Free Oxide Status and Distribution in Soils of some Economic Palms in selected areas of Delta State, Nigeria

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Abstract

The status and distribution of free oxides in soils of selected economic palms such as Coconut, Oil and Raphia palms in some areas of Delta state (Owah-Abbi, Agbor, Asaba, Bomadi, Sapele, Ughelli and Warri), Nigeria. Composite top and subsurface soil samples were randomly obtained at two soil depths of 0 - 45 cm and 45 - 90 cm from the various locations; air dried, sieved through a 2- mm sieve and analyzed for physical and chemical properties. The acid-ammonium oxalate and dithionite-citrate-bicarbonate methods were used to extract the free oxides from the samples. Free oxides obtained from both extractants were compared. Results indicated that crystalline forms of Fe oxide (Fed) were higher than the amorphous forms (Feo) in all the locations and generally increased with increased soil depth except in Sapele soils where it slightly decreased with depth. There was evidence of a co-migration of Fed with clay in some of the locations. The active Fe ratio Feo/Fed values were fairly constant throughout the locations and decreased with increasing soil depth indicating the presence of purely crystalline Fe oxide. The high amounts of the crystalline forms in these soils ranging from 110.00 mg/kg to 337.50 mg/kg in the surface soils to 121.90 mg/kg to 559.00 mg/kg in the sub surface soils indicated a possible formation of plinthites and concretions in the rooting depth. This study has shown that some of the locations of Delta state could become unsuitable for the cultivation of economic palms due to the high amounts of free iron oxides that harden irreversibly on exposure. Continuous vegetal cover on the soils of these palms is suggested as a way of reducing the formation of plinthites in the soils of these locations.

Keywords: economic palms, Delta state, free oxides, oil palm, Raphia palms

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