Forms and pedogenic distribution of extractable iron in selected wetland soils in Nigeria
2000
Olaleye, A.O. | Ogunkunle, A.O. | Sahrawat, K.L.
The content of various forms of iron (Fe) (free, reducible, and organic) were determined by selective extraction methods in three wetland profiles between 1993 and 1995 seasons. The result showed that Fe distribution was in the order: dithionite (Fe(d)) > hydroxylamine (Fe(H)) > pyrophosphate (Fe(p)) iron in the three pedons. The hydroxylamine-Fe constituted between 10-42% (1993), 20-47% (1994), and 10-12% (1995) of the total free Fe oxides. The pyrophosphate-Fe, on the other hand, constituted between 0.2-1.0% (1993), 19-52% (1994), and 3-9% (1995) of the total free Fe oxides. Dithionite-Fe (total free iron oxides) content increases with the increasing depth, while hydroxylamine-Fe decreases, suggesting that larger proportions of Fe oxides are present as crystalline forms in the lower horizons. The active Fe ratios were generally high in the top soils and low in the subsoil. It ranged between 0.03 and 0.69 (1993), 0.05 and 68 (1994), 0.05 and 0.53 (1995) in all pedons. This suggests that poor drainage slowed down soil development. Highly significant correlations (0.1%) were evident between phosphorus (P) and organic carbon; ECEC and base saturation; Fe(H) and active Fe ratio. Significant correlations (1%) were also evident between Fe(2+) and organic carbon; P and Fe(H); ECEC and clay. Furthermore, significant correlations (5%) were also obtained between clay and Fe(d); pH and Fe(d); active Fe ratio and P; Fe(H) and clay; active Fe ratio and Fe(d).
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