TABLE 1.

Rates of CH4 production, Fe3+ reduction, and SO42− reduction in unamended and ferrihydrite- and gypsum-amended rice field soil slurries within 30 days of anoxic incubation; inhibition time points of different processes; and contribution of different respiratory processes to total reducing equivalents formed

Soil treatmentProcess (day inhibition started)Product formation [μmol day−1 g−1 (days)]Reductant formed (μmol g−1)aTotal reducing equivalents formed [μmol g−1 (%)]b
MaximumInitialSteady-stateInhibited
No amendmentCH4 production1.25 (9)0.83 (4-10)0.5 (11-30)15.8126.2 (56.8)
Fe3+ reduction20.1 (2)11.6 (1-5)89.589.5 (40.3)
SO42− reduction0.33 (4)0.19 (1-5)0.86.4 (2.9)
Ferrihydrite amendmentCH4 production (3)0.38 (28)0.15 (3)0.08 (3-30)2.519.6 (9.0)
Fe3+ reduction26.0 (3)14.2 (1-7)4.8 (7-20)197.1197.1 (90.3)
SO42− reduction0.10 (4)0.05 (2-6)0.21.6 (0.7)
Gypsum amendmentCH4 production (7)0.84 (6)0.53 (4-10)<0.01 (11-22)4.939.0 (17.9)
Fe3+ reduction18.6 (2)11.4 (1-5)103.5103.5 (47.4)
SO42− reduction0.69 (14)0.27 (4-12)0.5 (13-26)9.576.0 (34.8)
  • a Amount of either CH4 or Fe2+ formed or SO42− reduced.

  • b The amount of product formed by each process was normalized to reducing equivalents of [H] as follows: from CH4 production (8 [H]), dissimilatory Fe3+ reduction (1 [H]), or SO42− reduction (8 [H]) to S2−. SO42− reduction was measured by following the disappearance of SO42−. The contribution of NO3 reduction was neglected (<20 μM present initially).