The effect of sowing date and planting density on grain yield and some nutritional quality characteristics of three seed-quinoa genotypes

Quinoa (Chenopodium quinoa Willd) is a plant with high nutritional value and has good adaptability to different growing conditions. To investigate the effects of planting date and density on the seed quality of three quinoa genotypes (Q29, Titicaca, and Red Carina), a field experiment was conducted in 2019-2020 at the research field of Agriculture and Natural Resources Campus, Razi University, Kermanshah, Iran. The seeds were sown on three dates (15th March, 15th April, and 15th May) under two planting densities (40 and 60 plants/m2). The experiment was conducted as a split-plot factorial design based on the randomized complete block design with three replications. The results revealed that both sowing date and plant density influenced the nutritional composition of the quinoa genotypes. The grain yield varied between 1642 and 2351 kg/ha, and the amino acids profile varied according to planting date and planting density. The amino acids histidine, glutamic acid, leucine, and lysine increased with delaying sowing date whereas threonine, tyrosine, arginine, methionine, glycine, proline, isoleucine, valine, serine, alanine, aspartic acid, asparagine, cysteine, phenylalanine, and glutamine decreased with delaying the sowing date from 15 March to 15 May. The Titicaca genotype produced maximum grain yield under the third sowing date while in the case of the first sowing date, all studied genotypes were more responsive regarding most amino acids. Also, the most suitable plant density to result in the highest grain yield was 60 plants/m2. The mineral content of the quinoa seeds was not influenced significantly by the sowing date, plant density, genotype, and their interactions, except for calcium which was affected significantly by the genotype. The lowest saponin content was observed in Titicaca under the planting density of 40 plants/m2. These results indicated that both sowing dates and plant densities influence the nutritional composition of quinoa genotypes.