Date of Graduation


Document Type


Degree Type



Davis College of Agriculture, Natural Resources and Design



Committee Chair

Louis M. McDonald.


Microbial Fe-reduction in pasture soils may be of agronomic importance, because it has been shown to influence P cycling. The present study investigated the behavior of Fe and P in an intermittently wet, Appalachian pasture soil during a 42 day anaerobic incubation. Native humic acid (HA) extracted from the sampling location and anthraquinone-2,6-disulfonic acid (AQDS) were used in the experiment to determine their electron-mediating effects on Fe(III) reduction and P solubilization over time. Extracted HA and the International Humic Substance Society (IHSS) Elliott Soil HA standard were compared using 13C-NMR, FT-IR, SEM, and CHNS analysis. Soil samples treated with 1.24 g native HA/kg dry soil and 0.2 g AQDS/kg dry soil displayed the highest, most similar, solubilized P rates during the anaerobic incubation. However, the soil alone, without an added electron mediator, was able to release biologically significant concentrations of P to solution at Eh values between 0 and -200 mV. Total soluble P increases were strongly related to soluble Fe(II) increases over time. Field Eh measurements, relative to naturally occurring seasonal changes, are also reported. The purpose of this research was to further define the mechanisms of Fe and P cycling in temperate, pasture soils.