Background and aims <p>Double-cropped and regenerated crop managements have great potential to increase oat forage production through efficient utilization of water and solar resources. However, the interaction of crop management and the nitrogen (N) input on the forage yields, water and N use efficiency, as well as soil N content are not well documented.</p> Methods <p>A four-year field experiment was established with 0, 75, and 150&#xa0;kg N ha⁻¹ in the summer season under double-cropped and regenerated oat managements, and similar N inputs were in the previous spring season.</p> Results <p>The double-cropped management increased forage yield and water use efficiency by 27–34% and 4–12% respectively in normal years, while it decreased total soil N content as well as nitrate and ammonium contents compared with the regenerated crop management. Low N input reduced the forage yield and soil N content in both crop managements, while it had higher N use efficiency (NUE). Applying 75 and 150&#xa0;kg N ha⁻¹ increased forage yield by 13–14% and 18–22%, respectively, whereas the former resulted in 11% higher NUE than the latter in both crop managements. Remarkably, due to the tradeoff between N yield and NUE, similar equivalent sustainable N management indexes were detected between N inputs, and their low values indicated other field managements to increase both forage yield and NUE simultaneously.</p> Conclusion <p>The double-cropped management demonstrates significant potential for improving forage yields, water and N use efficiencies, necessitating further efforts to optimize sustainable N management in oat production.</p> Graphical Abstract <p></p>