The choice of liquid fertilisers you find at your local supplier is endless.

How do you make a choice? Does it matter what form you apply; chelates, suspension concentrates, sulphates or other formulations? Which formulation will give you the most benefits? What type of formulation is the best to use in complicated tank mixes?

The following attempts to explain the differences between formulations on the market and the capabilities of each formulation to help make a better-informed decision. It is heard all too often as to why particular product should or shouldn’t be used and there are so many misinformed explanations of how products are taken into the plant.

Sulphates and other highly water-soluble foliar fertilizers are taken up very quickly by plants, making them an effective and efficient tool for correction of visual/clinical nutrient deficiency.
Once applied there is little if any residual nutrient left behind on the leaf within hours of application.
Sulphates or similar highly water-soluble nutrients can also be highly reactive in the presence of some other nutrients and agricultural chemicals therefore have limited tank mix compatibility with ag chemicals.

A Chelate is a chemical structure which ‘wraps around’ a trace element protecting it from reacting with other nutrients or chemicals. There are many different types of chelate (or complexing) agents and they are not all equal. Below are three common chelating (complexes) sold into the liquids market.

• Fulvic Acid Complex (chelate) – Typically sulphate trace element solution blended with fulvic or humic acid solution. The blend of the trace element and fulvic acid may form a weak single ligand chelate structure which is inferior to EDTA chelates. It may be slightly more stable than straight sulphate formulation. To just add fulvic acid to a sulphate trace element solution does not guarantee all the nutrient is complex (chelated). Fulvic acid may provide some surfactant/adjuvant activity to the formulation to aid nutrient uptake. These solutions are only slightly more stable (better) than a sulphate trace element solution and also have limited longevity in the plant, generally requiring multiple applications throughout the season.

• Lignosulphonate Complex (chelate) – Lignosulphonic acid ammonium salt is a complexing (chelating) agent similar to fulvic acid. This simple one or two ligand structure has a much lower stability than EDTA chelates. These solutions are only slightly more stable (better) than a sulphate trace element solution when tank mixing with ag chemicals and also have limited longevity in the plant, generally requiring multiple applications throughout the season.

• EDTA Chelates are very stable and suitable for tank mixing with ag chemicals. Synthetic chelate molecules such as EDTA, EDDHA, DTPA and others are very large structures; this is the reason for the low analysis of chelated products. Where claims are made for liquid chelates with a microelement analysis greater than 7.5%, be aware these products are not usually fully chelated and may therefore react in tank mixes. EDTA chelates are stable in the presence of phosphate, carbonate and hydroxide anions. Cost per gram of nutrient and cost per hectare is typically much higher than other trace element products.

• Suspension Concentrates (Oxides/Carbonates) allow for a product to have high nutrient analysis e.g. IcON Zinc – 1500g/L. which is significantly higher than chelated or complexed micronutrients and higher than sulphates or nitrates. Uptake characteristics of suspension concentrates are slow release with sustained availability of nutrients for a prolonged period. Suspension concentrates do not contain salts (i.e. no salt index) therefore are less likely to react compared to sulphates. They are highly compatible in tank mixes, cost effective and provide sustained nutrient availability to the plant.

Table 1 below provides a quick and simple guide to the benefits of each formulation. Scale of one to five dots; one being least favorable and five being most favorable attribute.
Table 1: Comparison of different formulations

Uptake into the plant is another frequent discussion around trace element formulations. Things to think of when told that a product doesn’t get taken up rapidly are as follows
• Why do I need all the nutrient delivered in 24 hours?
• Why did I let the deficiency get so bad the plant needs to take up most of the nutrient rapidly?
• Is the amount of element taken up in a short time used by the plant?
• Is there a toxic effect of uptake happening too quickly?
• Is it good for the plant to have a quick dose that doesn’t last long?
• Can I afford to re-apply to keep levels up?

Always ask questions around the formulation of the product you chose to use. Ask for active ingredients and the type of formulation you are applying. Also work out $/ha v’s g/ha and refer back to table 1 to work out if you will require multiple application