Fractionation of Iron, Managanese, Aluminum, and Phosphorus in Selected Sandy Soils under Citrus Production
1997
Zhang, M. | Li, Y. C. | Calvert, D. V. | Alva, A. K.
The sorption and downward transport of trace metals and phosphate in soils are dependent, in part, on the distribution of various forms of Fe, Al, and Mn. The objectives of this study were to investigate (i) the distribution of various forms (exchangeable, organically bound, associated with Mn oxide, amorphous, and associated with crystalline Fe oxide forms) of Fe, Mn, Al, and P in the surface horizons, and (ii) the distribution of these elements in different depth horizons in six soil series in Florida representing Spodosols, Alfisols, and Entisols. Variation in concentration of total Fe with depth of soil was significantly correlated with clay content. Greater than 60 and 80% of total Fe was present in the amorphous and crystalline Fe oxide forms in soils with pH ≤ 6.5 and pH > 6.5, respectively. Total concentration of Mn was lower than that of Fe or Al in all the soils, and it changed very little with depth of sampling. Manganese in the surface horizon was present predominantly as the organically bound form in the Spodosols and as organically bound, oxide, and amorphous forms in the Alfisols and Entisols. The distribution of total and oxalate-extractable P was significantly related to the content of amorphous Al and Fe and crystalline Fe oxides in the soils. The distribution of various forms of the metals and P was significantly influenced by the soil pH and organic matter content. In the surface horizon soils, Mn and Al were present predominantly as organically bound forms at pH < 6.5 or as Mn oxide and amorphous associated forms at pH > 6.5.
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