ABSTRACT

The study was conducted during May 2023 in some locations in the Erbil plain and Bardarash sub-district of the Kurdistan Region of Iraq to examine the relationships between zinc (Zn) availability and several key soil parameters - total CaCO3, active CaCO3, phosphorus, and bicarbonate ions (HCO₃⁻) - in calcareous soils. Zinc is an essential micronutrient required for optimal plant growth and physiological functioning, playing vital roles in enzyme activation, protein synthesis, regulation of growth hormones, and numerous metabolic pathways. However, Zn availability in soil is highly variable and strongly affected by multiple interacting chemical and physical properties, particularly in calcareous soils, where high carbonate content often limits micronutrient mobility and uptake. Thirteen paired soil and plant samples were collected to assess both soil Zn concentrations and corresponding plant uptake. The results revealed considerable spatial variation in soil Zn levels. Sample S6 contained the lowest Zn concentration (0.13 mg.g⁻¹), while sample S7 exhibited the highest value (0.65 mg.g⁻¹). Notably, S7 also recorded the lowest total CaCO₃ content (10.9%) and active CaCO₃ content (5.0%), whereas S6 recorded among the highest total CaCO₃ content (35.8%), consistent with an inverse relationship between carbonate content and Zn availability. Statistical analyses identified significant negative correlations between Zn concentration and active CaCO₃ (r = –0.52 in soil, r = –0.578 in plant, p < 0.05) and total CaCO₃ (r = –0.565 in soil, r = –0.613 in plant, p < 0.05) across both soil and plant datasets, suggesting that elevated CaCO₃ levels markedly reduce Zn bioavailability, likely by enhancing Zn adsorption or precipitation within the soil matrix. Additionally, a highly significant positive correlation (r = 0.952, p < 0.01) was found between soil Zn and plant Zn content, indicating that plant uptake is closely governed by the soil's Zn status.