EDTA vs DTPA vs EDDHA: Comparison and Application Reference Tables

How to read this table: the pH ceiling is the decisive number

Rank iron chelates by their headline iron percentage and you get the wrong answer in the field. The number that predicts performance is the soil-pH at which the chelate still keeps iron soluble. University of Florida IFAS Extension puts it on a simple 0-to-1 stability scale: at pH 7.5, Fe-EDDHA still holds at 1.0, Fe-DTPA drops to about 0.5, and Fe-EDTA collapses to roughly 0.025. Above pH 6.5, EDTA can no longer be relied on for iron; DTPA stretches the workable range to about pH 7.5; only EDDHA holds iron on calcareous ground past pH 7.5. Match the chelate to your measured soil pH, then compare cost — not the other way around. This page is a quick-reference tool; for the underlying chemistry and the stability curve, see the full mechanism guide linked below.

What RunziChem supplies — and what it does not

To keep this comparison honest: RunziChem supplies the full EDTA chelate line and EDDHA-Fe, but does not supply DTPA chelates. DTPA is included here because buyers ask about it, and a fair comparison needs all three.

• EDTA chelates (in range): EDTA-Zn 15%, EDTA-Fe 13%, EDTA-Cu 14.5%, EDTA-Mn 13%, EDTA-Ca 10%, EDTA-Mg 6%, plus two standard compound EDTA grades — each shipped with a per-batch COA and TDS/SDS, FOB Qingdao.
• EDDHA-Fe (in range): EDDHA-Fe 6% total iron with an ortho-ortho (o-o) content of 4.8% — the o-o fraction is what actually holds iron at high pH, so it is stated explicitly on the spec and confirmed per batch.
• DTPA (not in range): shown for comparison only. If your neutral-to-mildly-alkaline situation points to DTPA, EDDHA-Fe is the RunziChem chelate that also covers that band with margin to spare.

Full specifications sit on the EDTA micronutrients hub and the EDDHA-Fe page.

Match the form to the field: soil-pH × application-method matrix

Application method shifts the answer as much as soil pH does, because foliar sprays largely bypass soil chemistry. The matrix below reads soil pH across the top and application route down the side; each cell is the iron form that stays available under those conditions.

Rule of thumb: don't soil-apply Fe-EDTA on chalky ground expecting it to green up chlorosis — that is EDDHA-Fe's job. For the other micronutrients (Zn, Mn, Cu), EDTA chelates cover the neutral band well, and sulphates are usually the economical foliar choice at any pH.

Application rates: what this page will not invent for you

This is deliberately a comparison-and-selection tool, not a dosing chart. Correct application rates depend on your crop, soil and tissue test, water quality and — critically — the product label and local registration, and they vary widely between crops. Set rates with your local agronomist and a soil/tissue test; typical label ranges vary by crop. For element-specific deficiency thresholds and worked context, use the deficiency and source guides rather than a blanket number:

• Iron Fertilizer Sources: Ferrous Sulphate vs EDTA-Fe vs EDDHA-Fe
• EDTA vs Sulphate vs EDDHA: Choosing the Right Micronutrient Form (mechanism, stability curve, real soil-test thresholds)

Concentration arithmetic (unit conversion only, not a dose): a grade labelled "EDTA-Fe 13%" contains 130 g of iron per kg of product. To reach a 0.1% iron solution (1 g Fe per litre) you would dissolve about 7.7 g of product per litre (1 ÷ 0.13). That is pure unit math to help you read a label — the concentration and volume that are correct for your field must still come from your agronomist and the product label.

Frequently asked questions

EDTA vs EDDHA — which is better for high-pH, alkaline soil?

For iron on soil above about pH 7, EDDHA-Fe is the reliable choice and EDTA-Fe is not. Per UF/IFAS, Fe-EDTA loses iron availability above pH 6.5 (a stability of ~0.025 at pH 7.5), while Fe-EDDHA stays fully available to about pH 9. On acidic to near-neutral ground, EDTA-Fe is the more economical option and EDDHA-Fe would be overspending.

Does RunziChem sell DTPA iron chelate?

No. RunziChem supplies the EDTA chelate line (Zn, Fe, Cu, Mn, Ca, Mg plus two compound grades) and EDDHA-Fe 6% (o-o 4.8%), but not DTPA. DTPA appears on this page only so buyers can compare all three fairly. Where a neutral-to-mildly-alkaline case points toward DTPA, EDDHA-Fe covers the same band with a wider stability margin.

What application rate should I use for a chelate?

There is no single correct rate to quote — it depends on crop, soil and tissue test, water quality, and the product label, and it differs by crop. Confirm rates with your local agronomist and a soil test; treat any figure you see online as indicative until it is checked against your label and local recommendations. Our deficiency guides give context, not prescriptions.