Interactions of Iron with the Nitrogen Cycle

A long-standing enigma in agriculture is the fate of missing nitrogen in soiL Fie]d conditions at the surface and subsoil conducive for biological denitrification are also environments where other potential reductants are known to accumulate such as ferrous (Fe(II» iron. It is intriguing that groundwater and soils containing Fe(lI) have little or no nitrate. Abiotic denitrification by naturally occurring Fe(II) could playa significant role in coupling the redox cycles ofN and Fe in soil environments, yet there is very little mechanistic information available in this regard. Accordingly, the overall goal of this proposed study is to investigate the role of naturally occurring reactive ferrous iron species in nitrate reduction. This goal will be achieved by first collecting fundamental kinetic data on nitrate removal by solid and adsorbed ferrous iron over a range of experimental conditions in the laboratory using advanced spectroscopic tools. We will then conduct stirred batch studies on two surface and subsoils with fluctuating water tables to delineate the dynamic nature of the redox front and elucidate areas that support nitrate removaL These results will help answer questions about whether nitrate reduction is coupled to ferrous iron oxidation. Understanding this relationship should move us closer to the goal of incorporating nitrate transformation pathways into predictive fate models to increase nitrogen fertilizer use efficiency and protect the environment.