The United States Department of Agriculture has discovered a ‘greener’ alternative to a fertiliser additive, which is currently believed to contribute to the accumulation of heavy metals in waterways.

Whilst some crops, particularly ornamental nursery and floral crops, require micronutrients like iron, manganese, copper and zinc, fertilizers that provide these micronutrients often include synthetically produced compounds that bind with the micronutrients so they are available in the root zone. The most commonly used compounds, known as chelating agents, are not readily biodegradable, and can extract metals from sediments.

Their use is believed to increase pollution of waterways, by increasing the amount of iron that flows into and becomes soluble in water. The process is not only causing problems in the United States; concerns in Europe about one such binding agent, EDTA, have prompted calls for the immediate switch to alternatives.

Joseph Albano, a horticulturalist at Agricultural Research Service (ARS) U.S. Horticultural Research Laboratory in Florida, has published research which he believes shows the potential of a more environmentally sound alternative to the damaging binders. Albano's alternative chelating agent is known as EDDS. It is a natural compound that is biodegradable and less likely to persist in the environment.

In a series of studies, Albano grew marigolds in standard soil-less potting media using fertilizers formulated with EDDS or one of two commonly used chelating agents: EDTA and DTPA. Each of the three treatments was chelated with iron so Albano could assess the effectiveness of EDDS as a fertiliser iron source.

The results showed that EDDS was a suitable chelating agent for use in fertilisers. There were no differences in plant growth or leaf-tissue iron levels among plants grown with iron-EDDS, those grown with iron-EDTA, or those grown with iron-DTPA fertilisers. The new chelate was also shown to have a much faster rate of photodegradation (degrading when exposed to light) than traditional binders.

Albano said the work can be expected to shift the use of chelates in a more sustainable direction in floral and nursery crop operations.

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