Abstract
Calendula (Calendula officinalis L.) is an annual winter plant that belongs to family Asteraceae. It generally used as landscape bedding or ornamental potted plants. The economic and environmental sustainability of ornamental plants production can be improved by environmentally friendly organic substance, such as humic acid (HA). Seedlings of Calendula were sprayed by the organic foliar (HA) fertilizer (0.0, 0.5, 1.0, 1.5, and 2.0 g/L) for one, two, three and four times every 15 days after transplanting. Growth traits, leaf pigment contents, leaf gas exchange, and leaf water potential of C. officinalis were determined. The results showed that plants treated with foliar applications of HA with different levels exhibited plant height, the number of leaves, leaf area, shoot dry mass, and as well as the number of flowers, flowers display time, flower diameter and flower dry mass. shootsThe promoting influences of the foliar application of HA on the growth and development of plants were obvious reflected using the two dose 1.5 and 2.0 g/L at three times. Humic acid enhanced vegetative and flowering traits of the Calendula plant, improved leaf pigments content and both photosynthesis rate and transpiration rate. Therefore, HA gives a good chance to improve the growth of Calendula as a model for ornamental plants production.
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