Forms of iron in soils on basement complex rocks of Kaduna state in northern guinea Savanna of Nigeria
The forms of iron extracted by different methods were studied in soils developed on four basement complex rocks within Northern Guinea Savanna of Nigeria namely: migmatite gneisses, older granite, quartzites and mica schists. The study shows that forms of iron generally decreased in the order of total elemental iron (FeT) determined by XRF > double acid extractable total iron (Fea) > dithionite extractable iron oxide (Fed) > oxalate extractable iron oxide (Fex) > pyrophosphate extractable iron oxide (Fep) > 0.1M HCl extractable micronutrient available iron (Feh). Variation in content of total irons (FeT and Fea) were not significant in the soils, but content of Feh, Fed, Fex and Fex/d significantly varied in the soils on the various parent materials. Therefore processes and extent of pedogenesis were considered to influence the variations resulting in recrystallization and increase in content of Feh and Fed in these soils. The significant correlation between various forms of Fe (Fea, Fed, and Fex) with active iron ratio further affirmed that as soils on basement complexes increase in their pedogenetic age, Fe content generally increases irrespective of total forms of iron. The strong correlation between FeT, Fea and Fed indicate that these forms of iron were extracted from similar sources.
Keywords: Iron, basement complex rock, pedogenesis, Northern Guinea Savanna, Nigeria.