What Is a COA in Fertilizer Trade?

The Certificate of Analysis — commonly abbreviated COA — is the document that confirms the chemical composition and physical properties of a fertilizer cargo. It is issued by the supplying entity's quality control laboratory and accompanies virtually every international fertilizer shipment. For buyers, it is the primary quality assurance document against which the contracted specification is measured.

Understanding how to read a COA, what parameters should appear for each product type, and how to identify potential issues is an essential skill for any commercial fertilizer importer. This guide walks through the document structure, parameter by parameter.

A standard COA is a single-page or two-page document on the issuing company's letterhead. It identifies the product (grade, form), the batch or lot number, the production date, the quantity the analysis represents, and the name of the analyst or quality manager who certifies the results. The body of the document is a table of parameters with tested values alongside any specification limits.

The COA should be signed and, ideally, stamped by an authorised signatory of the issuing entity. For international trade, many buyers also request that the COA be notarised or endorsed by the chamber of commerce, though this is not universally required.

For urea 46%, the parameters you should expect to see on a COA include: total nitrogen (reported as % N, should meet or exceed 46.0% on a dry-weight basis), biuret content (reported as %, typically ≤ 1.0% for agricultural grade, ≤ 0.3% for foliar grade), moisture content (typically ≤ 0.5%), and particle size distribution (reported as percentage within a specified mesh range, e.g. 90%+ between 1.0–3.35 mm for prilled or 2.0–4.75 mm for granular).

Some COAs will also report free ammonia, insoluble matter, and iron content. These are secondary parameters but can indicate manufacturing process issues if outside normal ranges. The most critical parameters for trade are nitrogen and biuret.

For compound NPK fertilizers, the COA will report each macronutrient individually: total nitrogen (N%), total phosphorus as P2O5%, and total potassium as K2O%. It should also report water-soluble phosphorus as a fraction of total P2O5, moisture content, and sometimes individual nutrient forms (ammoniacal N vs. nitrate N).

For grades with secondary nutrients — sulphur (S), magnesium (MgO), calcium (CaO) — these will appear as additional rows. The guaranteed analysis figures on the bag label are typically lower than the tested COA values; the COA reflects the actual batch result while the label shows the minimum the seller commits to.

For DAP (18-46-0), the COA should confirm nitrogen ≥ 18% and total P2O5 ≥ 46%, with a high water-soluble P fraction (typically 80%+ of total P2O5). Moisture should be low (typically ≤ 2.5%). Free acid content is sometimes reported and should be within acceptable limits.

For MAP (12-61-0), nitrogen is lower (approximately 12%) and phosphorus is higher (approximately 61% P2O5). The very high P2O5 content of MAP means even small deviations from specification represent significant nutrient shortfall per tonne. MAP is often used as a blend component, so specification accuracy is critical for downstream blend quality.

This is a critical distinction that many buyers overlook. The COA is produced by the seller's own laboratory and represents the seller's analysis of the product. It is not independently verified. The pre-shipment inspection certificate, issued by SGS, Intertek, Bureau Veritas, or an equivalent independent body, is based on samples collected from the actual cargo at the load port by a third party who has no commercial interest in the result.

An independent inspection certificate is a significantly stronger quality assurance tool than a COA alone, because it eliminates the possibility that the COA does not represent the actual loaded cargo. For large transactions, new supplier relationships, or markets where product quality is a known risk, requiring both a COA and an independent inspection certificate is best practice.

Several warning signs suggest a COA may not be trustworthy. Perfectly round numbers (exactly 46.00% N, exactly 1.00% biuret) with no decimal variation are unusual in real laboratory analysis. COAs with no lot number or batch reference, no analyst signature, or no date of analysis are procedurally deficient. COAs from unverifiable laboratory names or with inconsistent formatting should be treated with caution.

If a supplier provides a COA that does not correspond to the specific cargo you are buying — for example, a COA dated many months earlier or referencing a different quantity — request a current COA for your specific shipment batch. Each production run should have its own COA.