# Monoammonium phosphate

> Monoammonium phosphate (MAP, NH4H2PO4) supplies about 12% nitrogen as ammonium and 26.6% phosphorus, adding P while gently acidifying the root zone.

- Canonical: https://genetixbay.com/knowledge/glossary/monoammonium-phosphate.html
- Also written: MAP, NH4H2PO4, ammonium dihydrogen phosphate, 12-61-0, mono ammonium phosphate
- Glossary category: Nutrients · Evidence: Established
- Status: Draft: awaiting expert review · Updated: 2026-10-31
- Licence: CC BY-SA 4.0 (https://creativecommons.org/licenses/by-sa/4.0/), attribute "GenetixBay cannabis glossary"

Monoammonium phosphate is the salt NH4H2PO4. Soluble technical grade is sold as 12-61-0, which works out to about 12% N, all [ammonium](https://genetixbay.com/knowledge/glossary/ammonium.md), and 26.6% elemental P. Cheaper granular agricultural MAP often contains insoluble impurities and is not suitable for hydro.

## In practice

MAP is used where a grower wants phosphorus plus a little ammonium to steady [pH drift](https://genetixbay.com/knowledge/glossary/ph-drift.md) in [recirculating systems](https://genetixbay.com/knowledge/glossary/recirculating-system.md). It also adds nitrogen, so it does not suit a late-flower feed where N is being tapered; [MKP](https://genetixbay.com/knowledge/glossary/monopotassium-phosphate.md) is the better P source there. Keep total ammonium to a small share of total N, as high NH4/[NO3](https://genetixbay.com/knowledge/glossary/nitrate.md) ratios cut cannabis yield and [cannabinoids](https://genetixbay.com/knowledge/glossary/cannabinoid.md).

## Units and formula

1 g/L gives about 120 mg/L (ppm) N and 266 mg/L P.

## Don't confuse with

- **Diammonium phosphate (DAP)**: (NH4)2HPO4, more ammonium and more alkaline.
- **Monopotassium phosphate (MKP)**: P with potassium instead of ammonium.
- **MAP as a shipping acronym**: modified-atmosphere packaging is unrelated.

## Related terms

[Phosphorus](https://genetixbay.com/knowledge/glossary/phosphorus.md), [Ammonium](https://genetixbay.com/knowledge/glossary/ammonium.md), [Phosphate](https://genetixbay.com/knowledge/glossary/phosphate.md), [Monopotassium phosphate](https://genetixbay.com/knowledge/glossary/monopotassium-phosphate.md), [Nitrogen](https://genetixbay.com/knowledge/glossary/nitrogen.md)

## Read more

- [Hydroponic salts explained: what each fertiliser salt supplies](https://genetixbay.com/knowledge/nutrients/hydroponic-salts.md)

## Sources

1. Sonneveld C, Voogt W. 2009. Plant Nutrition of Greenhouse Crops. Springer. https://doi.org/10.1007/978-90-481-2532-6
2. Saloner A, Bernstein N. 2022. Nitrogen source matters: high NH4/NO3 ratio reduces cannabinoids, terpenoids, and yield in medical cannabis. Frontiers in Plant Science 13:830224. https://doi.org/10.3389/fpls.2022.830224