The Effect of Sowing Date and Harvest Time on Leafy Greens of Quinoa (Chenopodium quinoa Willd.) Yield and Selected Nutritional Parameters

In 2015–2017, field experiments were conducted, in two facilities of the Wroclaw University of Environmental and Life Sciences: at the Research and Didactic Station in Psary (51°19′08” N, 17°03′37” E) and in the plots of the Department of Crop Production in Pawlowice (51°17′32” N, 17°11′72” E). The research aimed to evaluate fresh biomass yield and selected quality parameters of quinoa grown as a green leafy vegetable. The study was conducted on two soils: medium (clay soil texture) and light (sand soil texture), sowing quinoa in spring and summer periods. On both soils, quinoa was harvested 5 times at each sowing date. The yields of fresh plant biomass, basic morphological characteristics and certain quality traits were compared. All experimental factors had a significant effect on quinoa fresh biomass yield. On light soil, quinoa yielded 4 times lower than on medium soil, and its cultivation posed a high risk, especially at the summer sowing date. The experimental factors used had the greatest effect on macronutrient content. Growing quinoa on medium soil yielded biomass with higher K, Mg, Ca and N-NO3 concentration, while spring sown plants had higher K and N-NO3 concentration. Harvesting date had the greatest effect on the change in nutritional values. Potassium content decreased as the harvest date was delayed, and N-NO3 content decreased gradually until the fourth harvest date. The results showed that quinoa should be harvested as a green leafy vegetable when it reaches a height of 20–30 cm; biomass production is then at 500–1000 g per m2, potassium content is less than 10 g per 100 g dry matter and N-NO3 content is less than 100 mg 100−1 f.m.