Pot marigold (Calendula officinalis L.) is an annual medicinal plant which has been cultivated for herbal raw material (flower heads); its material has been benefiting the pharmaceutical and cosmetic industry since the ancient times. A field study was carried out in the years 2006-2007 in the Experimental Farm of the Islamic Azad University of Takestan in Iran. The study was conducted on a fine, mixed, thermic, and Typic Haplocambids soil with the granulometric composition of sandy-loam. The aim of the experiment was to determine the effect of different nitrogen rates (N0 = 0, N1 = 30, N2 = 60, N3 = 90 kg ha-1) and irrigation regimes (I1– irrigation after 40 mm, I2– irrigation after 80 mm, and I3– irrigation after 120 mm evaporation from class A pan) on some agronomic features of flower heads as well as on yield and quality of marigold raw material. Water deficit stress caused reduction in petal yield, extract yield, petal/flower weight ratio, and flower quality while it did not affect flavonoid content significantly. Extract content increased with increasing irrigation intervals based on 80 mm evaporation from class A pan. Extract yield of pot marigold was the lowest (112.8 kg ha-1) in the control treatment (without nitrogen) and the highest (133.7 kg ha-1) in the plots where nitrogen fertilization applied at the maximum rate (90 kg ha-1). It was understood that the application of 30 kg N ha-1to increased extract content drastically as compared to N2 and N3 treatments. Petal/flower weight ratio and flower quality did not differ markedly for fertilization rates from 0-90 kg N ha-1. The highest flavonoid content (1.59%) was achieved from plots which utilized a combination of I2×N1 treatment. However, the maximum petal yield was related to application of 90 kg N ha-1 and a normal irrigation (I1).
