<p>Understanding the impact of environmental conditions on crop performance is essential for sustainable agriculture, especially in regions like the Mediterranean, which is facing more frequent droughts and heatwaves due to climate change. This study demonstrates for the first time the significant impact of adverse field environmental conditions, particularly scarce precipitation combined with elevated temperatures, on biomass yield, nutritional composition, and nutrient utilization efficiency of triticale and oat forage crops under rainfed conditions in the Mediterranean region. This study evaluated the agronomic performance and nutritional quality of oat and triticale forage across two seasons (2017/18 and 2018/19) and harvest dates (April and May) under rainfed conditions in Southern Europe. Both species produced similar biomass yields, but yields declined in the second season due to reduced rainfall and elevated temperatures. The environmental conditions, genotype, and harvest date significantly influenced forage quality and nutrient utilization efficiency. While drought stress is commonly associated with reduced nutrient concentrations, this study found increased crude protein levels under water-limiting and high-temperature conditions. Nutrient utilization efficiency for phosphorus (P) and potassium (K) increased, while nitrogen (N) efficiency decreased, with no significant changes in calcium (Ca) and magnesium (Mg). Genotype and harvest date also affected nutrient use efficiency. The results highlight the importance of understanding plant responses to environmental stressors to predict the impacts of climate change on food production. Further research is needed to develop strategies for maintaining sustainable food supplies in a changing climate.</p>