Seed yield response to N fertilization and potential of proximal sensing in Italian ryegrass seed crops

•Maximum seed yield in Italian ryegrass was reached at a total available N of 141kgNha−1.•N fertilization rates higher than 90kgNha−1 resulted in higher N uptake, but not in higher seed yields.•Remedial N fertilizations in the 2–3 node stage can secure seed yield in N efficient crops.•NNI values of 0.83, 0.72 and 0.59 BBCH 32–33, 51 and 61 allowed maximum seed yield.•NDVI values were heavily dependent on the trial year, which compromises their usefulness.