Accumulation and consumption of odorous compounds in feedlot soils under aerobic, fermentative, and anaerobic respiratory conditions.

Agricultural odors present an increasingly difficult challenge to livestock producers, yet very little information is available on the microbiology of odor production or microbial factors that regulate the emission of odors. This study examined the microbial potential for odor production and odor consumption in two soils from a cattle production facility in central Nebraska. The two soils tested were collected from a feedlot pen and a runoff ditch below the pen and contained high- and low-fecal matter content, respectively. These soils were tested for their ability to produce and consume a mixture of VFA and aromatic compounds (phenols and indoles) under aerobic, fermentative, and anaerobic respiratory conditions, with NO3-, Fe(III), Mn(IV), and SO4(2-) serving as anaerobic terminal electron acceptors, over a 6-wk incubation. The pen soil had greater (P < 0.05) initial total VFA content (40 micromol/g soil) and produced more VFA during incubation than the feedlot ditch soil, whereas total aromatic compound concentrations were not significantly different between soils. The general pattern of odor compound accumulation and consumption did not differ between soils. Oxygen and nitrate treatments produced very little VFA and consumed acetate more rapidly than the other treatments, which produced large quantities of short-chain VFA and consumed acetate only after all other VFA were consumed. When VFA and aromatic compound consumption was compared across all the treatments, aerobic incubation proved most effective, and all compounds were rapidly consumed by the second day of incubation. Of the anaerobic treatments examined, nitrate proved most effective, followed by Fe, with VFA consumed by d 5 and 21, respectively. Anaerobic incubation with sulfate produced more VFA than the fermentative incubation, and anaerobic incubation with oxidized Mn produced the largest quantities of VFA, which remained high throughout the six-wk incubation. Aromatic compounds were more easily consumed aerobically and were only slowly consumed in the anaerobic treatments. We conclude from this study that cattle feedlot soils possessed a varying, potentially exploitable capacity for odor consumption when alternate electron acceptors were available.