Ammonium Production in Submerged Soils and Sediments: The Role of Reducible Iron

Abstract

Submerged soils differ considerably from their arable counterparts. Lack of oxygen and the reduced state of submerged soils cause this. Submerging a soil under water triggers a series of physical, chemical and biological changes that greatly affect the dynamics of soil fertility and its use for growing crops such as wetland rice. Due to lack of oxygen, the nitrogen (N) mineralization process in submerged soils stops at ammonium production and nitrification is at low ebb. Most rice soils, especially those in the tropics are rich in iron (Fe). Redox cycling of Fe exerts a wide-ranging influence on the biogeochemistry of submerged rice soils and aquatic sediments where Fe is abundant. This article critically assesses the literature on the role of reducible Fe, which participates in redox reactions in submerged soils, on ammonium production or N mineralization in submerged soils and sediments. The reduction of Fe and organic matter oxidation in submerged soils and wetland sediments are interdependent. Results with freshwater sediments have indicated a direct correlation between Fe(III) oxide reduction rate constants and initial rates of organic C mineralization. The role of reducible Fe on N mineralization or ammonium production is not clearly understood. However, recent research with diverse West African rice soils showed that ammonium production in submerged soils is highly significantly correlated to reducible Fe. The results demonstrated that organic matter and reducible Fe control ammonium production in submerged soils. There is a need for future research to further elucidate the role and involvement of reducible Fe on N mineralization or ammonium production in submerged soils and sediments.

Keywords:

• Ammonium production
• Iron redox couple
• N nutrition of plants
• Wetland soils and sediments
• Role of electron acceptors
• Organic matter
• Redox potential