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Nutrition

Mulder's chart

Mulder's chart is the nutrient wheel that gets reposted on every grow forum. Lines between nutrients say which ones block or help each other. This guide redraws it with a source behind each line, or dashed lines where there is none, and says where each line holds. Most of them only matter when one nutrient is far over target, and the original chart is lacking a lot of truths.

Updated October 2026 14 min read By Connor Schmitz

Origin

The chart is credited to D. Mulder and a 1953 paper called Les éléments mineurs en culture fruitière, French for "minor elements in fruit growing." It was given at a national fruit growing conference in Saint-Vincent, Italy. Papers that cite it don't agree on the page numbers.

The paper isn't online. Two BYU researchers posted an English machine translation, but the record is now marked withdrawn. The title says fruit growing, which means orchard trees in soil. It wasn't about hydroponics.

The chart also doesn't say how much. A line between two nutrients doesn't tell you how big the effect is, or at what level it starts. The lines below are the version most often reposted, as listed on Mosaic's Crop Nutrition site.

A map, not a diagnosis

A line on the chart is a reason to check, not a reason to change your feed. Get a soil, tissue or water test before you add one nutrient to fix another.

The wheel

Try it

Tap a nutrient to see its lines

Twelve nutrients in a circle, joined by 32 lines. Solid lines have a source; dashed lines don't. Terracotta lines block, green lines help. Calcium has the most sourced lines, most of them about soil pH. N P K Ca Mg S Fe Mn Zn Cu B Mo
Blocks Helps No source

Tap a nutrient to see each of its lines and what backs it up. Every line is also listed under Every line.

The reposted chart has 31 lines, and 28 have a source. Three of those point the other way, so they're drawn as blocks. Ammonium against calcium is sourced but not on the chart, so it's drawn here too.

Of the 28 sourced lines, 5 are really about soil pH and 2 are reactions in a concentrated stock tank, not in the plant. Several more only show up where the soil is already short of one nutrient, or where the other is at a toxic level. Three point the wrong way. The chart says nitrogen helps magnesium, and Wisconsin Extension says ammonium on sandy soil makes magnesium deficiency worse. It also says potassium helps manganese and copper helps molybdenum. In plants, both pairs work against each other.

Mechanisms

When a line holds up, it's for one of five reasons. Knowing which one tells you whether it applies to your setup.

At the root K, Mg, Ca Similar ions compete to get in. Potassium, magnesium, calcium and ammonium crowd each other out. So do iron and manganese, which are close in size.
In the tank Ca + SO4 At stock strength, calcium with sulfate or phosphate forms a solid that settles out and clogs emitters. Nothing to do with the plant.
In the soil P Phosphate binds to iron and aluminum in acid soil and to calcium in alkaline soil.
Soil pH Lime Liming raises pH, and zinc, iron, manganese, boron and copper all get less available. The chart blames calcium. The cause is the pH.
In the plant S, Mo Sulfur and molybdenum are both needed to process nitrate. Short on either, the plant looks short on nitrogen.

Excess

Most of these lines need one nutrient to be well over what the plant needs. A few examples from the sources:

  • Potassium and magnesium: Wisconsin says the problem usually doesn't happen when the soil holds more exchangeable magnesium than potassium.
  • Calcium and magnesium: Wisconsin found Ca:Mg ratios from 1:1 to 8:1 all grow normal crops, as long as neither is short. It calls claims about "balancing" the ratio unsubstantiated.
  • Phosphorus and zinc: the risk is mainly where soil zinc is already low. Wisconsin's advice is to avoid overusing phosphorus there.
  • Copper and iron: the tomato trial that showed it used 3 to 22 ppm copper in the nutrient solution.
  • Manganese and iron: manganese toxicity is common in acid soils below pH 5.5.

So when a deficiency shows up, look at what's high as well as what's low. If heavy potash brought on a magnesium shortage, Wisconsin names Epsom salt as the best source.

Soil or hydro

Much of the chart is soil chemistry. The pH lines and the phosphate binding lines come from what happens in soil. In a soilless mix or hydro system where you set the feed and its pH, those mostly turn into one rule: keep the feed pH where it belongs. The pH Adjustment Calculator helps there.

The root lines still apply in hydro, because they happen at the root. And the tank lines only apply where there's a stock tank. They're also the ones most likely to bite. Penn State's recipe puts the calcium nitrate in one tank and the potassium phosphate and sulfates in the other.

