Date of Award


Document Type


Degree Name

Doctor of Philosophy (PhD)


Plant, Enviromental and Soil Sciences

First Advisor

Wayne H. Hudnall


Moreland clay (very fine, smectitic, thermic, Oxyaquic Hapluderts) derived from Red River alluvium does not exhibit redoximorphic features, though it is saturated for more than 2 months during the growing season. Sharkey clay (very-fine, smectitic, thermic Chromic Epiaquerts) derived from the Mississippi River alluvium exhibits redoximorphic features. The objectives of this study were to determine the effects of energy sources and adjusted pH on Eh, pH, and iron transformation on these two Vertisols in Louisiana. Laboratory analysis was used to evaluate the factors controlling the formation of redoximorphic features. The first experiment was designed to predict the effects of 10 mg/kg sucrose and adjusted pH on the changes in Eh and pH during alternating saturation and drying treatments. DCB, acid-oxalate, and sodium pyrophosphate reagents were used to evaluate iron transformation. The second experiment evaluated different sucrose concentration effects, from 0.25 to 20 mg/kg on pH and Eh. Methods used to evaluate organic carbon were also tested. The third laboratory experiment measured the redox potentials and chemical properties of the interstitial water at three different depths to correlate the relationship among Eh, pH, and redoxic couples while evaluating the reduction sequence and Fe oxide stability. Results indicated that: (1) Mn and Fe can't be reduced in soils with an insufficient energy source, and pH and soil color did not change during 3 weeks of flooding; (2) soil pH and Eh were controlled by the concentrations of organic carbon, types and concentrations of inorganic compounds, and fermentation; (3) selective chemical analysis can evaluate Fe transformation; (4) three different methods used to evaluate the concentrations of organic carbon failed to explain the change in Eh; (5) Eh, pH, and the concentration of Fe and Mn ions in the interstitial water failed to satisfy the Nernst equation; and (6) anaerobic microbes used nearby inorganic compounds as electron acceptors.