Why the Fertilizer Industry Is Looking Beyond EDTA Chelates
EDTA chelates have been widely used for decades to deliver micronutrients such as iron, zinc, manganese and copper to plants.
Their advantage is clear: EDTA forms relatively stable complexes with metal ions, helping keep micronutrients soluble and available under many fertilizer application conditions.
However, EDTA also has an important limitation.
It is not readily biodegradable under standard OECD criteria, and its persistence in soil and water has become an increasing environmental consideration.
European Chemicals Agency data indicate that EDTA and several EDTA metal salts do not meet the criteria for ready biodegradability. EDTA can ultimately degrade, but degradation in soil can be slow and strongly dependent on environmental conditions. ECHA data report only around 10–12% degradation after four weeks in some soil studies, increasing to 32–45% after 15 weeks and at least 65% after 45 weeks.
This environmental persistence is one reason researchers are actively investigating biodegradable alternatives to conventional EDTA-based micronutrient fertilizers.
One of those alternatives is gluconate.
Why Gluconate Is Attracting Attention
Gluconic acid and gluconates are already well known as metal-complexing compounds.
The European Commission’s Expert Group for Technical Advice on Organic Production has specifically described gluconic acid as a complexing agent capable of binding metals or salts and modifying their solubility and plant availability.
The same European technical assessment discusses gluconic acid and gluconates in the context of fertilizer applications and micronutrient availability.
This is important because micronutrients such as:
| Micronutrient | Traditional EDTA Product | Gluconate Alternative |
|---|---|---|
| Iron | Fe-EDTA | Ferrous / Iron Gluconate |
| Zinc | Zn-EDTA | Zinc Gluconate |
| Manganese | Mn-EDTA | Manganese Gluconate |
| Copper | Cu-EDTA | Copper Gluconate |
can potentially be delivered through a different complexing system.
Gluconate does not behave exactly like EDTA, and it should not be considered a simple 1:1 replacement. However, increasing research suggests that gluconate-based micronutrients can be valuable alternatives under suitable formulation and application conditions.
The Major Difference: Biodegradability
The environmental difference between gluconate and EDTA is significant.
According to data published in an ECHA registration dossier, sodium gluconate achieved approximately:
61% biodegradation after 3 days, 74% after 7 days, and 89% after 28 days.
The study concluded that sodium gluconate is readily biodegradable according to the test conditions.
By comparison, EDTA and several EDTA-metal complexes are generally classified as not readily biodegradable under OECD screening criteria.
This does not mean that EDTA is prohibited or inherently unsafe.
It means that for fertilizer manufacturers seeking lower-persistence complexing agents, gluconate offers a fundamentally different environmental profile.
This distinction is increasingly relevant in:
foliar fertilizers, liquid micronutrient formulations, fertigation products, hydroponic nutrients and sustainable agriculture formulations.
Scientific Research Has Already Compared Gluconate Systems with EDTA
Gluconate-based micronutrients are not just a theoretical idea.
Researchers from the Autonomous University of Madrid have directly investigated gluconate and heptagluconate complexes as alternatives to conventional synthetic chelates.
A study first published online in 2019 (2020 journal issue) evaluated Fe-gluconate and Fe-heptagluconate complexes under hydroponic and calcareous-soil conditions and compared their performance with synthetic Fe chelates including EDTA.
The researchers concluded that the effectiveness of biodegradable Fe complexes depended strongly on ligand type and the metal-to-ligand ratio. Certain heptagluconate formulations were identified as potential environmentally friendly alternatives to less degradable synthetic chelates.
This finding highlights an important point for fertilizer formulators:
Replacing EDTA is not simply a matter of exchanging one kilogram of EDTA chelate for one kilogram of gluconate. Formulation chemistry matters.
Metal concentration, pH, ligand-to-metal ratio, water quality and application method all influence performance.
Manganese Research Shows the Same Direction
A later study from the same research group examined manganese nutrition using Mn-gluconate and Mn-heptagluconate, with Mn-EDTA used as a reference.
