Iron in the fertigation of fruit trees
Iron (Fe) in the fertigation of fruit trees
Why chelated iron is needed
In calcareous soils with a high pH — the norm across northern Greece — iron is converted into insoluble forms (Fe(OH)₃) and is not available to the root, producing iron chlorosis: yellowing between the veins of the young leaves. Supplying chelated Fe through the drip system keeps the iron soluble so that the roots can take it up.
Chelate stability against soil pH
Every chelating agent holds iron in solution only up to a certain pH — above it the Fe precipitates and the product stops working.
stable to ~6.5
stable to ~7.0–7.5
stable to pH 9
The four main chelated iron forms
Fe-EDDHA
- The most suitable form for calcareous and alkaline soils
- Critical: ask for a high percentage of the ortho-ortho isomer — that is the active fraction
- Ideal for drip irrigation — it does not precipitate in the emitters
- Long-lasting effect, fewer repeat applications
Fe-HBED
- Stability comparable to EDDHA on alkaline soils
- Less widely available commercially in Greece — check supply first
- A good alternative to EDDHA where it can be obtained
Fe-DTPA
- Intermediate stability — suitable for slightly alkaline soils
- Above pH 7.5 it begins to break down
- A good choice where the irrigation water has a moderately high pH
Fe-EDTA
- Suitable only for acid or neutral soils
- On alkaline soils it precipitates very quickly — poor performance
- Can be combined with local acidification of the irrigation water
How it is applied through fertigation
Order of operations: irrigate first with clean water for 10–15 minutes → inject the Fe solution in the middle of the irrigation cycle → carry on with clean water for a further 15–20 minutes, so that the iron is carried down into the root zone and the lines are flushed clear.
Timing through the growing season
Before bloom
First application shortly before bud swell
Fruit set
Second application as fruit and shoot growth begins
Rapid growth
Third application if chlorosis appears on new leaves
Fruit development
Optional top-up on strongly calcareous blocks
Indicative Fe-EDDHA rates (6% Fe, ortho-ortho) for fruit trees
| Tree age / size | Elemental Fe per tree per year | Number of applications | Comment |
|---|---|---|---|
| Young trees (1–3 years) | 1–2 g Fe (≈17–33 g of a 6% Fe-EDDHA product) | 1–2 | Small rhizosphere, lower rate |
| Trees in full development (4–10 years) | 2–4 g FeMost common rate (≈33–67 g of a 6% Fe-EDDHA product) | 2–3 | Splitting into 2–3 applications improves effectiveness |
| Mature / large trees (over 10 years) | 4–6 g Fe (≈67–100 g of a 6% Fe-EDDHA product) | 2–3 | Under severe chlorosis, adjust to the leaf symptoms |
| Expressed per unit area (guideline) | ≈1–5 kg Fe/ha/year (≈20–80 kg of a 6% Fe-EDDHA product per ha) | – | Follows from the per-tree rate multiplied by planting density |
The rates are indicative, based on the literature for chelated Fe-EDDHA on fruit trees; the exact rate is set after leaf and soil analysis and after observing the symptoms. The grams of product are calculated for a formulation containing 6% Fe — if the product to hand has a different content, the quantity is adjusted accordingly.
Scientific background / indicative bibliography
Lucena, J.J. (2003). Fe chelates for remediation of Fe chlorosis in strategy I plants. Journal of Plant Nutrition. | Álvarez-Fernández et al. (2005). Effects of Fe chelates on micronutrient uptake. Journal of Plant Nutrition. | Rombolà & Tagliavini (2006). Iron nutrition of fruit trees. In: Iron Nutrition in Plants and Rhizospheric Microorganisms, Springer. | On the ortho-ortho EDDHA fraction: García-Marco et al. (2006), European Journal of Agronomy. Rate ranges adapted from the technical guidance of Fe-EDDHA manufacturers for fruit trees in European practice.Related articles
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