The effectiveness of iron-amino acid complexes (Fe-BAA) synthesized by using amino acids extracted from chemical hydrolysis of blood proteins as Fe source for cucumber (Cucumis sativus L.) was compared with Fe-EDTA, Fe-lysine (Lys), and Fe-methionine (Met) complexes. Three individual nutrient solution experiments were conducted. In Exps.1 and 2, cucumber was grown in Fe-free nutrient solution and different Fe fertilizers were applied as foliar spray before and after appearance of Fe-deficiency symptoms on the leaves, respectively. In Exp. 3, Fe was used in the root nutrient solution (Exp. 3). Regardless of the method and time of Fe application, all Fe fertilizer sources significantly increased the shoot dry mass of plant as compared with no added Fe control. In Exps. 1 and 2, the Fe-BAA was the most effective source of Fe for prevention or correction of Fe deficiency in cucumber and resulted in the highest root and shoot biomass. The plants receiving Fe-BAA exhibited the highest concentration of Fe and chlorophyll as well as the highest activity of Fe-containing enzymes catalase (CAT) and ascorbic peroxidase (APX) in their leaves. In Exp. 3, Fe-EDTA and Fe-BAA were similar in their effectiveness as Fe source. In all experiments, the Fe-Met was less effective than the other Fe fertilizer sources. The Fe-BAA was found to be an effective Fe fertilizer source for cucumber. Further studies are needed to improve the ability of Fe-BAA and other Fe-AA complexes to maintain desired levels of Fe in nutrient solution.
