Yield and silymarin content in milk thistle (Silybum marianum (L.) Gaertn.) fruits affected by the nitrogen fertilizers

Abstract

Milk thistle (Silybum marianum (L.) Gaertn.) is a common weed that has been introduced as a medicinal plant for silymarin production. This renders it important to optimize cultivation techniques, including fertilization. In the present study, a two-year field experiment was conducted to evaluate the influence of conventional and stabilized nitrogen fertilizers on plant growth, fruit yield, and fruit quality. The experiment was conducted in a randomized complete block design with five fertilization treatments (control, conventional nitrogen fertilizer applied at 75 kg/ha and 125 kg/ha, and stabilized nitrogen fertilizer applied at 75 kg/ha and 125 kg/ha. Nitrogen fertilization had a significant effect on vegetative and yield parameters. Specifically, the application of nitrogen fertilizers positively influenced rosette diameter, height, aboveground dry biomass, total chlorophyll content, number of capitula per plant, number of fruits per central capitulum, and fruit yield. In particular, in most traits, the usage of high nitrogen levels of the two types of fertilizer had the most pronounced impact. The application of the stabilized fertilizer at a rate of 125 kg N/ha induced an increase in fruit yield of up to 29.6 %. Nitrogen fertilization had no impact on the accumulation of oil and silymarin in the fruits, although some effects on oil and silymarin yield were noted. In general, the application of nitrogen fertilizers had no effect on the antioxidant activity or total phenolic content of the fruit extracts. Finally, climatic conditions affected the growth and productivity of milk thistle, as fruit yield was favoured by wet conditions.