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 co nsumption in two soils from a cattle production facility in central Nebrask a. The two soils tested were collected from a feedlot pen and a runoff ditc h below the pen and contained high- and low-fecal matter content, respectiv ely. These soils were tested for their ability to produce and consume a mix ture of VFA and aromatic com-pounds (phenols and indoles) under aerobic, fe rmentative, and anaerobic respiratory conditions, with NO3-, Fe(III), Mn(IV ), and SO42- serving as anaerobic terminal electron acceptors, over a 6-wk incubation. The pen soil had greater (P < 0.05) initial total VFA content ( 40 mu mol/g soil) and produced more VFA during incubation than the feedlot ditch soil, whereas total aromatic compound concentrations were not signifi cantly different between soils. The general pattern of odor compound accumu lation and consumption did not differ between soils. Oxygen and nitrate tre atments produced very little VFA and consumed acetate more rapidly than the other treatments, which produced,large quantities of short-chain VFA and c onsumed acetate only after all other VFA were consumed. When VFA and aromat ic compound consumption was compared across all the treatments, aerobic inc ubation proved most effective, and all compounds were rapidly consumed by t he second day of incubation. Of the anaerobic treatments examined, nitrate proved most effective, followed by Fe, with VFA consumed by d 5 and 21, res pectively. Anaerobic incubation with sulfate produced more VFA than the fer mentative incubation, and anaerobic incubation with oxidized Mn produced th e largest quantities of VFA, which remained high throughout the six-wk incu bation. Aromatic compounds were more easily consumed aerobically and were o nly slowly consumed in the anaerobic treatments. We conclude from this stud y that cattle feedlot soils possessed a varying, potentially exploitable ca pacity for odor consumption when alternate electron acceptors were availabl e.