title: Factors controlling nitrification and denitrification: A laboratory study with gel-stabilized liquid cattle manure.
abstract: Nitrification and denitrification were studied in a millimeterscale microenvironment using a two-phase system with a liquid manure-saturated layer. Samples consisted of liquid cattle manure and air-dried soil stabilized with silica gel, placed between two aerobic soil phases with a water content near field capacity. A high potential for NH4 (+) oxidation developed within 0-2 mm distance from the interface, and NH4 (+) diffused only 10-20 mm into the soil. Some NH4 (+) was probably immobilized by microorganisms in the soil between 0 and 4 days, after which nitrification was the only sink for NH4 (+). A potential for denitrification developed within the manure-saturated zone. Maximum rates of both potential and actual denitrification were recorded by Day 4, but denitrification continued for at least 2-3 weeks. The potential for nitrification peaked after 14 days. When the pH of the manure was adjusted to 5.5, nitrification was reduced close to the interface, and NH4 (+) penetrated further into the soil before it was oxidized. The pH adjustment had an inhibitory effect on denitrification: Both potential and actual rates of denitrification were almost eliminated for several days. The size of the manure-saturated layer strongly affected denitrification losses. With layers of 8 and 16 mm thickness, losses equivalent to 33 and 40% of the original NH4 (+) pool, respectively, were estimated. When manure corresponding to a 12 mm layer was homogeneously mixed with the soil, only 0.3% was lost.
authors.affiliation: Laboratory of Environmental Engineering, University of Aalborg, Sohngaardsholmsvei 57, DK-9000, Aalborg, Denmark.
authors.forename: S O
authors.initials: SO
authors.lastname: Petersen
authors.forename: A L
authors.initials: AL
authors.lastname: Nielsen
authors.forename: K
authors.initials: K
authors.lastname: Haarder
authors.forename: K
authors.initials: K
authors.lastname: Henriksen