Changes in seed and oil yield of Calendula officinalis L. as affected by different levels of nitrogen and plant density

In order to study the effect of different levels of nitrogen and plant density on seed and oil yield of calendula (Calendula officinalis L.), an experiment was conducted at research field of Faculty of Agriculture, Lorestan University, Khorramabad in 2009. The experiment was carried out as a split-plot arrangement based on a randomized complete block design with three replications. Nitrogen level was the main factor with four levels (0, 50, 100 and 150 kg/ha) and plant density was the sub-factor with three levels (50, 33 and 25 plants/m(2)). Number of heads/plant, number of seeds/plant, 1000-seed weight, weight of seeds/plant, seed yield, oil content and oil yield were recorded. Results of analysis of variance (ANOVA) showed that nitrogen levels had no significant effect on different parameters (P>0.05). However, Duncan's Multiple Range Test showed a significant difference among means in all parameters (P<0.05). Application of 100 kg/ha nitrogen showed the highest seed and oil yield with 118.919 and 18.152 g/m(2), respectively. Moreover, ANOVA showed that plant density had a very significant effect on number of heads/plant, number of seeds/plant and weight of seeds/plant (P<0.01). According to the results, as plant density decreased, number of heads/plant, number of seeds/plant and weight of seeds/plant increased. ANOVA also showed significant effect of the interaction between nitrogen levels and plant densities on weight of seeds/plant, seed and oil yield (P<0.05). The highest seed and oil yield (124.472 and 19.564 g/m(2), respectively) was found with application of 100 kg/ha nitrogen and 25 plants/m(2) which were not significantly different from those with application of 150 kg/ha nitrogen and 33 plants/m(2). Considering the importance of less application of chemical fertilizer in agriculture, 100 kg/ha nitrogen and 25 plants/m(2) could be recommended for producing desirable seed and oil yield in calendula under Khorramabad (Iran) climatic conditions.