Year of Publication

2013

Degree Name

Master of Science (MS)

Document Type

Master's Thesis

College

Agriculture

Department

Plant and Soil Science

First Advisor

Dr. Chris Matocha

Abstract

New evidence shows iron(II) oxidation is strongly coupled to nitrate reduction under anaerobic conditions in freshwater sediments and agricultural soils. However, the contribution of iron(II) oxidation to nitrate reduction is unknown. Furthermore, oxidation of manganese(II) by nitrate has been largely overlooked. This study investigated nitrate-dependent iron(II) and manganese(II) oxidation in an agricultural soil (Sadler silt loam) using stirred-batch kinetic techniques with native soil organic carbon (SOC) as the electron donor and included addition of amendments (hydrogen gas and wheat residue). In the presence of native SOC, nitrate-dependent Fe(II) and Mn(II) oxidation occurred at early stages of the reaction while organic carbon participated at longer times. Contributions of iron(II) and manganese(II) oxidation to nitrate reduction were 19% and 25%, respectively. This is significant in light of excess SOC relative to total Fe and Mn in the Sadler soil. Addition of hydrogen gas lowered the contribution of iron(II) oxidation to nitrate reduction to 10%, while addition of plant residue raised this value to approximately 55%. Manganese(II) oxidation contributed 50% to nitrate reduction under hydrogen amended conditions. These coupled processes involving Fe(II) and Mn(II) oxidation are an underappreciated aspect of the nitrogen cycle and merit consideration in future studies.

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