Evaluation of synthetic iron(III)-chelates (EDDHA/Fe3+, EDDHMA/Fe3+ and the novel EDDHSA/Fe3+) to correct iron chlorosis

Soil application of synthetic Fe(III)-chelates, mainly those derived from ethylendiamine di(o-hydroxyphenylacetic) acid (EDDHA) and ethylendiamine di(2-hydroxy-4-methylphenylacetic) acid (EDDHMA), is the most effective, but the most expensive practice used to correct iron deficiency in plants growing on calcareous soils. Previous studies that compared the effectiveness of EDDHA/Fe3+ and EDDHMA/Fe3+ always used commercial products and their results are contradictory. In this study, the effectiveness of commercial EDDHA/Fe3+ and EDDHMA/Fe3+ fertilizers to correct iron chlorosis in three different crops (sunflower, peach and pear) was compared using doses calculated with the actual content of chelated iron determined by HPLC. The effectiveness of the Fe(III)-chelate derived from the ethylenediamine di(2-hydroxy-5sulfophenylacetic) acid (EDDHSA), that recently has been marketed as iron fertilizer, was also tested in the sunflower and pear experiments. For the three experiments, several parameters related to the plant iron nutritional status, such as leaf growth, yield, SPAD index (chlorophyll concentration), iron content, Fe/Mn ratio and 50(10P + K)/Fe index were determined. Leaf weight, iron concentration per leaf area, leaf iron content, and K/Ca and 50(10P + K)/Fe ratios were well correlated with the degree of chlorosis, suggesting that these parameters could be used for the diagnosis of the plant iron nutritional status when only iron limited the plant growth. One application of the synthetic Fe(III)-chelates (EDDHA/Fe3+, EDDHMA/Fe3+ and EDDHSA/Fe3+) was enough to cause a visible full recovery from iron-deficiency of the three crops. The EDDHSA/Fe3+ was as effective as the EDDHA/(Fe3+) and EDDHMA/Fe3+ to correct iron chlorosis in the three different crops, growing either in a soil-less system or in field conditions. However, the doses of EDDHA/Fe3+ and EDDHMA/Fe3+ were respectively 1.4- and 1.7-times higher than the EDDHSA/Fe3+. Although these results pointed out the EDDHSA/Fe3+ as a promising iron fertilizer, further research is needed to know technical details related to the application such as doses, timing and frequencies as well as its mobility, distribution and persistence in the environment. Soil-less experiments could be a good and quick tool to test the effectiveness of these iron fertilizers, since there were no differences in the order of effectiveness found for the Fe(III)-chelates between soil (field experiments) and soil-less experiments. (C) 2004 Elsevier B.V. All rights reserved.