Qualitative attributes, nutritional traits and yield components of Calendula officinalis L.: response to liquid NPK fertilizer, humic acid, and moringa leaf extract

Calendula officinalis L. is an economic annual or biennial herbaceous medicinal plant which is widely cultivated in the world due to its medicinal and ornamental assets of flowers. In order to improve flower yield and quality, a two-sectional factorial experiment (CRD, r = 3) was conducted in Mosul, Iraq, in 2023. The plants were exposed to different fertilization: Factor A; NPK Liquid Fertilizer (0:33:42) (1.5- and 3-mL L^-1) and Factor B; Moringa leaf extract at 0-, 2-, and 4-mL L^-1 (section a) and in section b were exposed to 0, 1.5, and 3 g L^-1 Humic acid and Moringa leaf extract at 0-, 2-, and 4-mL L^-1. The liquied NPK fertilizer (CF), Moringa extract (ME) and Humic acid (HA), as well as their interactions, significantly improved vegetative growth, flowering and phytochemical properties of flowers. In section a, the highest plant height (16.66 cm) was obtained with application of 3 mL L^-1 liquied NPK fertilizer without extract, branch number (13.33) with 3 mL L^-1 CF + 4 mL L^-1 ME, SPAD (43.54 value) 3 mL L^-1 CF + 2 ml L^-1 ME, flower diameter (73.75 mm) 3 mL L^-1 CF + 0 mL L^-1 ME, fresh flower weight (270 g) 3 mL L^-1 CF + 2 mL L^-1 ME, flower dry weight (100 g) 1.5 mL L^-1 CF + 4 mL L^-1 ME, carotene content (0.86%) 1.5 mL L^-1 CF + 4 mL L^-1 ME and 3 mL L^-1 CF + 2 mL L^-1 ME, phosphorus (0.359%) and potassium (1.39%), and nitrogen content (2.47%) in 3 mL L^-1 CF + 4 mL L^-1 ME. In second experiment (b), the responses of different traits to treatments were less diverse, so that the combined application of 3 g L^-1 humic acid and 2- or 4-mL L^-1 moringa extract consistently produced the greatest improvements across vegetative, reproductive, and biochemical traits, demonstrating a strong synergistic effect on the growth and quality of C. officinalis. Furthermore, the PCA results demonstrated the superior performance of Humic acid 3 g L^-1 × Moringa extract 2 mL L^-1, highlighting the importance of combining higher humic acid levels with moderate Moringa extract concentrations to maximize nutrient assimilation, vegetative growth, and reproductive output. Furthermore, the HPLC analysis indicated that the synergistic application of liquied NPK fertilizer or humic acid with 4 mL L^-1 of Moringa extract promotes the biosynthesis of key phenolic metabolites in C. officinalis.