Effect of sowing date and rate on the yield and flavonolignan content of the fruits of milk thistle (Silybum marianum L. Gaertn.) grown on light soil in a moderate climate

In the moderate climate of Poland it is recommended that milk thistle (Silybum marianum L Gaertn.) be grown on fertile soils. The plant, however, develops a strong root system, so a working hypothesis has developed that cultivation can be extended to light soils with periodic water deficits. The aim of the present research was to determine the effects of sowing milk thistle on light soil at different dates and rates on the achene yield and flavonolignan content. This experiment was carried out during 2004-2006 at the Mochelek Experiment Station of the University of Technology and Life Sciences in Bydgoszcz (53 degrees 13' N; 17 degrees 51' E). The average fruit yields were 1.23 t ha(-1); those of silymarin were 26.5 kg ha(-1). The moisture and thermal conditions during the research years caused the fruit yields to range from 0.55 to 1.68 t ha(-1) and silymarin yields from 13.3 to 35.4 kg ha(-1). Delaying sowing from early to mid-April increased the plant density and decreased numbers of inflorescences and fruits per inflorescence; as a result, no effect of sowing date on fruit yield was found. Delaying the sowing date increased silymarin content by about 0.4% and its yield by 5.3 kg ha(-1). Increasing the sowing rate from 12 to 24 kg ha(-1) resulted in a slight (40 kg ha(-1)) but significant increase in achene yield; however, it did not affect the silymarin content. The average silymarin content in fruits was 2.18%. The ratio of silydianin to silychristin was 1:2.2, and the ratio of silydianin to the sum of silybinin and isosilybinin was 1:3.3. (C) 2010 Elsevier B.V. All rights reserved.