Plant-plant interactions could shift from facilitation to competition or vice versa depending on stress conditions. Many researchers are investigating these interactions among the plant species but knowledge about the effect of these interactions on the establishment and growth is limited. Therefore, the effect of plant-plant interactions on forage yield and quality were investigated in pea-cereal mixtures under Central Anatolia conditions during the 2018 and 2019 years. Forage pea were sown using different densities (80, 100, 120 plants m(-2)) and as binary mixtures with 50-75 % reduced seeding ratio of oat, silage maize, and Sudangrass as a mixture. The highest dry matter yield was 7224.7 kg ha(-1) and, obtained from 50 % reduced silage maize + 100 plants m(-2) forage pea mixture. All mixtures increased dry matter yield but decreased the crude protein content concerning forage pea monoculture. Sudangrass mixtures negatively affect the crude protein content in the mixture and decreased it down to 14.58 % but it was, nevertheless, considerably high. Forage NDF and ADF contents were generally higher in Sudangrass mixtures. Above- and below-ground relative neighbor effects (ARNE and BRNE respectively) were facilitative under stressful climate conditions of 2018 but they shifted into competition in 2019. The cereals used in the mixtures caused a competitive effect on forage pea in terms of BRNE. The results indicated that plant-plant interactions could significantly affect the forage yield, quality, and competition. Forage pea (100 plants m(-2)) could be cultivated as a second crop when sown as a binary mixture using 50% reduced silage maize (5000 plants m(-2)).