A three-electrode system and a precision potentiostat were used in the
electrolytic reduction of suspensions of two soils. A saturated calom
el reference electrode served as a potentiometric probe of the interfa
cial potential at the surface of the working electrode. Solution resis
tance between these two electrodes was minimized by suspending the soi
ls in 1 M KCl. In one set of experiments electrolysis was carried out
for 4 hours at a range of applied potentials, while in another set of
experiments electrolysis at one of two applied potentials was continue
d until an apparent equilibrium had been reached. Faradic current, sus
pension redox potential (Eh) and pH, and solution concentrations of Fe
were measured as functions of time and applied potential. As evidence
d by the appearance of Fe in solution, reduction of Fe (III) compounds
began to occur at an applied potential of -48 mV vs. the standard H e
lectrode. This is more negative than the potentials at which Fe first
appears in flooded soils. The pH values of the suspensions increased a
s the applied potentials became more negative and as the duration of e
lectrolysis increased. Measured suspension Ehs were initially lower th
an the applied potentials, but after 20 h of electrolysis these two qu
antities had similar values, suspension pH and solution concentrations
of Fe had reached relatively constant values, and the faradic current
had declined to background levels. Approximately 75% of the citrate-b
icarbonate-dithionite-extractable Fe of both soils had been reduced af
ter 20 h of electrolysis at an applied potential of -359 mV. This elec
trolytic reduction technique potentially offers an alternative in the
study of soil redox process under controlled Eh condition.