Wet Soil Redox Chemistry as Affected by Organic Matter and Nitrate

Wet soil microcosms were established to determine effects of organic matter and nitrate additions on microbial respiration and redox potentials. Organic matter (1%) and nitrate (100 ppm and 200 ppm) treatments were applied in factorial combination. Soil pH, redox potential, and CO2 emissions were measured. Data were analyzed by ANOVA for repeated measures and separately by sampling day. Addition of organic matter significantly (P < 0.05) and consistently increased CO2 emissions and decreased redox potentials. On Day 42 nitrate significantly (P < 0.05) increased redox values. This study indicates a tendency for organic matter to decrease soil redox potential both in absolute terms and relative to the suboxic-anoxic boundary. Our findings portend that additions of organic matter may quickly and markedly decrease soil redox potentials and increase CO2 emissions in wetlands, whereas additions of nitrate may have complex and sporadic effects on redox potentials.