MAP fertilizer 11-52-0: the starter phosphate for difficult soil

MAP fertilizer carries the highest phosphate analysis of the common granular products, at around 11% nitrogen and 52% phosphorus as P2O5, CAS 7722-76-1. On paper that makes it a straight upgrade on DAP, and on price per tonne it usually is not: DAP is generally cheaper per unit of phosphate and outsells it comfortably. The reason MAP gets specified anyway comes down to one property that has nothing to do with the analysis. As it dissolves it turns the soil around it acidic, to a solution pH of about 4 to 4.5, where DAP turns alkaline. Four situations make that worth paying for.

1. Alkaline and calcareous soils

Above roughly pH 7.5, applied phosphate reacts with soil calcium and precipitates into forms a crop cannot use, sometimes within weeks. Rate increases do not solve it, because the extra phosphate follows the first lot out of solution. The acidic zone a MAP granule creates around itself holds phosphorus available for longer in exactly that ground. On chalky, limestone-derived and irrigated arid soils this is the difference between fertilising the crop and fertilising the soil chemistry.

2. It is the safer product beside seed

MAP releases no free ammonia as it dissolves, which is what makes DAP risky in direct contact with germinating seed. That makes MAP the standard choice for seed-placed starter applications, where the drill puts fertilizer and seed down the same boot. Safe rates still depend on row spacing, soil moisture and crop, and pulses and oilseeds are more sensitive than cereals, so get a rate against your actual drill configuration rather than working from a general figure.

3. Less nitrogen where you do not want nitrogen

At 11% against DAP’s 18%, MAP puts down noticeably less nitrogen for the same phosphate. That is a drawback when the starter nitrogen is useful and an advantage when it is not: on legumes fixing their own nitrogen, on fields already carrying residual nitrogen from a previous crop, or wherever an early nitrogen dose would push vegetative growth you did not want. It also means the nitrogen side of the programme can be planned independently rather than being partly set by the phosphate decision.

4. A soluble grade exists for fertigation

Water-soluble technical-grade MAP is a distinct product used in drip and pivot fertigation and in greenhouse nutrient schedules. It matters that this is not the same thing as the granular field grade: granular product contains insolubles that will block filters and emitters within a season. Name fertigation at enquiry stage and the soluble grade gets quoted, usually in 25kg bags rather than bulk. The PubChem record for monoammonium phosphate carries the identifiers for your specification file.

What MAP fertilizer does not fix

An acidic reaction around the granule is local and temporary. It does not lower field pH in any lasting way, and it is not a substitute for correcting a soil that is genuinely out of range. That is a job for elemental sulphur or an acidifying amendment applied on its own schedule. MAP also carries no potassium, so on soils testing low in exchangeable potassium it needs pairing with muriate of potash or a compound blend. Deciding it on the phosphate figure alone is how a field ends up short of something else.

Buying MAP fertilizer in bulk

GCS supplies MAP fertilizer at 11-52-0 in 50kg bags, one-tonne bulk bags or loose in bulk, with water-soluble technical grade available to order, alongside DAP, NPK compounds, urea, CAN, ammonium nitrate and muriate of potash across the bulk fertilizer range. Tell us the soil pH, the crop and whether the product is going through soil or through an injector. If you are still weighing the two phosphates, our note on DAP placement rules sets out the other side of the comparison.