Factors controlling nitrification and denitrification: a laboratory study with gel-stabilized liquid
1992
Petersen, S.O. | Neilsen, A.L. | Haarder, K. | Henriksen, K.
Nitrification and denitrification were studied in a millimeter-scale 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.
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