Optimizing manganese and iron delivery for contrasting cultivars of subirrigated greenhouse-grown pot chrysanthemums

Excessive fertilizer use in greenhouse floricultural operations results in low-nutrient use efficiency by plants and poses environmental risk. Here, we optimized the usage of fertilizer manganese (Mn) and iron (Fe) by modern cultivars of subirrigated pot chrysanthemum. Mn and Fe (approximately 100% to 6% of industry standards) were provided in an otherwise balanced nutrient solution during vegetative growth, and all nutrients were removed during reproductive growth. Two experiments were conducted for each nutrient in a naturally lit research greenhouse using a split-plot design with four blocks arranged randomly. Mn (5.00–0.3125 µmol L−1) or Fe (10.56–0.66 µmol L−1) was the main plot and cultivar (“Milton Dark Pink”, “Williamsburg Purple”, and “Olympia White”) was the subplot. The cultivars exhibited contrasting phenotypes. However, any treatment effects on plant yield and inflorescence development and quality were minor, so that Mn or Fe use efficiency increased approximately 16-fold with decreasing supply. Even though leaf Mn, zinc, and calcium levels were occasionally correlated inversely with decreasing Fe delivery, the leaf Mn (44.8–121.8 mg kg−1) and Fe (68.5–121.8 mg kg−1) levels were always considered acceptable. These findings contribute to the development of a low-input practice that would improve the sustainability of floricultural crop production.