<p>Addition of organic material, such as plant litter, can strongly alter C and N turnover in soils and promote CO₂ and N₂O formation. This study aimed to elucidate the role of C availability on N turnover processes leading to N₂O formation under moderately dry conditions. We measured CO₂, NO, and N₂O fluxes and contributing processes from an arable and a grassland soil with four different treatments: 50% water-filled pore space (WFPS), 50% WFPS + Maize litter, 60% WFPS, 60% WFPS + Maize litter. CO₂ fluxes were partitioned into SOM- and litter-derived, and N₂O-forming processes were estimated applying a Bayesian mixing and fractionation model to infer source contributions and N₂O reduction rates. Further, we quantified bacterial and fungal population size, as well as genes involved in nitrification and denitrification at the end of the experiment. N₂O flux dynamics and contributing processes strongly differed between the C-limited arable soil and the C-rich grassland soil. In the arable soil, bacterial denitrification was consistently the main source of N₂O and strongly increased with addition of maize litter. In contrast, nitrification accounted for 51% of N₂O formation in the grassland soil without litter, while litter addition promoted fungal denitrification. We found higher N₂O emissions with higher total and SOM-derived CO₂ emissions confirming that availability of organic C from SOM and litter are important controls of N₂O losses. However, neither soil organic C content, nor litter addition, nor soil moisture alone were appropriate to predict the main N₂O-forming process. Therefore, our study emphasizes the need to disentangle and quantify N₂O-forming processes to develop successful mitigation strategies.</p>