Physio-morphological and biochemical responses of pot marigold ( Calendula officinalis L.) to split iron nutrition

The study was aimed to determine the iron (Fe) requirements at different growing stages of pot marigold (Calendula officinalis L.). Plants were grown in pots containing equal proportions of sand and perlite, and fertigated with nutrient solution including 4 or 35 µM of the Fe-chelate Fe(III)-EDDHA in each of three different growth stages. Stages were labeled I (from seed germination until 4th to 6th true leaf stage), II (from 4th to 6th true leaf stage until start of flowering) and III (from the start of flowering to flower fading time). Using consistently 4 µM Fe led to chlorotic plants and small and short-lived flowers, whereas using consistently 35 µM Fe led to good quality flowers, considering size, number and lifetime. Results suggest that using 4 µM Fe at growth stages I or III did not result in significant reductions in flower weight and number. Conversely, using 4 µM Fe at stage II led to decreases in flower weight and number. Using 4 µM Fe in two stages could be acceptable only when stages were I and III, although some decreases in number of flowers and number longevity occurred. Results show that it is feasible to reduce the concentration of Fe in the nutrient solution during a considerable part of the plant growth period. Using low Fe in only one growth stage would reduce total Fe inputs by 20–29%, whereas using low Fe in stages I and III would reduce total Fe inputs by 48%. The reduction proposed in the Fe-chelate concentrations would result in diminishing costs for growers and decreasing the environmental impact of Fe fertilization.