Factors Influencing Oxygen Consumption Rates in Flooded Soils

Thirty‐seven surface soil samples varying in physico‐chemical properties were incubated under reduced (anaerobic) conditions to study the factors influencing oxygen consumption rates. Oxygen consumption rates were measured after introduction of a known amount of oxygen into a reduced (anaerobic) soil system and following the disappearance of oxygen as a function of time. The time dependence of oxygen consumption in all flooded soils could be described as a two‐phase first order reaction process. Rapid oxygen consumption during Phase I was followed by relatively slower consumption during Phase II. The first‐order rate coefficient ( k 1 , hour −1 ) for Phase I was approximately the same for all 37 soils evaluated, whereas each soil was characterized by a different rate coefficient ( k 11 , hour −1 ) for Phase II. The average value for k 1 was 0.15 hour −1 (coefficient of variation = 20%) while the values of k 11 ranged from 0.0027 to 0.054 hour −1 . Step‐wise regression analysis of the data showed that NaOAc‐extractable Fe of a reduced soil was the single best predictor of k 11 and also the fractional consumption associated with Phase I. Significant improvement in these regressions was obtained when total NH 4 ‐N content of the reduced soil, in addition to reducible Fe 2+ was considered.