 |
| Chelated Trace Elements |
|---|
Trace elements
Plants take up a number of different elements as food. Some are taken up in much larger quantities than others.
Those that are taken up in the largest quantities are called major or primary elements. These are nitrogen (N), phosphorus (P) and potassium (K).
Then there are the secondary elements. These are calcium(Ca), sulphur (S) and magnesium (Mg).
Finally there are the trace elements (also called micronutrients). These are required in small quantites by the plant, but they are still essential for plant health and production. The trace elements are Copper (Cu), Iron (Fe), Manganese (Mn), Molybdenum (Mo) and Zinc (Zn).
Chelated trace elements
Iron (Fe) is a reactive metal. In concentrated solution it will react with other fertiliser elements, particularly phosphorus (P) to form an insoluble compound. Being insoluble this compound cannot stay dissolved, so it falls out of solution as a sediment. To prevent this happening, iron can be chelated. This is a process whereby the iron is incorporated into the structure of an organic acid molecule (a chelating agent). Chemical bonds hold the iron in place within the structure of the chelating agent and prevent it from reacting with other elements. The chelated iron remains available to the plants, so its property as a fertiliser is not impaired.
Chelated iron is therefore a form of iron which can be mixed into a fertiliser solution and it will stay in solution. More than that, when the fertiliser solution is applied to the soil, then a suitable chelate can ensure that the iron stays in the soil solution and is available to the plant for uptake through the roots. Without this the iron can be lost, often being locked into the clay lattice within the soil and rendered unavailable to the plant.
Iron is the most reactive trace element, and the need for chelation is very clear. Other metals, copper (Cu), manganese (Mn) and zinc (Zn) can also be chelated and this ensures that they do not react in any tank mixture, or in the soil, and so remain fully available to the plant. Another important reason to chelate these other metals is that if they are included in a concentrated fertiliser solution as simple sulphates along with chelated iron , there is a tendency for the chelating agent to exchange its hold on the iron with one of these other metals. So the chelate releases the iron , which is then free to react and is lost from the solution. By chelating all these other metals it ensures the stability of the whole fertiliser solution and ensures overall efficient feeding.
Types of chelate
There are many different types and qualities of chelate. There are traditional natural chelates such as citric acid or oxalic acid, and there are complex modern synthetic chelates.
The value of a chelate is determined by:
a) How much metal it can hold in its structure
b) How strongly it holds the metal
c) Resistance to degredation in alkaline conditions
|
|
|
|
 |
The choice of chelate is determined by how the product is to be used (soil, water or foliar application) and - especially - the pH levels of the soil or growing medium.
There are 3 common chelates used in commercial horticulture, and each has a specific purpose:
| Solufeed product | Chelate type | Application |
|---|
|
Solufeed Fe13 (13.2%) | EDTA soluble powder | Foliar applications. Irrigation water pH<6.5 | |
Solufeed Fe7 (7%) | DTPA soluble microgranule | Irrigation water pH<7.5 | |
Solufeed Fe6 (6%) | EDDHA soluble microgranule (high ortho ortho isomer) | Soil applications Irrigation water <pH9.5 | All Solufeed iron chelates are fully compatible with NPK fertilisers.
EDTA e.g. Solufeed Fe 13 EDTA soluble microgranule or Solu-7 liquid
An effective chelate for all reactive metals. Relatively inexpensive. If applied to the leaves there is some useful foliar uptake. Not very effective for soil application, but alright for inert growing media like peat. Fe EDTA is stable up to a pH of about 6.5, so it is particularly suitable for glasshouse hydroponic systems where the pH is controlled. The other metals are very stable (up to pH 9) and this is really the only chelate available or needed for Cu, Mn and Zn.
DTPA e.g. Solufeed Fe 7 DTPA soluble microgranule of DTPA 3.5 liquid
Stable up to pH of 7.5. A bit more expensive than EDTA. Has less foliar activity than EDTA but improved activity in soil. Popular in glasshouse hydroponic production in some countries (e.g. Holland) even where automatic control systems means the solution never gets close to the pH of 7.5 since growers believe the iron is more stable and available.
EDDHA e.g. Solufeed Fe6 EDDHA soluble microgranule
Stable up to a pH of 9.0. This is the most stable of all the commonly available iron chelates, and it is the one to choose for use in soil. It has the power to hold iron in the soil solution and keep it available to the plant. Has no foliar uptake, so is only absorbed through the roots. Suprisingly, EDDHA does have a role in glasshouse hydroponic systems, even when the pH of the growing solution never comes close to pH 9.0. EDDHA is seen as the most stable and available form of iron , and is used to boost iron availability particularly when the temperature is low e.g in early spring when there can be bright sunshine on the leaves, causing a demand for iron , but the hydroponic solution is still quite cold. Since the uptake of iron by the plant is an active process, plants are less able to take up iron if the roots are cold. The ready availability of EDDHA helps to overcome this problem.
There are various forms (isomers) of the EDDHA molecule, and some are better at holding the iron into the structure of the molecule than others. For this reason claims are often made as to the beneficial "ortho-ortho" isomer content of the EDDHA.
There are 2 variant types of EDDHA. These are EDDHSA (sulphate derivative) and EDDHMA (methyl derivative). These variants are similar in characteristics to EDDHA. All are recognised as EU fertilisers according to the regulations.
|
|
