Investigation of Fe(II) and Mn(II) involved anoxic denitrification in agricultural soils with high manganese and iron contents

Purpose: Soil denitrification rates and the roles Mn(II) and Fe(II) played as alternative electron donors were investigated by performing anoxic incubation experiments, using agricultural soils from Guangxi Autonomous Region, South China. Materials and methods: The dynamic of Mn(II) and Fe(II), electron contributions of Mn(II) and Fe(II) to denitrification, potential denitrification capacity, and gaseous-N composition were investigated. Results and discussion: The results indicated that Mn(II) and Fe(II) act as electron donors during the denitrification of paddy soils with high Mn and Fe contents. Coupling of denitrification and Fe(II) oxidation and coupling of denitrification and Mn(II) oxidation was found in paddy soils from the villages of Xialei. The maximum electron contributions of Mn(II) and Fe(II) to denitrification were similar, both reaching 18%, although the total Mn content was lower than the total Fe content. On the contrary, the roles and contributions of Mn(II) and Fe(II) to denitrification in soils from upland fields were not proved, even though all the studied agricultural soils had high Mn and Fe contents. Conclusions: The results suggested that Mn(II) is an important but previously ignored electron donor for denitrification and that Mn(II) plays a vital role in denitrification in paddy soils.