Asian Journal of Soil Science and Plant Nutrition

Studies on the total and available forms of iron and zinc in some selected soils of Akwa Ibom State were conducted between 2014 and 2015. Twenty-five surface (0-20 cm) composite soil samples formed from alluvia deposits, beach ridge sands, coastal plain sands, sandstones and mangrove swamp parent materials were used. Total contents of Fe and Zn were assessed by combined acids digestion method while, the available forms were determined using four chemical extractants (Coca-cola, 0.01M HCl, 0.05M EDTA and 1N NH4OAc). The results of the studies show that, parent materials did influence the contents of total and available Fe and Zn in the soils. Total Fe and Zn in the soils were high with values which varied widely between 237.20 and 452.87 mgkg^-1 and, 280.21 and 472.63 mgkg^-1, respectively. The extractable Fe and Zn values were low and varied from 9.00 to 12.66 mg kg^-1 and 2.46 to 3.81 mgkg^-1, respectively. HCl method extracted the highest content of Fe (8.70 mgkg^-1) followed by Coca-cola method (6.18 mgkg^-1). On the other hand, Coca-cola method extracted the highest content of the Zn (4.41 mgkg^-1) followed by HCl method (3.64 mgkg^-1). One normal NH4OAC extracted the least amount of Fe (4.77mgkg^-1) and Zn (2.16 mgkg^-1) relative to the other extractants. The study further shows that, the comparative extraction capacity of these extractants followed the order: O.1N HCl> Coca-cola> 0.05M EDTA>1N NH4OAC. The extractants yielded significant relations between concentrations of Fe and Zn and the soil properties. Higher correlations (r) values of HCl-extractable Fe and Coca- cola-extractable Zn with soil properties on one hand and among the extractants on the other hand, were established respectively. This suggests that, the 0.01M HCl and Coca-Cola extraction methods (both acid) are recommended as the most suitable soil testing methods for the determination of available Fe and Zn in the soil. Practical applications of these findings suggest that soil testing laboratories and agronomists can adopt 0.01M HCl and Coca-Cola as cost-effective and efficient extractants for assessing plant-available Fe and Zn in tropical soils. The information can guide fertilizer recommendations and soil management practices, ensuring adequate micronutrient availability for crops, particularly in Zn- and Fe-deficient soils. Additionally, the study provides insights for environmental monitoring and soil fertility improvement strategies in Akwa Ibom State and similar agro-ecological regions.