“Oils ain’t oils”, as many will long recall, and when it comes to supplying iron for plant nutrition according to your soil’s pH level, “chelates ain’t chelates” either.
Sheri Robinson, southern agronomist with specialty fertiliser supplier Haifa Australia, said iron was available in a full range of chelates and unless growers were applying the correct chelate for their soil type, they could be “wasting their time and money”.
She said to take this a step further, when using the EDDHA chelate for iron, “stability ain’t stability” and said growers needed to check stability components to ensure they maximised plant production benefits and their return on investment in this iron chelate.
“Ortho-ortho is the shape of the EDDHA and is the most stable form in soil, so growers need to check the ortho-ortho percentage of this chelate, rather than just the total iron percentage.”
In ortho-ortho iron, the chelating agents ‘binds’ iron in a more stable way as it does not allow water to polarise and destabilise the particle.
“Ortho-ortho is the best for keeping the chelate in the soil solution, including in higher pH calcareous soils, so the level of this is more important than the total,” Ms Robinson said.
“An EDDHA iron chelate may have a total iron percentage of six, but it may only have a 4.8 per cent ortho-ortho component, leaving 1.2 per cent as ortho-para or para-para, which are components that are not as strong.
“Ortho-ortho of 4.8 per cent has generally been the highest level available in iron chelates, with many offering levels of 3–4 per cent, however Haifa Australia now offers an EDDHA iron chelate with an ortho-ortho level of 5.2 per cent.
“EDTA chelates are the most cost-effective and widely used, however EDTA iron also is the least stable in soils and should only be used where soil pH is up to 6–6.5.
“EDDHA iron chelates are suitable for soils up to 9 pH; while other iron chelates include DTPA, suitable for soils up to 7 pH, and HBED, which is suitable for up to level 12 pH soils.
“The two-part message for growers is if you are putting out an iron EDTA to soil pH above 6–6.5, you are wasting your money because it becomes bound and precipitates and, therefore, unavailable to plants, so use an EDDHA iron chelate,” Ms Robinson said.
“And look at the ortho-ortho stability component, because the total iron percentage is not relevant. There is widespread potential for growers to improve crop production and quality through better iron use efficiency according to their soil pH.
“Some almond growers who have since understood the importance of the ortho-ortho have said ‘wow, look at how green my almond trees are’, particularly when adding magnesium with the iron, which is helping the chlorophyll green-up the plants. Improving photosynthesis will improve performance.”
Ms Robinson said sunlight was another important factor to consider when applying iron chelates because it could cause iron loss from the product.
“If possible, growers need to keep their tanks covered for its stability. You also need to be thinking of things like what you are using, keeping lids on containers, mixing it last and not under UV light.”
In addition to iron chelates, Haifa Australia also now offers zinc and manganese EDTA chelates, as well as boron and molybdenum micronutrients, to help growers maximise their cropping performance.
“Micronutrients are available within our stable of fertiliser products, however we now have the ability to bolster their supply. It gives growers flexibility to address the specific needs for their region,” Ms Robinson said.
“Instead of having to source micronutrients elsewhere, we can now supply the additional nutrition and also create specific micronutrient blends according to growers’ regional requirements and cost-effectiveness.
“They could apply an NPK product and use a micronutrient blend that could include zinc and manganese EDTA chelates, and they could choose an iron chelate that suits their soil pH level.
“While various EDTA chelating agents used a sodium attachment, Haifa Australia can offer EDTA chelates with more favourable potassium or nitrogen attachments.
“Not surprisingly, Haifa Australia is becoming a strong new option in the country’s micronutrients market.”
