Assessment of Dithionite and Oxalate Extractable Iron and Aluminium Oxides in Soils Supporting Raphia Palms at Nifor Main Station

The oxides of iron and aluminium are known to affect the physical and chemical properties of soils such as ion adsorption, aggregate stability, phosphorus sorption and charge characteristics. This study was conducted to provide information on the status of free oxides in both soils of the Inland Valley and a well drained Upland soil at the NIFOR main station. Twenty four (24) representative samples were obtained from twelve (12) mini pits sunk at the two locations. The samples were air-dried and analyzed for physico-chemical properties including iron and aluminium oxides using standard methods. The results indicated that Fed ranged from 5.86mg/kg to 151.38mg/kg at the Inland Valley and ranged from 11.13mg/kg to 34.46mg/kg at the Upland. The Fed values were higher than Feo values in both locations. The Feo/Fed ratio (diagnostic index ) values clearly distinguished the well drained Upland soil from the poorly drained Inland Valley as the values decreased with increased soil depth at the Inland Valley but increased significantly with increased soil depth at the Upland. There was no evidence of co-migration of clay with Fed in both locations though significant correlations were obtained between clay and clay/Fed ratio of Inland Valley and Upland with (r = 0.841, P < 0.01)and (r = 0.891, P < 0.01)respectively. Significant correlations were also obtained between Fed and Fed-Feo (r = 0.998, P < 0.01 ); Fed and organic carbon (r = 0.945, P < 0.01 ); Fed and clay (r = -0.720, P < 0.01); Fed and Clay/Fed ratio (r = -0.719, P < 0.01)Ald and Ald-Alo (r = 0.922, P < 0.01 ); Ald and Feo/Fed (r = 0.592, P <0.05 ); Ald and Clay/Fed (r = 0.628, P< 0.05 ); Alo and Ald-Alo (r = -0.653, P < 0.05 ); Fed-Feo and Clay/Fed (r = -0.724, P < 0.01 ); Fed-Feo and organic carbon (r = 0.948, P < 0.01 ); Fed-Feo and Clay (r = -0.736, P 0.01 ); Feo/Fed and Clay/Fed (r = 0.617, P < 0.05 )and Feo/Fed and Clay (r = 0.705, P < 0.01)at the Inland Valley. This trend of correlation continued at the Upland except that Ald was not correlated with Feo/Fed and Clay/Fed while Feo was correlated with Feo/Fed of Upland (r = 0.607, P < 0.05)and was not correlated with Feo/Fed of the Inland Valley. This study has revealed that the soils of NIFOR main station are highly weathered soils and contained little weatherable minerals as revealed by the low amounts of Feo. The low amounts of the crystalline oxides in these soils reveal a lack of accumulation of concretions, nodules and plinthites which lead to deterioration of physical and chemical properties of soils.