Comparative study of the efficacy of commercial Fe chelates using a new test

Abstract

At present, more than 100 iron fertilizers are on the Spanish market. The most efficient ones contain Fe‐EDDHA or Fe‐EDDHMA chelates as the basic component; however, different formulations cause plants to respond differently. In a previous paper we developed a new test to evaluate the relative stability of the Fe fertilizers against high pH (11.5) and competition with an excess of DTPA. In the present work, 31 formulations of chelates with red color (absorbance near 480 nm) are compared. Besides the application of the test, spectral properties, pH in solution and Fe content of the products have also been studied. Most of the commercial chelates present a similar behaviour after the test application, except that some of them have a greater resistance to competition with the DTPA. A few were largely destroyed after the test application. No significant differences were observed between Fe‐EDDHA and Fe‐EDDHMA fertilizers due to a large variability among chelates with the same base but different formulation. We conclude that most of the chelate fertilizers used in this study behaved similarly because of their analogous formulation. The test was found to be useful in establishing the relative stability of “red chelates”; in this way, comparing them was an easier task.