Abstract:Background and aims: The concepts of critical nitrogen (N) concentration and nitrogen nutrition index (NNI) provide effective tools for assessing the N nutritional status of pastoral systems. However, no conclusive data exist concerning the effects of stubble height at harvest on the Ndilution curve [N concentration (N%) = a(biomass)?b] and mixed species cultivation on N nutritional status of forage plants with contrasting growth strategies. To evaluate these effects, three cool-season perennial grasses (exploitative, Arrhenatherum elatius L.; moderately exploitative, Dactylis glomerata L.; conservative, Festuca arundinacea Scherb.) were grown under different cultivation methods either as pure stands or as a mixture and conducted two experiments.