Nutrient deficiency affects growth, flower quality and yield of American marigold (Tagetes erecta)

American marigold or Mexican marigold (Tagetes erecta L.) is considered an important economic flower crop in Thailand, covering approximately 1,000 ha of cut flower production area. Although there are quite a number of breeding companies supplying adequate good seeds for the growers, the problems affecting flower production appear to occur from the growers themselves. Lack of understanding on fertilizer management leads to poor quality of flowers and yield. However, the information on deficiency symptom of this plant is limited. Therefore, this experiment was conducted to reveal visible deficiency symptoms related to insufficient essential elements supplies that marigold plants get from the soil or planting materials. Informative knowledge extracting from the results of this study could certainly help the growers to understand fertilizer requirement of the marigold plants they are growing. The main objective of the experiment was to determine visible element deficiency symptoms including growth, yield and flower quality of marigold plants grown in different fertilizer conditions. The experiment was carried out under the glasshouse environment with the temperature being 25-30°C and 80-85% relative humidity. Marigold seeds were germinated for 3 weeks prior to transplanting into hydroponic system using double pots technique. The experimental design of nutrient applications used was completely randomized design (CRD) with 14 treatments (14 Ts), each treatment contained 3 replications of 1 experimental plant replication^‑1. In T1, the plants were supplied with only deionized water and in T2, the plants were given all essential elements referring to Hoagland solution as control treatment. The rest of the treatments, from T3 to T14, the solutions were deficient of N (T3), P (T4), K (T5), Ca (T6), Mg (T7), S (T8), Fe (T9), B (T10), Mn (T11), Zn (T12), Cu (T13) or Mo (T14), respectively. Recordings were done on plant height, root length, leaf color intensity, leaf area, flower quality and total flower fresh weight (FW). The result showed that at 6 weeks of nutrient applications, the lowest plant height was observed in the plants grown in deionized water. The plants in -K and -P treatments gave lower plant height than those in control treatment. Yellow leaves were detected in the treatments lacking N, Mg, Fe and Mo with decreased leaf color intensity. Reduced root length was found in Ca-deficit plants. Stems of B-deficit plants appeared brittled broken while the leaves curled, thickened and wrinkled. All deficiency treatments except those of Cu, Mo and Mn delivered reduced total leaf area and total flower fresh weight.