Introduction: Quinoa (Chenopodium quinoa Willd.) is one of the most nutritious plants which can play an important role in human and livestock nutrition due to its unique nutritional properties. Quinoa grain is an excellent source of mineral elements such as manganese, iron, potassium, copper, zinc and phosphorus, and contains group B vitamins such as riboflavin, thiamin and niacin. Determining the optimal planting density is one of the most important effete factors to achieving optimal plant performance. Since the availability of resources needed by the plant such as light, water and nutrients is closely related to the density of plants, therefore it is very important to adjust the density of cultivation in order for the plant to optimally use the resources it needs for growth and development.
Materials and Methods: This research was carried out in order to investigate the planting density on the morphological traits, yield and yield components as well as the qualitative characteristics of quinoa grain in 2022 year as a randomized complete block design with three replications in the research farm of Department of Agricultural Science, Faculty of Bahonar, Technical and Vocational University (TVU) in province of Tehran. The experimental treatments include five different plant distances (10, 20, 30, 40 and 50 cm) on fixed rows (50 cm) (10×50, 20×50, 30×50, 40×50, 50×50). Due to drip irrigation tape, the distance between the rows was fixed and 50 cm, but the distance between the plants in the cultivation rows was variable (10, 20, 30, 40 and 50 cm).
After the land was prepared, the seeds were sown in heaps (5-7 seeds) at the desired intervals and immediately irrigated as drops. Irrigation intervals were done once every five days. After the seedlings reached the stage of 4-7 leaves (height about 10-15 cm), thinning was done. In the flowering stage, two plants were taken from each plot and after separating the leaves, the leaf area was measured with the help of a scanner model leaf area meter and calculated with the help of Image J program.
The grain nitrogen percentage was measured by the Kjeldahl method. Crude protein was also calculated by multiplying nitrogen percentage by 6.25 (AOAC, 2005). The amount of grain phosphorus was measured by colorimetric method (Molybdate-vanadate), grain potassium was also measured with the help of a flame photometer, and grain starch was also measured according to the method (Hedge et al., 1962). Analysis of data variance was done by SAS software (version 9.1), data comparisons were done using Duncan's multi-range test at the five percent probability level, and graphs were drawn with Excel software (2016 version).
Results and Discussion: All investigated traits were influenced by the spacing of the plants in the row. The highest plant height was observed in the treatment of 10 and 50 cm between the plants. The highest index of leaf area (903.5 square centimeters per plant), the number of side branches (18), and the length of the main cluster (37.3 cm) were observed in the 50 × 50 planting distance. The low weight of 1000 grain (2.05 g) and harvest index (28.5%) were observed in 50 × 10 treatment. The lowest and highest seed yields were obtained with 348.3 and 394 grams per square meter, respectively, in the spacing of 50 × 10 and 50 × 50, respectively. The highest percentage of seed protein and starch was observed by 19.1% and 71.6%, respectively, at the maximum distance between the plants (50 cm). The content of phosphorus and potassium of seeds (395.4 and 897.9 mg/g dry weight of grain) were also obtained at a distance of 50 cm between plants.
Conclusion: In general, according to the results obtained in the current research and the similarity of many traits measured between the 50 × 50 and 50 × 40 cm cultivation distances, it is suggested that under drip irrigation conditions with tape, the planting distance should be 50 × 40 cm.