The use of cover crops, combined with low N fertilization and no-tillage, reduces the environmental impacts of agriculture. Legume cover crops provide N to the agroecosystem and allow N fertilization to be reduced without losing productivity, but may also increase nitrous oxide (N₂O) emissions. Our main objective was to evaluate the impact of using oats, vetch, and oats+vetch mixture as cover crops on N₂O emissions and summer crop yields in a maize–soybean rotation with low N fertilization to maize (32 kg N ha⁻¹) under no-tillage. We also studied how the different cover crops affected soil variables related to N₂O emissions. For the treatments that included vetch (vetch and oats+vetch), plots without N fertilization were included to evaluate if N₂O emissions and crop yield were increased by low-rate N fertilization after a legume cover crop. We measured N₂O emissions using static chambers in a long-term experiment located in the Argentine Pampas. We selected measurement periods in which high N₂O fluxes were expected to evaluate the effect of the different cover crops during these hotspots. In the early stages of maize and soybean, the use of vetch as a cover crop increased N₂O emissions compared with oats and a control without a cover crop. In those early stages, conditions for high N₂O flux occurrence were promoted by the use of cover crops, as they increased soil moisture and, when vetch was the cover crop, nitrate content. Although the oats+vetch mixture reduced soil nitrate availability compared with vetch, this was not reflected lower N₂O emissions. The use of oats as a cover crop did reduce N₂O emissions compared with vetch and also decreased maize yields by 30.6%. The low-rate N fertilization in treatments that included vetch as a cover crop did not increase N₂O emissions or yield significantly. Our study demonstrates that in low-input cropping systems under no-tillage, the use of legume cover crops can favor yields and also increase N₂O emissions during the early stages of the following cash crop. Consequently, future work should explore mitigation strategies during this period.