Effect of nitrogen fertilization and plant density on seed yield and fat content and quality of pot marigold (Calendula officinalis L.) under climatic conditions of Belarus

This paper presents the results of a study on the effect of different N fertilization and seeding rates on yield and some quality parameters (of seeds) of pot marigold. A field experiment was carried out during 2014–2016 under soil and climatic conditions of Belarus (Priluki Research Station near Minsk). The experiment included the following factors: N fertilization rate 40, 60, 80, 100 kg hm⁻¹; plant density per 1 m² (30, 50, 70, 90). The experiment was set up as a randomized block design in five replicates, with a single plot area of 8.0 m² . The soil in Priluki was characterized by medium nutrient availability (at the level: P = 120–127, K = 164–174, Mg = 59–66 mg kg⁻¹ soil). Regardless of the experimental factors, weather conditions had a significant impact on pot marigold productivity. The year 2016, characterized by an even distribution of rainfall during the growing season and moderate air temperatures, proved to be most beneficial for pot marigold productivity and quality. Hydrological conditions in the other years (2014 and 2015) there was a slight drought. The year 2014 should be considered to be cold, whereas the second year of the study (2015) was moderately warm. Best production effects (seed yield, fat yield) were obtained at rates of 60–80 kg N hm⁻¹. This rate of nitrogen fertilization also modified the fatty acid composition, contributing to a higher content of linoleic acid and calendic acid (∑ α-calendic and β-calendic acids). A nitrogen rate of 100 kg N hm⁻¹ proved to be irrational in terms of the quantity and quality of pot marigold yield. A density of 50–70 plants per 1 m² resulted in the highest seed and fat yield per unit area. A plant density of 50 plants per 1 m² resulted in the highest content of C18 unsaturated acids (stearic acid, oleic acid, linoleic acid) in the oil