Effects of Free Oxides on Potassium Fixation in Some Soils of Southern Nigeria.

Free oxides in soils usually have distinct electrochemical properties, generate both CEC and AEC as a consequence of the adsorption of proton and hydroxyl ions provide structural cementation in the soil. Thus, soil properties are influenced by the occurrence of free oxides. The effect of free oxides on the fixation of K in some soils of southern Nigeria was investigated. Incubation study was done using KCl and the extractability of K applied were examined over a period of time. A series of five sorption treatments (0.11, 0.22, 0.45, 0.90, and 1.8 cmol/kg) were prepared and applied in three sets to 2.5 g soils (15 soil samples per set). The first set of soil samples was extracted with 1 N NH4OAc extractant for K after 1 day of incubation. The second and third sets were extracted with the same extractant after 7 and 42 days of incubation, respectively. The amount of K fixed was determined and the correlation between K fixed and some soil properties was done. The amorphous iron oxides (Feo) correlated significantly (P <.01) with the amount of K fixed (r = 0.68**). Clay also had a highly positive and significant correlation with K fixed (r = 0.75**, P <.01). There was no relationship between the oxides of Aluminum (Alo and Ald) and K fixed, both having r-values of 0.220 and 0.391, respectively. Thus, the ability of these soils to retain K was due to the presence of clay and free iron oxide especially the ammonium oxalate extractable free iron oxide (i.e. amorphous iron oxide). [ABSTRACT FROM AUTHOR]