To explain how fulvic acids improve micronutrient uptake, please refer to the example below.
Current research shows that Fe (EDDHA) and similar chelates, despite their high stability, are not perfect. While they can provide ample iron delivery and can assist Fe deficiencies in most cases for these plants, these strong chelates are often very expensive and their use as sole Fe sources might be impractical in traditional agriculture. The use of humic/fulvic acids complemented with either unchelated Fe or with some lower proportion of stronger iron chelates, is a better overall choice in terms of both plant uptake and economic expense.
The effect of fulvic acids and synthetic chelates is synergistic, with both providing advantages that can be complementary. These fulvic acid solutions might also be more favorable for plant species, where the use of highly stable Fe (EDDHA) chelating agents does not treat Fe deficiency symptoms. Fulvic substances are reductive in nature, which means that they will protect Fe2+ from oxidation by either microbes or oxygen dissolved in solution. They are also sometimes able to reduce Fe3+ present in the solution back to Fe2+, which can help with the uptake of this Fe by the plant’s root system.