# Nutrient antagonism and Mulder's chart: what the evidence actually says

> Mulder's chart is a mid-20th-century wheel of nutrient interactions. It is a useful reminder that excess of one nutrient can suppress another, but it is a teaching sketch, not a quantitative tool. A review of 117 published interactions found synergy far more often than antagonism; the antagonisms that reliably matter in practice are among cations (K, Ca, Mg, NH4, Na), phosphorus with zinc and iron, and iron with manganese.

- Canonical: https://genetixbay.com/knowledge/nutrients/nutrient-antagonism.html
- Category: Nutrients · Level: Intermediate
- Evidence: Supported · Status: Draft: awaiting expert review (some figures are being checked)
- Stage: Any stage · Systems: Any system
- Updated: 2026-10-31 · Licence: CC BY-SA 4.0 (https://creativecommons.org/licenses/by-sa/4.0/), attribute "GenetixBay Knowledge Base (genetixbay.com/knowledge)"

## Questions and answers

**What is Mulder's chart?** Mulder's chart is a circular diagram, attributed to the Dutch soil scientist D. Mulder in the early 1950s, showing which plant nutrients suppress or help each other. It is a useful teaching sketch that reminds growers excess of one nutrient can cause shortage of another, but it has no doses and is not a quantitative tool for adjusting a cannabis feed.

**Does too much potassium lock out magnesium?** Yes, too much potassium can suppress magnesium and calcium uptake through cation competition at the root, an established effect in plant nutrition that has also been observed in cannabis. A standard Hoagland-type solution runs about 235 mg/L potassium, 200 mg/L calcium and 49 mg/L magnesium; antagonism bites when potassium climbs far above calcium, as happens when PK boosters are stacked.

**What is nutrient lockout and is it real?** Nutrient lockout is real in a narrow sense, but most cases growers call lockout are actually root-zone pH or root failures. Genuine antagonism mostly involves competing cations, phosphorus with zinc and iron, and iron with [manganese](https://genetixbay.com/knowledge/glossary/manganese.md). Fix pH before any lockout theory, confirm with runoff EC or a lab test, and flush only for real [salt build-up](https://genetixbay.com/knowledge/glossary/salt-build-up.md).

**Which nutrients compete with each other?** The nutrient competitions that reliably matter are among cations, where potassium, [ammonium](https://genetixbay.com/knowledge/glossary/ammonium.md) and sodium suppress calcium and magnesium and calcium suppresses magnesium, plus phosphorus with zinc and iron, iron with manganese, and copper and zinc with iron. A review of 117 published interactions found synergy more often than antagonism: 43 synergistic against 17 antagonistic.

**Can too much phosphorus cause zinc deficiency?** Excess phosphorus is associated with reduced zinc effectiveness and poorer iron movement in many crops, through precipitation and interference inside the plant. This is supported by general crop research but has not been tested in cannabis. Keeping solution phosphorus at moderate levels and not stacking [bloom boosters](https://genetixbay.com/knowledge/glossary/bloom-booster.md) avoids the risk.

**Short answer.** Mulder's chart is a circular diagram, attributed to the Dutch soil scientist D. Mulder in the early 1950s, showing which nutrients suppress (antagonise) or help (synergise) each other [7]. It is a good reminder that excess of one nutrient can cause shortage of another. But it is a teaching sketch, not a calculator. A review of 117 published interactions found synergy more often than antagonism; the antagonisms that reliably matter are among the cations (K, Ca, Mg, NH₄, Na), phosphorus with zinc and iron, and iron with manganese [1][6].

## What's happening

"Antagonism" covers several different mechanisms that the chart lumps together:

1. **Competition at root uptake.** Ions with similar charge compete for transporters and for the root's charge balance. K⁺, NH₄⁺ and Na⁺ suppress Ca²⁺ and Mg²⁺ uptake; Ca²⁺ suppresses Mg²⁺ [6]. In cannabis, higher K supply was linked to lower Ca and Mg uptake [3], and high ammonium reduced cation uptake and yield [4].
2. **Precipitation in the [root zone](https://genetixbay.com/knowledge/glossary/root-zone.md) or tank.** Ca with [phosphate](https://genetixbay.com/knowledge/glossary/phosphate.md) or sulfate; Fe with phosphate at high pH. That is chemistry, not physiology, and pH controls most of it (see [pH and availability](https://genetixbay.com/knowledge/ph-ec/ph-nutrient-availability.md)).
3. **Interference inside the plant.** High P is associated with reduced Zn effectiveness and Fe translocation in many crops [6]; Fe and Mn compete; Cu and Zn compete.
4. **Dilution.** Adding a growth-limiting nutrient makes the plant bigger, which lowers the *concentration* of others in tissue without any real antagonism. Shiponi and Bernstein saw P supply reshape the whole cannabis ionome, partly this way [5].

