Phosphorus Behavior in Flooded-Drained Soils. II. Iron Transformation and Phosphorus Sorption
1989
Sah, R. N. | Mikkelsen, D. S. | Hafez, A. A.
Effects of flooding periods (FP), organic matter (OM) and temperature treatments during flooding on Fe transformation in flooded-drained (FD) soils were studied on four soils representing wide variations in the effect of FD conditions on P sorptivity. The soils were extracted in sequence with ammonium oxalate at pH 6 (amorphous FeA) and at pH 3 (amorphous FeB), and with dithionite-citratebicarbonate reagent (free Fe oxides). The amorphous FeA fraction increased with FP, OM treatment, and elevated temperature. In soils with low amorphous-Fe to free-Fe-oxide ratio, both amorphous FeA and free Fe oxides increased at the expense of amorphous FeB as the FP increased. In soils with low amorphous-Fe to free-Fe-oxide ratio, both amorphous Fe fractions (A and B) increased at the expense of free Fe oxides as FP increased. For all soils, the Fe transformation during soil flooding was accelerated by OM and high-temperature treatments, both of which contributed to a decreased redox potential in the soil. Amorphous FeA fraction correlated well with P sorption under all combinations of OM and temperature in each soil, while other Fe fractions correlated well only under certain conditions. Results suggest that the nature and the magnitude of Fe transformations in these FD soils depend on interacting effects of FP, OM, and temperature. Contribution from pep. of Agronomy and Range Science, Univ. of California, Davis.
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