Effects of nitrogen application and plant densities on flower yield, essential oils, and radiation use efficiency of Marigold (Calendula officinalis L.)

Efficient use of radiation for medicinal plants production، might increase flower yield، essential oils and extract yield. A split plot design. was used in a two years (2005 and 2006) field study in Torogh region (36،10° N،59. 33° E and 1300 m altitude) of Mashhad، Iran، to observe the effects of different nitrogen application and plants densities on flower dry matter production، essential oils، and radiation use efficiency in a multi-harvested Marigold (Calendula officinalis). The levels of nitrogen fertilizer were 0، 50، 100 and 150 kg ha-1 and levels of density were 20، 40، 60 and 80 plant m-2. The combined analysis results revealed significant effects of nitrogen and density levels on flower dry matter production، essential oils، and radiation use efficiency of Marigold. The highest dry flower production obtained by 150 kg ha-1 N and 80 plant m-2 plant population (102. 86 g m-2). The higher flower dry matter production caused more essential oils and extract production in high nitrogen and density levels. The amount of essential oils and extract per 100g flower dry matter decreased during the flower harvesting period. The higher amount of essential oil and extract obtained at early flowering season. The essential oil and extract ranged from 0. 22 to 0. 12 (ml. per 100g flower dry matter) and 2. 74 to 2. 13 (g per 100g flower dry matter) respectively. Increase of both nitrogen and density caused higher radiation use efficiency. The most radiation use efficiency obtained at 150 kg ha-1 nitrogen and 80 Plant m-2desity treatments. In 150 kg ha-1 nitrogen treatment، increase of density levels from 20 plant m-2 to 80 Plant m-2 caused increase in radiation use efficiency from 1. 41 g MJ-1 to 1. 44 g MJ-1 respectively.