Your water counts too

Hard water already brings calcium, and sometimes sulfate, into the tank. Labs report sulfate as S or as SO4, and SO4 is 3 times the S number, so check which one yours uses. The water test guide covers reading those lines.

Quick check

Your A tank holds calcium nitrate at stock strength. Where should the Epsom salt (magnesium sulfate) go?

Answer: in B. At stock strength, calcium and sulfate form gypsum, which settles out and clogs emitters. Penn State's recipe keeps magnesium sulfate with the phosphate, in the tank without calcium.

Fertigation Calculator Builds a feed from your fertilizers and water test, and splits it across your injector's stock tanks with calcium kept away from sulfate and phosphate.
Open the calculator

Calcium

Three lines on the wheel cut calcium uptake: potassium, magnesium and ammonium. They're real, but they're rarely the whole story behind blossom-end rot or tipburn.

Calcium moves through the plant in the water flowing from the roots to the leaves, so it goes where the water goes. When vapor pressure deficit (VPD) is high, leaves transpire hard and pull the calcium to themselves, and fruit gets less. In a 1993 tomato study by Adams and Ho, more humid days sent more calcium to the young fruit. Check VPD and watering before blaming the potash. The VPD guide and the foliar feeding guide cover this in more detail.

Quick check

New leaves on a pH 7.8 soil are yellow between the veins. The chart has a line from calcium to iron. What's the likely cause?

Answer: the pH. Wisconsin says iron in the soil solution falls sharply as pH rises, and bicarbonate in alkaline soil ties up iron inside the plant. The calcium line on the chart is really a lime line.

Every line

Each line on the wheel, where it holds, and the source. Lines with no source are kept so you can see what the chart claims and nobody has backed up.