Rietra et al. reviewed 94 papers describing 117 interactions across all macro- and [micronutrients](https://genetixbay.com/knowledge/glossary/micronutrient.md): 43 were synergistic, 17 antagonistic, 35 zero-interaction, the rest non-significant or negative. Antagonistic effects on yield were found most often for divalent cations [1]. The authors also note that the number of studied interactions is low, which makes firm conclusions difficult [1].

## The interactions worth knowing

| Excess of | Can suppress | Mechanism | Strength of evidence |
|---|---|---|---|
| K | Mg, Ca | Cation competition | *Established* [6]; observed in cannabis [3] |
| NH₄⁺ | K, Ca, Mg | Cation competition, root damage | *Established* [6]; cannabis [4] |
| Ca | Mg, (K) | Cation competition | *Established* [6] |
| Na | K, Ca | Cation competition, membrane displacement | *Established* [6] |
| P | Zn, Fe, (Cu) | Precipitation and in-plant interference | *Supported* in crops [6]; untested in cannabis |
| Fe | Mn (and the reverse) | Uptake competition | *Supported* [6] |
| Cu, Zn | Fe | Competition | *Supported* [6] |
| N (adequate) | Most others improve | Synergy via growth | *Established* [1] |
| High bicarbonate/pH | Fe, Mn, Zn, Cu, B, P | Solubility, not antagonism | *Established*; see [pH and availability](https://genetixbay.com/knowledge/ph-ec/ph-nutrient-availability.md) |

## How to use this

1. **Keep ratios sensible.** A standard Hoagland-type solution runs roughly K 235, Ca 200, Mg 49 mg/L (K:Ca:Mg ≈ 1.2:1:0.25). Big departures from that, especially K far above Ca, are where antagonism bites.
2. **Fix pH before any "lockout" theory.** Most so-called lockout is pH or root-zone failure.
3. **Don't stack boosters.** A PK booster plus a bloom base plus [Cal-Mag](https://genetixbay.com/knowledge/glossary/cal-mag.md) can push K, P and Ca far beyond need.
4. **Confirm with numbers.** [Runoff EC](https://genetixbay.com/knowledge/glossary/runoff-ec.md), a lab solution test, or a [leaf tissue test](https://genetixbay.com/knowledge/glossary/tissue-test.md) beat reading a wheel.

## Common mistakes

- Treating Mulder's chart as quantitative. It has no doses.
- Calling every [deficiency](https://genetixbay.com/knowledge/glossary/nutrient-deficiency.md) "lockout" and flushing with plain water, which removes everything. A [root-zone flush](https://genetixbay.com/knowledge/glossary/root-zone-flush.md) is for real salt build-up (runoff EC far above input), done with a light solution in soilless media (see [the flush debate](https://genetixbay.com/knowledge/harvest-cure/flush-debate.md)).
- Ignoring dilution when reading tissue tests.

## Evidence

- Cation antagonism (K/NH₄/Na vs Ca/Mg): *Established* in plant nutrition [6], *Supported* in cannabis [3][4].
- Synergism being more common than antagonism in yield studies: *Supported* (one large review [1]).
- Mulder's chart as a diagnostic tool: *Grower practice*; origin details
- Fageria 2001 citation details

## Sources

1. Rietra RPJJ, Heinen M, Dimkpa CO, Bindraban PS. 2017. Effects of nutrient antagonism and synergism on yield and fertilizer use efficiency. Communications in Soil Science and Plant Analysis 48(16):1895-1920. https://hub.ifdc.org/handle/20.500.14297/2410
2. Fageria VD. 2001. Nutrient interactions in crop plants. Journal of Plant Nutrition 24(8):1269-1290. https://doi.org/10.1081/PLN-100106981
3. Saloner A, Sacks MM, Bernstein N. 2019. Response of medical cannabis genotypes to K supply under long photoperiod. Frontiers in Plant Science 10:1369. https://doi.org/10.3389/fpls.2019.01369
4. Saloner A, Bernstein N. 2022. Nitrogen source matters. Frontiers in Plant Science 13:830224. https://doi.org/10.3389/fpls.2022.830224
5. Shiponi S, Bernstein N. 2021. The highs and lows of P supply in medical cannabis: effects on cannabinoids, the ionome, and morpho-physiology. Frontiers in Plant Science 12:657323. https://doi.org/10.3389/fpls.2021.657323
6. Marschner P (ed.). 2012. Marschner's Mineral Nutrition of Higher Plants, 3rd ed. https://doi.org/10.1016/C2009-0-63043-9
7. ICL Growing Solutions. Interactions between plant nutrients: a deep understanding. https://icl-growingsolutions.com/agriculture/knowledge-hub/interactions-between-plant-nutrients-a-deep-understanding/