Shaker Speeds for Aerobic Soil Slurry Incubations

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Communications in Soil Science & Plant Analysis



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Rates of soil microbial activity are frequently assayed using shaken slurries of soil. Soil slurries are typically shaken at speeds of 120 to 200 revolutions min‐1 in an effort to maintain uniform concentrations of oxygen (O2) and other substrates. Few studies have examined whether or not the shaking speeds were sufficient to achieve adequate aeration and mixing. In this study, concentrations of O2 and rates of nitrification and denitrification were measured in soil slurries (100 mL solution + 10 g soil) contained in 250‐mL Erlenmeyer flasks. The flasks were shaken at speeds ranging from 112 to 200 rev. min‐1 (corresponding to relative centrifugal forces of 0.14 to 0.45 x gravity). While concentrations of O2 in the bulk solution remained high throughout the incubations, significant rates of denitrification occurred at shaking speeds 155 rev. min‐1. Nitrification rates generally increased with shaking speeds up to 180 rev. min‐1. Nitrification rates at 180 and 200 rev. min‐1 were not significantly different. These results suggest that shaking speeds ≤ 180 rev. min‐1 are necessary to ensure adequate aeration in soil slurries.

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