Iron deficiency (chlorosis) is one of the most common micronutrient problems in agriculture, especially in alkaline and calcareous soils. Two chelated iron products — EDDHA Fe and EDTA Fe — are widely used to correct this deficiency, but they perform very differently depending on soil pH. Understanding the difference helps you choose the right product and save money.
What Is Chelated Iron?
Chelated iron is iron bound to an organic molecule (a chelating agent) that keeps the iron soluble and available for plant uptake. Without chelation, iron rapidly precipitates into insoluble forms in the soil, especially at high pH levels, making it unavailable to plants. The choice of chelating agent determines the effective pH range and cost of the product.
EDTA Fe: Best for Neutral to Slightly Acidic Soils
EDTA Fe (Ethylenediaminetetraacetic acid iron chelate) is the most widely used and cost-effective chelated iron product. Key characteristics:
- Effective pH range: 4.0 – 6.5 (optimal below pH 7)
- Iron content: 13% chelated iron
- Application: Foliar spray, fertigation, and soil application in neutral to acidic soils
- Cost: More economical than EDDHA Fe
- Solubility: Highly water-soluble, compatible with most fertilizers
In soils above pH 7, EDTA loses its ability to keep iron chelated — the iron is released and becomes unavailable. This is the critical limitation of EDTA Fe.
EDDHA Fe: The Solution for Alkaline and Calcareous Soils
EDDHA Fe (Ethylenediamine-N,N’-bis(2-hydroxyphenylacetic acid) iron complex) is specifically engineered for alkaline soil conditions. Key characteristics:
- Effective pH range: 4.0 – 11.0 (remains stable even in highly alkaline soils)
- Iron content: 6% chelated iron (with ortho-ortho isomer being the most effective)
- Application: Primarily soil drench; also suitable for drip irrigation
- Ortho-ortho isomer: Higher o,o content = greater effectiveness; look for 3.0%, 3.6%, or 4.2% o,o values
- Cost: Higher than EDTA Fe, but necessary for alkaline conditions
EDDHA Fe remains fully effective at soil pH up to 11, making it the only reliable chelated iron source for Mediterranean climates, limestone-rich soils, and high-pH irrigation water.
EDDHA Fe vs EDTA Fe: Side-by-Side Comparison
| Property | EDTA Fe | EDDHA Fe |
|---|---|---|
| Effective soil pH | 4.0 – 6.5 | 4.0 – 11.0 |
| Iron content | 13% | 6% |
| Best application | Foliar / fertigation | Soil / drip irrigation |
| Cost | Lower | Higher |
| Alkaline soil suitability | Poor | Excellent |
Application Rates and Timing
Recommended application rates vary by crop and severity of deficiency. General guidelines:
- EDTA Fe (soil application): 2–5 kg/ha, applied before or at planting. For fertigation, 0.5–1.0 g/L in irrigation water.
- EDTA Fe (foliar): 0.5–1.5 g/L solution, sprayed at early signs of chlorosis. Repeat every 10–14 days until symptoms resolve.
- EDDHA Fe (soil application): 1–3 kg/ha for preventive use; 3–6 kg/ha for correction of established deficiency. Apply to the root zone in autumn or early spring.
- EDDHA Fe (drip irrigation): 0.3–0.8 g/L, applied in weekly splits over the growing season.
Early spring soil application of EDDHA Fe — before bud break in fruit trees — is particularly effective because iron must be available at the root zone before rapid canopy growth begins. Waiting until chlorosis appears means the deficiency has already impacted yield potential.
Which Should You Choose?
The decision is straightforward:
- Soil pH below 6.5: Use EDTA Fe — it’s effective and economical.
- Soil pH 6.5 – 11: Use EDDHA Fe — it’s the only chelated iron that stays available.
- Foliar application in any soil: EDTA Fe works well since it bypasses the soil pH issue.
Frequently Asked Questions
Can I mix EDDHA Fe with other fertilizers?
EDDHA Fe should not be mixed with phosphate fertilizers or calcium-based fertilizers in the same tank, as precipitation can occur. Always dissolve EDDHA Fe separately in water first, then add to the irrigation system. EDTA Fe is generally more compatible with fertilizer mixes but should still be tested for compatibility before large-scale application.
Why does EDDHA Fe have a lower iron content (6%) than EDTA Fe (13%)?
The EDDHA molecule is larger and heavier than EDTA, so the iron represents a smaller percentage of the total product weight. However, this does not mean EDDHA Fe is less effective — it delivers iron more reliably in alkaline conditions because the chelate bond remains stable at high pH. On a cost-per-unit-of-available-iron basis, EDDHA Fe is more expensive, but it is the only product that works in alkaline soils.
What is the ortho-ortho isomer and why does it matter?
EDDHA exists in multiple isomeric forms. The ortho-ortho (o,o) isomer is the most effective at chelating iron and maintaining iron availability in the soil. Higher o,o content (expressed as % o,o in product specifications) indicates a more effective product. When comparing EDDHA Fe products, always check the o,o content — products with 4.2% or 4.8% o,o deliver significantly better results than lower-grade products.
Where can I source EDDHA Fe and EDTA Fe in bulk?
Unifarm Chemical supplies both EDDHA Fe and EDTA Fe from China in bulk quantities. EDDHA Fe is available in multiple ortho-ortho values (2.0%, 3.0%, 3.6%, 4.2%, 4.8%). Export documentation and free samples are available upon request.
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Hainan Unifarm Chemical supplies both EDDHA Fe and EDTA Fe in bulk quantities with consistent quality. We offer multiple ortho-ortho values for EDDHA Fe (2.0%, 3.0%, 3.6%, 4.2%, 4.8%) to suit different crop requirements. For a broader overview of chelated micronutrients, see our complete guide to EDTA chelated micronutrients.