The complexes were tested on manganese-deficient soybean under hydroponic and calcareous-soil conditions.
The researchers found that selected biodegradable complexes could effectively provide manganese to plants. In particular, optimized Mn-heptagluconate formulations were identified as biodegradable alternatives to EDTA.
At the same time, the study demonstrated that ordinary gluconate formulations were sensitive to ligand ratio and could affect the uptake of other micronutrients if the formulation was not properly optimized.
This is another reason why gluconate products should be evaluated through controlled formulation trials rather than simple weight-for-weight substitution.
Not Every Soil Condition Favors Gluconate
A credible comparison must also acknowledge the limitations.
A 2015 study published in Frontiers in Plant Science compared traditional chelating agents including EDTA, DTPA and EDDHA with biodegradable and natural complexing agents including gluconate.
Under highly calcareous soil conditions, traditional synthetic chelates generally maintained some micronutrients in solution more effectively than gluconate.
The researchers nevertheless identified gluconate as an interesting alternative because of its high biodegradability and lower environmental persistence.
Therefore, gluconate should not be marketed as universally superior to EDTA.
The more accurate conclusion is:
EDTA offers stronger complex stability in demanding alkaline conditions, while gluconate can offer advantages where biodegradability, short-term nutrient availability and environmental profile are important.
Where Gluconate Can Be Particularly Interesting
Gluconate-based micronutrients may be especially suitable for applications where the fertilizer is prepared and used relatively quickly rather than stored for extended periods in strongly alkaline conditions.
Examples include acidic or mildly acidic irrigation water, fertigation solutions, foliar sprays, hydroponic systems and short-residence-time liquid formulations.
Under these conditions, a highly persistent synthetic chelating agent may not always be necessary.
For example, a fertilizer formulation diluted into water at approximately pH 4–5 and applied within 24–48 hours presents a very different chemical environment from a micronutrient fertilizer expected to remain stable for months in alkaline solution or strongly calcareous soil.
This is exactly why application-specific testing is important.
Zinc Gluconate Is Also Gaining Agricultural Research Interest
Recent research is expanding beyond iron and manganese.
A 2024 study published in Plant Biotechnology investigated foliar applications of zinc gluconate, iron gluconate and copper gluconate.
The researchers evaluated their effects on Tomato Mosaic Virus infection in Nicotiana benthamiana and tomato plants.
Zinc gluconate showed the highest disease-control activity among the tested gluconate micronutrients and did not cause clear phytotoxic effects under the study conditions. The researchers concluded that zinc gluconate showed potential for agricultural applications.
This research does not prove that zinc gluconate should replace Zn-EDTA in every fertilizer.
It does, however, provide additional evidence that zinc gluconate is biologically active in foliar agricultural applications and deserves further evaluation as a micronutrient source.
Copper Gluconate Has Agricultural Applications Too
Copper gluconate has also been investigated in crop protection.
Field and laboratory research evaluating copper gluconate against citrus canker found that selected copper gluconate treatments achieved efficacy comparable with conventional copper treatments under the experimental conditions.
The study suggested that a copper gluconate formulation at approximately 1:1000 dilution could be effective for managing citrus canker.
Although crop protection and micronutrient fertilization are different applications, this research confirms that copper gluconate is already being investigated as a functional agricultural compound.
Gluconate vs EDTA: The Correct Way to Compare Cost
One common mistake is to compare the price per metric ton of EDTA chelate directly with the price per metric ton of gluconate.
This can be misleading.
For example:
An EDTA-Zn fertilizer may contain approximately 15% elemental Zn, while a zinc gluconate product may contain around 12–14% Zn, depending on specification.
Likewise, EDTA-Fe and ferrous gluconate have different elemental iron contents.
The correct comparison is therefore:
cost per kilogram of elemental micronutrient delivered, combined with actual agronomic performance.
A serious formulation study should compare:
elemental Fe/Zn/Mn/Cu concentration, water solubility, solution stability, precipitation, pH compatibility, crop response and total formulation cost.
Only after these factors are considered can a manufacturer determine whether partial or complete replacement of an EDTA chelate is commercially justified.
