Mn Oxide Affects Nitrification and N2o Emissions in a Subtropical Rice Soil with Variable Water Regimes.

Paddy soils comprise the largest anthropogenic wetland land area on earth. The crop management-induced redox cycles lead to formation of distinct soil layers characterizing Mn distribution/redistribution. The role of Mn Oxides in nitrification and N₂O emissions were investigated to validate the hypothesis that Mn oxides play important roles in nitrification and denitrification for different water regimes subtropical rice soils. The nitrification process was simulated using zero- or first order kinetic models and N₂O emissions under different soil moisture contents were analyzed by gas chromatography. Results showed that net nitrification rates did not differ significantly after MnO₂ addition for 50% and 100% Water-Holding Capacity (WHC) moisture content, but rates increased significantly at 200% WHC. N₂O emission increased as soil moisture content increased, but was retarded at 100% and depressed at 200% WHC by MnO₂, respectively. MnO₂ increased nitrification rates and decreased N₂O emission rates only at 200% soil moisture content, implying that MnO₂ may play a role as an electron acceptor under anaerobic conditions in N cycling in subtropical rice soils.

Key Words: paddy soil; nitrification dynamics; manganese; N₂O emission; denitrification; electron acceptor