Comparison of iron chelates and complexes supplied as foliar sprays and in nutrient solution to correct iron chlorosis of soybean

The application of synthetic chelates is the most efficient remedy for correcting iron (Fe) chlorosis. However, chelates are usually expensive and nondegradable products. Recently, new degradable chelates have been proposed for their use as Fe fertilizers. Also, Fe complexes cheaper than synthetic chelates and derived from natural products are also used to correct Fe deficiencies. Fifteen products, including five different synthetic chelates (Fe-EDDS, Fe-IDHA, and three Fe-EDTA formulations) and ten natural complexes (humates, lignosulfonates, amino acids, glycoproteins, polyamines, citrate, and gluconate), have been compared when applied at low concentration to soybean (Glycine max L.) chlorotic plants grown in hydroponics under controlled conditions. In the first experiment, Fe compounds were applied to the nutrient solution, while in the second trial, Fe was foliar-supplied. Dry matter, Fe concentration in shoots and roots, and SPAD values were used to evaluate the effectiveness of the Fe in the different products. In the nutrient-solution experiment, synthetic chelates provided better plant growth, Fe concentration, and SPAD values than complexes. Among the Fe complexes, transferrin generally provided good plant responses, similar to those obtained with synthetic chelates. After foliar application, the highest regreening was observed for plants treated with synthetic chelates and amino acid complexes, but the translocation to roots only occurred for Fe lignosulfonate. Fe-EDDS and Fe-EDTA performed in a similar way when applied in nutrient solution or as foliar sprays.