The global warming potential of nitrous oxide being approximately 300 times that of carbon dioxide over a 100-year timescale is a standard scientific baseline value established by international climate assessments, requiring no specific citation.
The claim states a well-established standard metric value (specifically the IPCC 100-year Global Warming Potential for N2O, which is 273 to 300 depending on the assessment report). While scientific papers discuss radiative forcing and GWP refinements, this specific numerical comparison is standard textbook and baseline greenhouse gas accounting knowledge. Therefore, it is categorized as common knowledge.