Nitroxin improves yield and phenol compound of purple coneflower (Echinaceae purpurea L.) root under different irrigation regimes

Purple coneflower (Echinaceae purpurea (L.) Munch) root is a rich source of phenolic components used in pharmaceutical industries and the content of phenolic components depends on many factors such as drought stress and nitrogen (N) nutrition. This experiment was conducted in Lordegan, Iran, from 2014 to 2016, to investigate the effect of N and nitroxin on the content of phosphorus, potassium and nitrate, yield, content and yield of phenol compound of purple coneflower root under three irrigation regimes. Irrigation after 25%, 50% and 75% of soil water depletion, as the main factor and 0 kg N ha-1 (control), nitroxin (containing Azotobacter and Azospirillium bacteria), 40 kg N ha-1, a combination of nitroxin and 40 kg N ha-1 and 80 kg N ha-1 were considered as the sub-factor and arranged as a split plot in the randomized complete block design with three replications. Nitrogen application increased potassium content and root yield and also phosphorus content in all irrigation levels. The highest root nitrate accumulation was obtained by the application of 80 kg N ha-1 in all irrigation treatments. Irrigation after 75% of soil water depletion decreased potassium content and root yield. The highest root yield was achieved from nitroxin+40 kg N ha-1. Root phenolic compounds were raised by increasing irrigation intervals, and N consumption decreased them at each irrigation regime. The highest phenolic compound yield was obtained from the application of nitroxin in irrigation after 75% of soil water depletion. Generally, irrigation after 75% of soil water depletion and utilization of nitroxin is suggested for the best quantity and also quality root production in the studied region.