Profile Distribution of Iron and Zinc in Soils formed from Three Different Parent Materials in Akwa Ibom State, Nigeria

Abstract

The distribution of total and available levels of iron (Fe) and zinc (Zn) was studied in three major soil types derived from different parent materials in Akwa Ibom State. The parent materials were: Sandstone (SS), Coastal Plain Sands (CPS) and Beach Ridge Sands (BRS), respectively. Six representative soil profiles, two each for SS, CPS and BRS were dug. The soils from the different parent materials were sampled at different depths of 0 – 20, 20 – 40, 40- 60, 60 – 80, 80 – 100 and 100 – 120 cm. The soil samples were air dried, crushed and sieved using a 2mm sieve and stored in labeled bags for analysis. Laboratory analysis was conducted. The soils were strongly weathered, coarse in texture, acidic and generally low in fertility. Total Fe contents ranged from 365-1576mg/kg with sandstone soils having the highest mean of 1400mg/kg, followed by those of the coastal plain sand with a mean value of 883mg/kg and 485mg/kg for beach ridge sands. The total content of Zn followed the same trend ranging from 43 to 335mg/kg with a mean value of 246, 114 and 79mg/kg for the sandstone soils, coastal plain sands and beach ridge sand soils, respectively. Available Fe contents in the entire profiles ranged from 9.8 to 33.3mg/kg with sandstone having the highest mean value of 28.2mg/kg, followed by those of coastal plain sands with a mean of 14.7mg/kg and beach ridge sands with a mean of 12.2mg/kg. The available Zinc content followed the same trend. Available Zn content ranged from 4.2-20.0mg/kg with a mean value of 12.2, 9.3 and 6.5 mg/kg for the sandstone, coastal plain sands and the beach ridge sands, respectively. The distribution of the micronutrients in the soil profile was generally irregular, but in some profiles, it decreased with depth. The micronutrients were weakly correlated with organic carbon, clay and silt in the three parent materials. The available levels of the micronutrients in the soils were relatively high, having values above the critical levels of 4.5mg/kg for available Fe and 1mg/kg for available Zn. The result showed that the content of the two micronutrients were highest in sandstone soils, followed by that of coastal plain sands and least in the beach ridge sand. The high content of the available iron and zinc indicate possible toxicity effect to plant grown on these soils.