Influence of topography on pedologic forms of iron in basement complex soils of Giwa Local Government Area, Kaduna State, Nigeria

A toposequence formed on Basement Complex rocks in Giwa Local Government Area of Kaduna State was studied with the aim of investigating the influence of topography on the distribution of pedologic forms of iron in the area. The area, which spanned 15.55 ha was delineated into upper slope (US), middle slope (MS) and lower slope (LS) positions. Two profile pits were sunk in each slope position and described following standard procedures. Soil samples were also collected for determination of selected physical and chemical soil parameters in the laboratory. The results showed that topography had significant influence on sand, silt and organic carbon (OC) contents across various slope positions. Sand content was highest on US (711.87 g kg-1) and lowest on LS (671.20 g kg-1).Conversely, silt, clay and OC contents were higher on LS than on MS and US. This was attributed to translocation of finer particle sized and organic materials down the slope as preconditioned by topography. Si/C ratio was higher on LS, indicating advancement in soil development, compared to MS and US. Oxalate extractable iron (Feox) was highest in LS (0.26%), followed by MS (0.23%) and US (0.22%). Dithionite extractable iron (Fed) was highest in the US (0.85%), followed by LS (0.66%) and MS (0.65%). The Feox/Fed ratio varied thus MS (0.43), > LS (0.43) >e US (0.27). The higher ratio of Feox/Fed on LS and MS indicated long-term weathering and soil maturation, in comparison with US. Fed/Clay ratio indicated higher affinity of Fed to clay minerals on MS (33.66), compared to LS (25.27) and US (19.06). Suggestion for further studies include exploring clay mineralogy, organic matter decomposition and redox processes, as these factors may also affect iron dynamics in soils.