Nitrification and Coupled Nitrification‐Denitrification Associated with a Soil‐Manure Interface

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Abstract
Nitrification and denitrification in soil often occur in close proximity so that a substantial part of the NO−3 formed by nitrification afterwards diffuses to the anaerobic denitrification zone where it is reduced to N2. The stable N isotope based isotope pairing method was used to study nitrification and coupled nitrification‐denitrification associated with a manure hot‐spot in soil contained within a diffusion chamber. During the 3‐wk incubation period, a very active nitrification zone developed within 0.7 to 1 mm from the aerobic‐anaerobic soil‐manure interface, and within this thin zone, all NH+4 liberated from the manure was oxidized. The short distance between the nitrification zone and the anaerobic manure facilitated coupled nitrification‐denitrification, which turned out to be the main sink for liberated inorganic N with maximum rates of 140 nmol N‐N2 cm−2 h−1, thereby removing 90% of the inorganic N liberated during the incubation period. The applicability of the isotopic pairing method was verified by using variable concentrations of 15NO−3 and by selectively inhibiting nitrification with acetylene. The change in 14NO−3 profile following addition of acetylene was simulated by a diffusion reaction model to obtain estimates of the underestimation of denitrification by use of the commonly used acetylene blockage technique. Incubation periods with acetylene of 1, 3, 6, and 12 h reduced the coupled nitrification‐denitrification rate to 46, 25, 16, and 10%, respectively, of the original rate, and use of the acetylene technique for determining denitrification in manure‐amended soils thus cannot be recommended.
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  • Carlsbergfondet

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