Recipe for ferric salts of ethylenediaminetetraacetic Acid.

The supply of iron to plant roots was one of the main problems in water culture until about 1950. The main source of iron was originally ferrous sulfate, already used by Sachs (9). It had to be supplied almost daily to the nutrient solution as it precipitates gradually. Some improvement was obtained with organic compounds, mainly ferric citrate, introduced by Gile and Carrero (4). The favorable effect of natural humates on plants in water culture was noticed by Bottomley (1). Olsen (8) interpreted this as a natural formation of iron humate complexes, resulting in experiments with iron humate. Horner et al. (6) developed a synthetic humate, capable of holding iron in solution. Unfortunately, this humate is difficult to prepare, besides which all humates are of indeterminate composition. Iron humates and other sources such as iron lignin sulfonate (2) and iron metaphosphate (3) gave satisfactory results for certain plants, but none of these compounds has been generally accepted. Alter a publication by Jacobson (7), ferric salts of ethylenediaminetetraacetic acid soon met with general acceptance in water culture. One addition of FeEDTA proved to be sufficient for many weeks. Thanks to Jacobson, FeEDTA became the main source of iron for the greater part of water culture. Jacobson's original recipe is as follows: