Nitrogen is an essential nutrient for producing food and managing the nitrogen cycle has been identified by the National Academy of Engineers (NAE) as one of the Grand Challenges for Engineering in the 21<sup>st</sup> Century. A key component of the nitrogen cycle is denitrification which reduces nitrate and nitrite. Usually considered a biological process, denitrification can lead to several products. When microbially facilitated, denitrification usually leads to the formation of nitrogen gas, which is harmless. Abiotic denitrification (also known as chemodenitrification) is the reaction of nitrate and/or nitrite with soil minerals, such as iron oxides. Reduction by iron oxides can lead to more harmful products such as nitrous oxide, which is a potent greenhouse gas. Little is known about the rate of abiotic denitrification in comparison to biotic denitrification in agricultural soils, which can lead to uncertainty in nitrogen cycle models which typically only take biotic denitrification into account. Here we address whether chemodenitrification is a significant part of the denitrification cycle compared to biotic denitrification. To quantify rates of chemodenitrification we will react nitrite with aqueous Fe(II) and four iron minerals; goethite, hematite, ferrihydrite, and magnetite. Denitrification products such as nitrous oxide will be measured using gas chromatography. Biotic denitrification rates will be measured in pure cultures of known denitrifying bacteria. Each of these experiments will give dominant reaction products and rates, which can then be compared to each other. Our results will provide insights into factors controlling denitrification rates and products in agricultural soils.

Role of abiotic and biotic denitrification in agricultural soils

255th National Meeting (2018)

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