As already mentioned in the previous article on what is Iron Sulfate and how to use it , iron is an essential micronutrient for plant growth.As a consequence it should be a good practice to take into account within the usual management of your garden and / or orchard, especially if you observe symptoms of iron chlorosis .
But not all chemical formulas of iron are assimilable: plants can only absorb ferrous ion (Fe2 +), which is very unstable in high pH soils (basic and alkaline soils pH≤ 8) since it quickly oxidizes into ion ferric (Fe3 +) unusable for plants.That is, the addition of iron is not effective if products that ensure the permanence in soluble form of this element in the soil are not used.
The Effectiveness of Iron Chelate
A chelate is nothing other than a substance that forms complexes by joining with metal ions, in this case with the ferrous ion (Fe2 +) that is what interests us.
There are different types of chelates:
- EDTA, DPTA (penthetic acid) and HEEDTA: This group of chelates have poor stability in alkaline soils. Respectively, its protection range is: EDTA: pH 6.5-7; DPTA: pH 4.5-7 and HEEDDTA: pH 4.5-7.
- EDDHA: It is one of the most stable chelates that exist. Depending on its isometry it can be of high stability and long-term efficacy (ortho-ortho) with a pH range of 3 to 11 or of lower stability and rapid response (ortho-para) with a pH range of 3 to 10 Today, ortho-ortho EDDHA is one of the most used in alkaline soils.
- EDDHMA, EDDHSA and EDDCHA: This group, also has high stability, are designed for extreme and highly alkaline soils. PH range ≤ 11. The last two are very soluble and can be used in fertigation.
- IDHA: It is a biodegradable chelating agent.
Taking into account the previous points, how do you choose a good iron chelate?
When choosing a good iron chelate, we must basically look at two important aspects: the richness and the type of chelating agent that form it. This information can be easily found on the product label, in the composition section (see image, SINERGIPRÓN Fe-6 label):
Wealth indicates the proportion, expressed as a percentage of soluble or assimilable iron that the product contains with respect to total iron. That is, the amount of iron that can be absorbed by plants in your garden or orchard.
In general, most chelates have a total iron content of 6%, with wealth being the value that varies according to each product. Depending on the richness and sensitivity to chlorosis of the plants or the crop, we will determine the dose to be applied (see label).
Instead, the type of chelating agent marks the stability and working pH range. As a consequence, it is very important to take into account the pH and the characteristics of the soil or substrate in which the plants are, since, in turn, it will mark the type of agent we will use.
For example: Suppose we have an orchard with an alkaline soil with a pH of 8 (typical of our area), in that case, we would choose an ortho-orthodox EDDHA chelate that would guarantee the permanence of iron in a soluble form in the long term.
If we chose a chelate with a lower pH range, it would not protect the iron and quickly precipitate being unusable for the plants in your garden or orchard, and if we chose one of a higher range, for example, pH ≤ 11, it would also give us problems since Due to the pH of the soil, it would cost you to give up the iron and therefore the contribution of this mineral would be slower and less effective.