Plant density and nitrogen fertilizer effects on yield and qualitative characteristics of marigold (Calendula officinalis L.) under Torbat-e-Jam climatic conditions

Marigold (Calendula officinalis L.) is one of the oldest medicinal plants which had been used for the pharmaceutical industries. In order to evaluate the effects of different plant densities and nitrogen levels on growth, yield and qualitative characteristics of marigold flower, a field experiment was conducted as split plot based on a randomized complete blocks design with four replications at the Agricultural Research Station, Azad University of Torbat-e-Jam, during growing season of 2008-2009. Main and sub plots included four nitrogen levels (zero, 30, 60 and 90 kg.ha-1) and three plant densities (25, 50 and 75 plants.m-2), respectively. Nitrogen (as Urea) was used at 4-6 leaves and flowering stages of marigold as topping dress. Plant height, shoot and root dry weights, seed yield, flower yield, biological yield, harvest index (based on the flower yield), essential oil content and flower extract contents of marigold were studied. The results showed that the simple effects of nitrogen and plant densities were significant (P≥0.01) on plant height, shoot and root dry weights, seed, flower and biological yields, harvest index and essential oil and extract contents of marigold. By increasing nitrogen level from zero to 60 kg.ha-1, enhanced flower dry weight and essential oil content due to increasing in vegetative growth and photosynthesis up to 100% and by increasing nitrogen level up to 90 kg.ha-1, these traits declined 33 and 52%, respectively. Whereas, by increasing plant density from 25 to 50 plants.m-2, increased flower yield and essential oil content up to 23 and 29% and by increasing in nitrogen level up to 75 plants.m-2, these trait decreased 20 and 44%, respectively. Thus, in order to achieve suitable quantitative and qualitative yields of marigold can be considered as appropriate levels of nitrogen fertilizer and crop density as these agronomic approaches.