MAP or DAP: how to choose between them
MAP and DAP are the two phosphate fertilizers most buyers end up choosing between, and the comparison is usually made badly. The grade numbers look similar, the price difference is usually small, and the decision gets made on the day’s quotation.
Five criteria actually decide it. Price is the fifth.
1. Nutrient content
MAP 11-52-0 — 11% nitrogen, 52% available P2O5, no potassium. DAP 18-46-0 — 18% nitrogen, 46% available P2O5, no potassium.
MAP carries six percentage points more phosphate per tonne and seven fewer of nitrogen. Per tonne of product, MAP delivers about 13% more P2O5. That matters on a long freight leg, where you are paying to move nutrient, not filler.
But DAP’s nitrogen has value. If the crop needs nitrogen at planting anyway, DAP’s 18% is nutrient you would otherwise buy separately. If it does not, you have paid for nitrogen and freighted it to a field that did not want it. That calculation, done properly, often reverses the conclusion that the cheaper-per-tonne product suggests.
2. Storage behaviour
This is where the two genuinely differ, and where buyers most often get caught.
MAP is chemically acid and does not absorb moisture the way DAP does. It stays free-flowing in a humid warehouse, and it does not set in the bag.
DAP is more hygroscopic. In a humid climate, over a long storage period, or in a bag that has been handled roughly, DAP takes up moisture and cakes. Once a bag has caked, it has to be broken up before it can be spread, and the cost of that labour is never in the purchase price.
If the material will sit in a warehouse for months before use, or if the destination is tropical, this criterion alone can decide the specification.
3. Blending compatibility
MAP can be blended with urea. DAP cannot.
DAP and urea in the same bag release ammonia. Nitrogen is lost, the blend cakes into a mass, and the analysis on the label no longer matches what is in the bag. This is the most expensive single mistake in fertilizer blending, and it is entirely avoidable.
MAP and urea coexist without that reaction, which is why blend plants in humid climates standardise on MAP as their phosphate source whenever the compound contains nitrogen.
If the phosphate is going into a mechanical blend with urea — which most NPK blends are — the decision is effectively made for you.
4. Soil reaction
MAP is acid-forming at the granule surface; DAP is alkaline. On an acidic soil, DAP’s reaction is an advantage. On a high-pH calcareous soil, the ammonia component of DAP can be lost to volatilisation if the material is not incorporated, and MAP is the safer choice.
Repeated use of either on an already-acidic soil will pull pH down over several seasons, and below about pH 5.5 the phosphate binds with aluminium and iron and becomes unavailable. That is an agronomic problem — lime, organic matter, placement — not a product choice.
5. Cost per unit of phosphate
The comparison that matters is delivered cost per tonne of P2O5, not price per tonne of product.
Take the FOB price, add freight to your port, divide by the P2O5 content, and compare. Then adjust for the nitrogen in DAP: if you would have bought that nitrogen anyway, credit it; if not, do not.
Doing that arithmetic properly usually shows the two products within a few percent of each other on a phosphate basis, which means the decision should be made on criteria 1 to 4 and the price should only break a tie.
The decision, in order
- Will it be blended with urea? If yes, MAP. This settles most cases.
- Will it be stored for months in a humid climate? If yes, MAP.
- Is the soil acidic and is nitrogen also wanted at planting? If yes, DAP.
- Is the freight leg long? MAP’s higher concentration favours it.
- Only now compare delivered cost per unit of P2O5.
What to write into the contract
Whichever you choose, the specification needs more than the grade:
- Analysis, with the basis stated: available P2O5, and the test method
- Water-soluble P2O5 as a percentage of available
- Moisture limit — do not leave it to “normal”
- Granule size band and tolerance (if it will be blended)
- Crushing strength
- Packaging, liner, marks and loaded quantity per container
- Documents the shipment will carry, confirmed item by item
A quotation that names a grade and a price is a starting point. A quotation that carries those seven points is something you can compare against another supplier’s.
The agronomic and handling differences described here are properties of the products. Prices are not quoted — ask the export desk for a comparison against your own cargo.
Questions buyers ask
Is MAP better than DAP?
Neither is better in the abstract. MAP carries more P2O5 per tonne and is stable in storage and in blends; DAP carries more nitrogen and is alkaline, which suits acidic soils. The choice depends on the soil, the storage conditions, the blend partners and whether the nitrogen is wanted.
Can MAP and DAP be blended with urea?
MAP can. DAP cannot be stored blended with urea: the pair releases ammonia, loses nitrogen and cakes. Where a compound has to contain both nitrogen and phosphate, that single fact usually decides the specification.
Which is cheaper per unit of P2O5?
It varies with the market, and that is the point — the relationship is not fixed. Compare the delivered cost per tonne of P2O5 rather than the price per tonne of product, and include the nitrogen value in DAP if you are not going to use it.
Need a price for a specific cargo?
Give us the product, grade, quantity and discharge port, and the quotation comes back with the specification basis stated.