Effect of Sulfuric Acid, Humic Acid and Potassium Nitrate Foliar Spraying on Petal Color Quality, Antioxidant Activity, Carotenoids and Flower Yield in Marigold (Calendula officinalis L.)

In order to investigate the effects of sulfuric acid, humic acid and potassium nitrate foliar spraying on quantitative and qualitative of marigold a field trial was conducted in Ramin Agriculture and Natural Resources University of Khuzestan, Iran in 2015-2016. This study was carried out using a split factorial experiment in a randomized complete block design with four replications. Treatments included potassium nitrate (N1=no application, N2=250 ppm and N3= 500 ppm) as the main factor, sulfuric acid (S1=no application and S2=5 L/ha) and humic acid (H1=no application and H2=16 kg/ha) as the second factor. Studied traits included capitol diameter, number of ray flowers in inflorescences, total number of inflorescences per m2, fresh and dry weight of inflorescences, harvest index, petal carotenoid concentrations, antioxidant activity and petal color quality (L*a*b parameters). The highest inflorescence dry weight (53 g m-2), fresh and dry weight of inflorescences (380 g m-2), total number of inflorescences per m2 (372), number of ray flowers in inflorescences (58) and harvest index (14%) were detected in N2S1, N2S2, N2S2, N2S1 and N1H2, respectively. The least antioxidant activity (0.048 mg ml-1) was obtained in S1H2. The highest a (5.23) and L (61.64) color parameters for yellow flowers and b (84.44) color parameter for orange flowers were found in N1S1H1, N3S2H2 and N2H2, respectively. In general, the best treatments for the two important traits of inflorescence dry matter yield and number of inflorescences per square meter were N2S1 and N2S2, respectively.