Introduction
Quinoa (Chenopodium quinoa Willd) is an annual plant of the legume family, native to Latin America. In addition to its high nutritional value, this plant has a remarkable ability to tolerate a variety of abiotic stresses, including drought, salinity, and cold, as well as to grow on marginal lands. Due to its relative tolerance to drought and salinity stresses, extensive genetic diversity, and ability to adapt to different climatic conditions and high water use efficiency, it is considered a suitable plant for the exploitation of limited water resources and saline soils. In terms of nutritional value, quinoa seeds, the main product of this plant, contain between 14 and 20% protein and are rich sources of essential amino acids such as lysine and methionine, substances that are found in low amounts in most cereals.

Materials and Methods
In order to investigate the effect of different plant densities and cultivars of quinoa on growth, physiology and forage yield, a field experiment was conducted as a factorial experiment in a randomized complete block design with four replications in the fall and winter of the 2023-2024 crop year at the research farm of Agricultural Sciences and Natural Resources University of Khuzestan. Experimental factors included plant density at three levels (30, 50 and 70 plants m^-2) and quinoa cultivars (Rahmat and Sadooq). The evaluated traits were chlorophyll a, b, carotenoid, spad number, leaf area index, forage protein percentage, forage protein yield and forage yield.

Results and Discussion
In this study, neither planting density nor cultivar had a significant effect on chlorophyll a, chlorophyll b, carotenoid content, or SPAD values. However, analysis of variance showed that planting density significantly affected leaf area index, forage protein concentration, and forage protein yield, whereas cultivar significantly affected forage protein yield and dry forage yield. In addition, the interaction between planting density and cultivar had a significant effect on forage protein concentration and forage protein yield. The results showed that the highest and lowest of leaf area index with an average of (3.87) and (3.11) were observed in the density treatment of 70 and 30 plants per square meter, respectively. Also, the highest percentage of forage protein (6.35 and 6.03 percent, respectively) was observed in the density of 30 plants per square meter and the lowest were (4.10 and 4.88 percent, respectively) in the density of 70 plants per square meter in two varieties of Sadooq and Rahmat. The highest forage protein yield (1163 kg ha^-1) was observed at densities of 30 plants per square meter, in Sadooq cultivar and the lowest (540 kg ha^-1) was obtained at densities of 70 plants per square meter, in Rahmat cultivar. Also, the highest dry forage yield with an average of 18259 kg ha^-1 was observed in the Sadooq cultivar and the lowest dry forage yield with an average of 10633 kg ha^-1 was observed in the Rahmat cultivar. Therefore, the significant difference between the two studied cultivars were present.

Conclusion
Increasing plant density to the optimum level, without creating intense intraspecific competition, by making optimal use of environmental resources such as light, water, and nutrients, improved leaf area index and increased forage yield in quinoa. The results showed that choosing the right cultivar plays an important role in forage yield, especially through its effect on maturity time and weed resistance. Significant differences in forage yield were observed among the evaluated cultivars, with Sadooq producing the highest forage yield. These findings indicate that selecting an appropriate cultivar in combination with an optimal planting density can be an effective strategy for improving quinoa forage production.