Monoammonium Phosphate (MAP) — Frequently Asked Questions

Because it dissolves to a mildly acidic solution, around pH 4.5. On high-pH soils phosphorus reacts with calcium to form insoluble compounds and becomes unavailable to the plant. The acidic reaction zone around a dissolving MAP granule counteracts that locally, keeping phosphorus soluble and available to the root for longer than an alkaline source would.

It works on all three common fire classes, which is what ABC rating means. On class A solid fires it melts and flows over the burning material to form a barrier layer that excludes oxygen. On class B and C fires it decomposes endothermically, absorbing heat and interrupting the free-radical chain reactions that sustain the flame.

11-52-0, meaning 11 percent nitrogen, 52 percent phosphorus expressed as P2O5 and no potassium. That phosphorus content is the highest of any widely traded straight phosphate fertiliser, which reduces freight and handling cost per unit of nutrient delivered.

Generally yes. DAP dissolves to an alkaline solution and can release free ammonia around the granule, which damages germinating seedlings if placed in direct contact with seed. MAP's mildly acidic reaction does not produce that effect, so it is the usual choice where fertiliser is banded with or close to the seed.