EDTA Is Not Disappearing — But the Market Is Looking for Alternatives
EDTA remains an effective and widely used chelating agent.
Its strong complex stability means that it will continue to be important in many fertilizer applications, particularly where high pH and difficult soil chemistry require stronger chelation.
But the direction of agricultural research is increasingly clear.
Researchers are actively investigating biodegradable complexing agents because conventional EDTA-based systems can persist much longer in the environment.
Gluconate is one of the most practical candidates because it combines:
metal-complexing ability, high water compatibility, rapid biodegradability and existing use in Fe, Zn, Mn and Cu compounds.
For some formulations, this could make gluconate not simply another micronutrient salt, but part of a broader transition toward more biodegradable micronutrient delivery systems.
A Practical EDTA-to-Gluconate Evaluation Strategy
For fertilizer manufacturers currently using EDTA chelates, the safest strategy is not immediate replacement of the entire formulation.
A more practical approach is to evaluate one micronutrient at a time.
A typical development program could begin with EDTA-Fe versus Ferrous Gluconate, followed by EDTA-Zn versus Zinc Gluconate, EDTA-Mn versus Manganese Gluconate, and finally EDTA-Cu versus Copper Gluconate.
Each comparison should use equivalent elemental metal dosage rather than equal product weight.
Testing should include solution appearance immediately after preparation and after 24–48 hours, precipitation or sedimentation, pH stability, compatibility with irrigation water, foliar compatibility and crop response.
This approach allows fertilizer manufacturers to determine where gluconate provides a genuine technical and economic advantage rather than relying on theoretical comparisons.
Gluconate Micronutrients for Agricultural Formulation Development
WIS Biotech supplies a range of gluconate-based micronutrient ingredients for customers developing agricultural, fertilizer and plant-nutrition formulations, including:
Ferrous Gluconate, Zinc Gluconate, Manganese Gluconate and Copper Gluconate.
For customers currently using EDTA-Fe, EDTA-Zn, EDTA-Mn or EDTA-Cu, the most effective development strategy is to evaluate gluconate products under the customer’s actual water quality, pH, dilution ratio and application conditions.
Rather than claiming that gluconate is a universal replacement for EDTA, we recommend application-specific testing based on equal elemental micronutrient dosage.
Technical documents, COA, specifications and trial quantities can be supplied for formulation evaluation.
References
López-Rayo S., Nadal P., Lucena J.J. Reactivity and effectiveness of traditional and novel ligands for multi-micronutrient fertilization in a calcareous soil. Frontiers in Plant Science, 2015. DOI: 10.3389/fpls.2015.00752.
Islas-Valdez S., López-Rayo S., Lucena J.J. Effect of Fe:ligand ratios on hydroponic conditions and calcareous soil in Solanum lycopersicum L. and Glycine max L. fertilized with heptagluconate and gluconate. Journal of the Science of Food and Agriculture, 2020. DOI: 10.1002/jsfa.10119.
Islas-Valdez S., López-Rayo S., Lucena J.J. Implications of the Mn:ligand ratio for Mn uptake by Glycine max L. plants fertilized with heptagluconate and gluconate complexes. Journal of the Science of Food and Agriculture, 2021. DOI: 10.1002/jsfa.11110.
Narusaka M., Narusaka Y. Zinc gluconate protects against plant virus infection in tomato and Nicotiana benthamiana plants. Plant Biotechnology, 2024. DOI: 10.5511/plantbiotechnology.24.0628a.
European Chemicals Agency. Sodium gluconate biodegradation data: 89% degradation after 28 days; classified as readily biodegradable.
European Commission, Expert Group for Technical Advice on Organic Production. Technical assessment of gluconic acid, calcium gluconate and magnesium gluconate as complexing agents in fertilizer applications.
Zhang Y. et al. Laboratory Bioassay and Field Evaluation of Copper Gluconate as a New Potential Bactericide Against Xanthomonas campestris pv. citri (Hasse) Dye. Journal of Agricultural Science, 2013. DOI: 10.5539/jas.v5n12p23.