# Ammonium

> Ammonium (NH4+) is the positively charged form of nitrogen; a small share stabilises root-zone pH, but too much reduces cannabis yield and quality.

- Canonical: https://genetixbay.com/knowledge/glossary/ammonium.html
- Also written: NH4+, NH4, ammoniacal nitrogen, NH4-N, ammonium nitrogen
- 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"

Ammonium is the cation NH4+, a form of nitrogen plants can absorb directly and use without first reducing it. Its uptake releases hydrogen ions from the root, so it acidifies the [root zone](https://genetixbay.com/knowledge/glossary/root-zone.md). Inside the plant it must be assimilated quickly, because free ammonium is toxic at high levels.

## In practice

Mineral feeds usually keep ammonium to a small fraction of total N, often around 10-20% or less. That share offsets the upward [pH drift](https://genetixbay.com/knowledge/glossary/ph-drift.md) caused by [nitrate](https://genetixbay.com/knowledge/glossary/nitrate.md) uptake. Saloner and Bernstein found that high NH4/NO3 ratios reduced [cannabinoids](https://genetixbay.com/knowledge/glossary/cannabinoid.md), terpenoids and yield in [medical cannabis](https://genetixbay.com/knowledge/glossary/medical-vs-adult-use.md). Ammonium excess shows as dark, cupped or [clawed leaves](https://genetixbay.com/knowledge/glossary/leaf-clawing.md) and poor root growth, and it competes with calcium, magnesium and potassium uptake.

## Units and formula

[Lab reports](https://genetixbay.com/knowledge/glossary/coa.md) may give NH4-N (nitrogen only): 1 mg/L NH4-N = 1.29 mg/L NH4+.

## Don't confuse with

- **Ammonia (NH3)**: the uncharged gas, more toxic, favoured at high [pH](https://genetixbay.com/knowledge/glossary/ph.md).
- **Nitrate**: the main hydro N form, which pushes pH up.
- **Urea**: an organic N compound converted to ammonium by an enzyme.

## Related terms

[Nitrogen](https://genetixbay.com/knowledge/glossary/nitrogen.md), [Nitrate](https://genetixbay.com/knowledge/glossary/nitrate.md), [Monoammonium phosphate](https://genetixbay.com/knowledge/glossary/monoammonium-phosphate.md), [Ammonium nitrate](https://genetixbay.com/knowledge/glossary/ammonium-nitrate.md), [Urea](https://genetixbay.com/knowledge/glossary/urea.md)

## Read more

- [Nitrogen (N) in cannabis: nitrate vs ammonium, deficiency, toxicity and targets](https://genetixbay.com/knowledge/nutrients/nitrogen.md)
- [pH drift in hydro: why reservoir pH rises (and sometimes falls)](https://genetixbay.com/knowledge/ph-ec/ph-drift-hydro.md)

## Sources

1. 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
2. Langenfeld NJ, Bugbee B. 2025. pH control in recirculating hydroponics with nitric acid and ammonium nitrate. HortScience 60(9):1555. https://journals.ashs.org/view/journals/hortsci/60/9/article-p1555.xml