FLOOD-INDUCED CHEMICAL TRANSFORMATIONS IN CALCAREOUS AGRICULTURAL SOILS OF SOUTH FLORIDA

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Abstract
Chemical transformations that occur under flooded conditions in two limestone soils from flood-prone agricultural areas of south Florida were investigated. Redox potential and pH of Krome very gravelly loam and Chekika very gravelly loam soils were monitored over a 5-week submergence period. Within 2 days of flooding, redox potential decreased to −150 mV and −300 mV for the Krome and Chekika soils, respectively, and by day 21 it had stabilized at about −165 mV for all treatments. The initial pH values of the Chekika and Krome soils was 7.9 and 7.5, respectively, but after 3 weeks of flooding the pH of both soils had stabilized at about 7.25. Samples of both soils were subjected to aerobic (field capacity moisture content, nonflooded) or anaerobic (submerged in water under N atmosphere, flooded) incubation in serum bottles. After 0, 1, 3, 5, and 7 weeks of incubation, concentrations of K, Fe, Mn, Mg, Ca, NH4+, NO3− and P were determined. Before incubation, concentrations of Mn and Fe were about 1–2 μg/g soil for both soils. After 7 weeks of flooding, extractable Mn and Fe increased 50-fold and 30-fold, respectively, for the Krome soil and 7-fold and 15-fold, respectively, for the Chekika soil. With aerobic incubation, Mn decreased and Fe increased slightly in both soils. Extractable Mg and Ca increased in both soils regardless of incubation treatment, but flooding resulted in higher concentrations of Mg and lower concentrations of Ca than aerobic incubation by week 7. For both soils, K increased regardless of incubation treatment, whereas P decreased, but decreased more rapidly with flooding. Extractable NO3− decreased with flooding but increased with aerobic incubation, where NH4+ decreased with aerobic incubation but increased with flooding. The data obtained from this study indicate that annual, cyclical flooding may have potential for alleviating crop deficiencies of minor elements which is a major production expense in these soils. © Williams & Wilkins 1991. All Rights Reserved.

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