Decades ago, denitrification was considered as an economically negative process leading to loss of nitrate. In the seventies, the economic aspect was overshadowed by the link of denitrification with emission of harmful gaseous N-compounds. In addition, paddy fields as well as flooded areas and wetlands were quickly identified as ecosystems producing large amounts of methane and nitrous oxide. More recently the interaction between emission of both gases is being studied. Both gases are emitted at different redox potential conditions, allowing searching for a critical redox potential with minimal formation of both, as such mitigating the cumulative global warming potential. Organic matter as electron donor can play a critical role as regulator of the aeration status of soils. For several decades the use of carefully controlled pH-Eh microcosms was extremely helpful to unravel complex N-transformation processes and their interaction with the carbon cycle, thanks to the brilliant ideas of Bill Patrick.