Distribution of Free Iron and Aluminium Oxides in Selected Soils on Basement Complex Parent Rocks from South West Nigeria

Abstract

Twenty (20) soil samples from soils of basement complex parent rocks origin were collected to investigate
the distribution of free iron and aluminium oxides and their influence on soil chemical and physical
properties. Distribution of total free Fe and Al oxides of the soils samples were determined by ammonium
oxalate and citrate bicarbonate dithionite methods. The Fed was higher than Feo in all the locations. The
soil samples from Oyo State (Barrack) had the highest amount of Feo (1.6 g kg-1) while Ekiti (Ado Ekiti)
recorded the highest total free iron oxide (Fed) content (2.8 g kg-1 ). Both Crystalline aluminium oxide
(Alo) and amorphous aluminium oxide (Ald) were high in soil from Oyo state (Barrack). The highest ratio
of iron oxide (Feo/Fed) was obtained for soil from Oke oya (Oyo State). Significant correlation were
obtained between Fed and crystalline iron (Feo) (r = 0.788, P<0.01); Feo and Alo (r = 0.691, P< 0.01); pH
and organic carbon (r2 = 0.599, P<0.01); Fed and Ald (r2 = 0.585, P< 0.01) ; Alo and organic matter (r2
= - 0.57, P <0.01); CFe and exchangeable acidity ( r= 0.510, P< 0.05); Fed and Alo (r=0.494, P<0.01) ;
Feo and pH (r =- 0.487, P<0.05); CFe and organic carbon ( r = 0.471, P< 0.05); Organic carbon and
organic matter (r = 0.459, P< 0.01) ; Feo and Fed at (r = 0.453, P< 0.05) and Alo and available P (r=
0.446, P< 0.05).
This result shows that both Fed and Alo were extracting from the same pool and the soils were highly
weathered with little minerals as revealed by the low values of Feo. The low quantity of the crystalline
oxides in these soils is an indication of lack of accumulation of concretions, nodules and plinthites which
can make the soil unproductive. Organic matter, pH, exchangeable acidity, organic carbon and available
P had strong influence on the distribution of iron and aluminium oxides in the study soil.