Effect of planting date and density on dry matter and antioxidant capacity of purple coneflower [Echinacea purpurea (L.) Moench] root

To find out the effect of planting date and planting density on antioxidant capacity, phenolic compounds, yield dry matter and characteristics of medicinal plant purple coneflower root, a randomized complete block design in split plot arrangement with three replications was conducted in Research Farm of Sari Agricultural Sciences and Natural Resources University in 2012-2013. Experimental treatments included three planting dates (April 9, May 9 and June 8 2013) and three planting density (7, 10 and 16 plant/m2). Measurements were performed in full bloom stage. Results of experiment showed a significant increment of penetration depth of root in 9 may with a density of 16 plant/m2. The highest root volume and dry matter were related to 8 June and 7 plant/m2. However, the highest total dry matter (130.5 g/plant) was related to the purple conflowers that planted on 9 April with 10 plant/m2. Plants grown on 8 June with a density of 7 plant/m2 resulted to the highest ratio of dry matter root to total and root to shoot. The highest cichoric acid (19.5 mg/ g dry matter) and total phenol (30.8 mg of GAE/ g dry matter) content of root were observed in plants grown in 9 May with a density of 16 plant/m2. The highest amount of total flavoneid and antioxidant capacity of root were measured in coneflower plants that planed in 8 June with a density of 16 plant/m2. In conclusion, it seems that late planting date 8 June in this experiment conditions is suitable for more root dry matter, total flavoneid and antioxidant capacity, while planting date 9 May is suitable for more cichoric acid and phenollic content in the root of the coneflower plants. In addition to, low density of 7 plant/m2 resulted in increase in root dry matter and decrease in cichoric acid and total phenol content as well as antioxidant capacity in coneflower roots.