Reading a Chelated Micronutrient Label and COA

Buyers meet chelated micronutrients as a bag or a drum with a specification sheet, and the numbers on that sheet decide value more than the marketing does. Two products that both say "chelated iron" can deliver very different amounts of usable metal, depending on the ligand, the chelate percentage and what sits in the insoluble fraction. This guide walks through how to read a label and a certificate of analysis so a purchasing decision rests on chemistry rather than claims.

What the metal percentage actually means

The active metal content — 6% iron, 14% zinc and so on — tells you how much of the product is the nutrient itself. It does not tell you how much of that metal stays available in your soil or tank. A higher metal percentage is not automatically better, because the ligand carrying it and the conditions it meets decide whether the metal remains in a form the plant can use. Read the metal percentage as the starting point, then look at what holds it in solution.

Chelate percentage versus active metal

Chelate percentage describes how much of the metal is present as a protected complex rather than as a free or partly bound salt. A product can show a respectable metal figure yet carry a low chelate figure, meaning much of the nutrient is unprotected and prone to drop out. For soil or liquid feeding where stability is tested, the chelate percentage is often the more useful number. Ask for it expressed clearly, and confirm the method used to measure it, because definitions vary between suppliers.

Ligand types on the market

The ligand is the molecule that holds the metal, and it sets the pH window and the biodegradation profile. EDTA, DTPA and EDDHA dominate conventional supply; amino-acid-based ligands derived from glutamic or aspartic acid sit in the biodegradable group. Each binds a given metal with a different strength and breaks down at a different rate in soil and water. Knowing which ligand you are buying explains most of the price difference and most of the performance difference between apparently similar products.

EDDHA, DTPA, EDTA and amino-acid compared

EDDHA holds iron through alkaline, calcareous conditions where the others weaken, which is why it leads iron programmes on lime soil. DTPA covers a middle pH range and suits many horticultural tanks. EDTA serves acid to near-neutral ground and is widely available. Amino-acid-based chelates offer a biodegradable path and useful stability for programmes where residue limits matter, provided the pH window fits. None is universally right; the soil and water profile choose.

Water-soluble and insoluble fractions

A specification that shows only total metal hides the part that will not go into solution. The water-soluble fraction tells you what actually enters a liquid feed or a soil moisture film; the insoluble remainder may sit in the bag or settle in a tank. For foliar and fertigation use, a high water-soluble figure matters more than a high total. Request the soluble figure explicitly, and treat a product that reports only total metal with caution.

Ortho/para ratio for iron EDDHA

For EDDHA iron, the ortho-ortho isomer carries most of the agronomic value because it forms the most stable complex with iron at high pH. Suppliers who report the ortho/para ratio, or the ortho-ortho content, give you a way to compare products beyond the headline iron percentage. A high total with a low active isomer content may underperform a lower total with a higher active isomer content, so this ratio belongs in any serious buying decision.

Impurities and heavy-metal limits

Trace-element products are made from mineral feeds, and the impurity profile matters where food or export crops are grown. A certificate of analysis should report heavy metals and any arsenic or cadmium figures against the limit that applies to your market. Biodegradable ligands can also carry lower inert load, which helps where receiving-water or soil-load rules are tightening. Keep the impurity statement on file; it is what protects you if a buyer or regulator asks later.

Dry versus liquid formats

Dry granules and powders blend into bulk fertiliser and suit broadcast or banding, while liquids suit fertigation, foliar and in-furrow use. The format changes handling, shelf life and the soluble fraction you can expect. A dry product may need dissolving and filtering before tank use; a liquid may need protection from cold or separation. Choose the format that fits the equipment you already run, because the right chemistry still fails if it cannot pass through your system.

Questions to put to a supplier

Before ordering, ask for the active metal content, the chelate percentage, the ligand type, the water-soluble fraction, the isomer ratio where relevant, and a certificate of analysis with impurity limits. Ask also about registration for your crop and market, shelf life, and pack size. Suppliers who answer with numbers and methods, rather than adjectives, are the ones whose product you can specify with confidence.

Frequently asked questions

Why do two iron products with the same percentage differ? The ligand, the chelate percentage and the EDDHA isomer ratio change how much iron stays available, so the headline metal figure alone does not predict field performance.

What does water-soluble fraction mean? It is the part of the metal that actually dissolves and can enter a liquid feed or soil moisture; the insoluble part may not reach the plant.

Are amino-acid chelates weaker than EDTA? Not necessarily; they offer a biodegradable profile and useful stability within their pH window, and they suit programmes where residue limits matter.

How do I compare suppliers fairly? Request the same set of figures — metal, chelate percentage, soluble fraction, isomer ratio, impurities — and compare like for like rather than brand claims.

Explore the full chelated micronutrient range or review the technical background on chelation before specifying a programme. For tailored advice on product selection and documentation, contact the team at [email protected] or call +86-537-3739818.