Underlying mechanisms behind nitrous oxide emissions in oilseed radish, Raphanus sativus var. oleiformis, and Phacelia tanacetifolia

Abstract: Greenhouse gases are a driving force of climate change and the annual greenhouse gas emissions were higher between 2010-2019 than any other time in human history (Skea et. al. 2022). Cover crops are used to mitigate the effect of climate change, but recent studies indicate that the use of the cover crop oilseed radish results in significantly larger emissions of nitrous oxide (N2O) compared to other cover crops (Dörsch et. al. 2022; Müller Júnior et. al. 2019; Olofsson and Ernfors 2022; Thomas et. al. 2017). Results from Olofsson and Ernfors (2022) study showed that Raphanus sativus var oleiformis (OR) causes significantly higher emission of N2O compared to Phacelia tanacetifolia (PH) even though the quality and quantity were similar. The hypothesis in this study was that the glucosinolates in OR provides a carbon source for denitrifying bacteria, thus causing a significantly higher N2O emission compared to PH. The hypothesis was tested in a laboratory setting during 32 days of gas measurement with plant material of OR and PH incubated with and without added glucose. Surprisingly, aboveground plant material of PH showed highest emissions throughout the study. The result of this study could not confirm the hypothesis since added glucose did not affect the N2O emission. In further studies, it is recommended to increase the number of replicates and optimize the methodology to be able to draw any conclusions.