N × K At the root Ammonium only. Ammonium is a positive ion like potassium and competes with it at the root, until soil bacteria turn it into nitrate. Feeding the nitrogen as potassium nitrate or calcium nitrate avoids it. Delaware.
N × B At the root In a glasshouse study on sainfoin, a forage legume, adding nitrogen lowered boron concentration and uptake in the shoots and roots. It is one study, a master's thesis. Juan 1982.
N × Cu In the plant On copper-poor soil, nitrogen made wheat grow so much faster that its copper was spread thin, and the plants showed copper deficiency by harvest. Adding zinc made it worse. Chaudhry and Loneragan 1970, Hill 1978.
P × K No source The chart says phosphorus and potassium block each other. No source for this one. A 2017 Montana State study notes that the levels where they interfere aren't well documented. Kibiwott and Burgess 2017.
P × Ca In the tank In a concentrated stock tank, calcium and phosphate form a solid that settles out and clogs drip emitters. In neutral and alkaline soil, phosphate binds to calcium compounds, so here it is mostly calcium locking up phosphorus. Penn State, Wisconsin A2520.
P × Zn In the soil Heavy phosphorus can bring on zinc deficiency, mainly where soil zinc is already low. Phosphorus may make zinc insoluble in the soil or at the root, or interfere with it inside the plant. Wisconsin A2528.
P × Fe In the soil In acid soil, phosphate reacts with iron compounds and becomes insoluble. That is iron locking up phosphorus, not phosphorus starving the plant of iron. Wisconsin A2520.
P × Cu At the root On sand short of copper, more phosphorus brought on copper deficiency in clover. Bigger plants spread the copper thin, and phosphorus also cut how much copper the roots took up. Reuter 1981.
K × Ca At the root Very high potash rates cut calcium uptake. Wisconsin's example is potatoes. Calcium in fruit also depends on VPD and transpiration. Wisconsin A2523, Delaware.
K × Mg At the root High potassium (or ammonium) rates on sandy soil often make magnesium deficiency worse. Wisconsin says it usually doesn't happen when the soil holds more magnesium than potassium. Wisconsin A2524.
K × B At the root Only shown where boron is already too high. In pepper, added potassium lowered boron in the shoots and eased boron toxicity. Samet 2015.
S × Ca In the tank In a concentrated stock tank, calcium and sulfate form gypsum, a solid that settles out. Keep calcium in a different tank from sulfates. Penn State.
S × Cu No source The chart says sulfur and copper block each other. No source for this one.
S × Mo At the root High sulfate can suppress molybdenum uptake, possibly because sulfate and molybdate are similar ions. A 2020 cabbage study found no direct competition, so this one isn't settled. Wisconsin A3555, Zuidersma 2020.
Ca × Mg At the root Excess magnesium can cut calcium and potassium uptake. The other way round, Wisconsin found Ca:Mg ratios from 1:1 to 8:1 all grow normal crops, as long as neither is short. Delaware, Wisconsin A2523.
Ca × Zn Soil pH Overliming, especially on sand, can bring on zinc deficiency. Zinc gets less soluble as pH rises. It's the pH, not the calcium. Wisconsin A2528.
Ca × Fe Soil pH Iron in the soil solution falls sharply as pH rises, and bicarbonate in alkaline soil ties up iron inside the plant. A lime problem, not a calcium one. Wisconsin A3554.
Ca × Mn Soil pH Manganese in solution drops about 100 times for each unit the pH rises. Deficiency is most common above pH 6.5. Wisconsin A2526.
Ca × B Soil pH Soils at pH 7 or above are more likely short on boron. Wisconsin's advice is not to lime above pH 6.8. Wisconsin A2522.
Fe × Mn At the root Iron and manganese ions are close in size and share transporters. Too much manganese, common in acid soil below pH 5.5, causes iron deficiency, and added iron reverses it. Li 2026, Wisconsin A2526.
Fe × Cu At the root In a hydroponic tomato trial, 3 to 22 ppm copper cut iron uptake and its movement to the leaves, and the leaves yellowed. Martins 2006.
Fe × Zn In the plant Too much zinc yellows the leaves like iron deficiency, and more iron in the feed mostly fixes it. In hydroponic corn the leaves had normal iron, so zinc gets in the way of using it. Rosen 1977, Fontes and Cox 1998.
Cu × Mn No source The chart says copper and manganese block each other. The studies on this pair are on algae, not crop plants.
N × Ca Not on chart Not on the chart. Ammonium competes with calcium at the root, the same way it does with potassium. Delaware.
N × Mg Backwards The chart draws this as helping. For ammonium on sandy soil, Wisconsin says the opposite: high rates often make magnesium deficiency worse. Wisconsin A2524.
N + S In the plant Sulfur is part of the enzyme a plant uses to process nitrate, so a plant short on sulfur can't use its nitrogen and looks nitrogen deficient. Wisconsin A2525.
N + Mo In the plant Molybdenum is needed to turn nitrate into organic nitrogen, and for legumes to fix nitrogen. The first sign of molybdenum deficiency looks like nitrogen deficiency. Wisconsin A3555.
P + Mg In the plant In Swedish wheat fields, yield tracked the ratio of magnesium to phosphorus in the crop. Magnesium was the limit at lower yields and phosphorus at higher ones. Weih 2021.
K + Fe At the root Only where manganese is too high. In hydroponic barley, extra potassium kept manganese out and the leaves got their iron back. Potassium didn't change iron uptake on its own. Alam 2002, Alam 2005.
K × Mn Backwards The chart draws this as helping. In hydroponic barley and rice, extra potassium cut manganese uptake. That helps when manganese is toxic. Alam 2003, Alam 2005.
S + Mn Soil pH Elemental sulfur turns to acid in the soil, which lowers pH and frees up manganese. Sulfate had no effect in the same trial, so sulfate fertilizers don't do this. Garey and Barber 1952.
Cu × Mo Backwards The chart draws this as helping. In plants the two work against each other: more molybdenum, less copper, in a long-term Hungarian field trial and in a greenhouse grass study. Puskás-Preszner 2011, de Iorio 1998.
Soil Test Calculator Reads your soil test and gives lime and fertilizer rates, so you can see what's high before blaming an interaction.
Open the calculator

Summary

  • Mulder's chart comes from a 1953 paper on fruit growing. It shows which nutrients interact, not how much or at what level.
  • 28 of its 31 lines have a source. Three of those say the chart has it backwards. The other 3 are dashed.
  • Most lines need a real excess. Look at what's high, not only what's low.
  • Many calcium lines are about lime and soil pH. In hydro, the stock tank lines matter more.
  • Calcium shortages in fruit and leaf tips follow VPD and transpiration as much as the feed.

Sources

University extension and peer-reviewed research. The chart's own line list is from a fertilizer company page and is cited only as the version being checked.

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