems. In the single system, approximately 4 % more Cu (39 % total) and 17 % more Zn (47 % total) were fixed between days 14 and 90. In the short term, micronutrient availability was influenced by OM (for Cu), and CaCO3, EC, and OM (for Zn), and in the long term by pH, available Zn, OM, and CaCO3 (for Cu), and pH and total P (for Zn). The reactions leading to the fixation of Cu and Zn in these soils were better described by the power function model (R2 = 0.80 - 0.90) and values of reaction rate constants revealed that Zn was fixed at a faster pace than Cu, particularly within the first 35 days. Within the mixed systems, approximately, 22 % more Cu was fixed in the non-chelated system within the first 14 days and 7 % more by day 90. For Zn, approximately 30 % more was fixed in the non-chelated system compared to the chelated system after the first 14 days and 18 % more by day 90. Findings suggest a decrease in the effectiveness of chelated micronutrient over time. In the non-chelated system, the fixation of Cu and Zn were positively correlated to each other in the long term (R = 0.93, P < 0.009, n = 6) and the short-term (R = 0.93, P < 0.009, n = 6), respectively. The chelated system on the other hand, revealed a similar but weaker relationship of Cu and Zn fixation in the long-term (R = 0.80, P < 0.06, n = 6). Reactions leading to the fixation of available Cu and Zn in the non-chelated systems were best described by the power function models (R2 = 0.91-0.95). However, within the chelated system, Cu fixation was better described by the second order model (R2 = 0.95), while Zn was poorly described by all the models examined (R2 = 0.66 - 0.70). The short and long term examinations conducted highlighted the significance of timing even when chelated micronutrients are applied. The reaction rates generated from this study can serve as important tools for micronutrient management and baseline data for further modeling of nutrient dynamics in these semi-arid alkaline soils of the SHP.



Micronutrients, Copper, Zinc, Semi-arid, Soils, Plant-availabilty, Fixation kinetics