Soil Redox and pH Effects on Methane Production in a Flooded Rice Soil

Abstract

Abstract Methane formation in soil is a microbiological process controlled by many factors. Of them soil redox potential (Eh) and soil pH are considered critical controls. A laboratory incubation experiment was conducted to study the critical initiation soil Eh, the optimum soil pH, and the interaction of Eh and pH on CH 4 production. The critical soil Eh for initiation of CH 4 production observed was approximately from −150 to −160 mV. Between ‐230 and −150 mV, the relationship of CH 4 production and soil Eh appeared to be negatively exponential ( Y = a 10 ‐bx , where Y is the CH 4 production rate, µg g ‐1 d ‐1 ; x the soil Eh, mV; and a and b are constants). The optimum pH of CH 4 production was near neutrality. A small decrease in pH resulting from the introduction of acidic materials significantly decreased CH 4 production. A slight increase in soil pH (about 0.2 unit higher than the natural soil suspension pH), however, resulted in an enhancement of CH 4 production by 11 to 20% and 24 to 25% at controlled Eh of ‐250 and ‐200 mV, respectively. Results suggest that a decrease in CH 4 emissions could be obtained by a small reduction in soil pH in Crowley soil (fine, montmorillonitic, thermic Typic Albaqualf).