Nitrogen (N) fertilization is well studied for black oat (Avena strigosa Schreb.), but the crop response to gypsum and the combination of both is underexplored, especially in long-term studies under no-till. Topdressing N rates (0, 50, and 100 kg ha(-1)) were applied for black oat over 2017 and 2018 crop seasons in a gypsum experiment (0, 3, 6, 9, and 12 Mg ha(-1)) started in 2009. Soil chemical attributes, forage yield, macronutrients content, and apparent N recovery efficiency (RE) were evaluated. Gypsum increased Ca2+ and SO42- in the soil and in the forage, while Mg2+ was decreased in the soil. N decreased in the soil but increased in the forage with gypsum, probably due to greater root growth and absorption potential, what also explains higher P and K in the forage. N-fertilization increased all macronutrients in the forage. The RE was higher with 50 kg([N]) ha(-1) than with 100 kg([N]) ha(-1), while residual gypsum rates had minimal or no effect. Forage yield was higher with 3 Mg ha(-1) (2017) and up to 6 Mg ha(-1) (2018) of gypsum rates in the absense of N-fertilization. The long-term effect of 6 and 9 Mg ha(-1) of gypsum presented higher yields with 50 and 100 kg([N]) ha(-1) which were mostly equivalent. Without gypsum, the yield was higher with 100 kg([N]) ha(-1). Our hypothesis was not confirmed, and no synergistic effect was observed in forage yield and RE by black oat in response to the long-term effect of gypsum associated with N-fertilization.