Magnesium doesn’t always get the attention of nitrogen, phosphorus, or potassium, yet it quietly drives some of the most important processes in plant health. From powering photosynthesis to enabling protein synthesis, magnesium underpins both yield and resilience.
In regenerative farming, getting magnesium right is one of the simplest and most cost-effective ways to boost crop performance. Soils may test high in magnesium, yet plants still show deficiency symptoms. The key lies in understanding how magnesium behaves in the plant, in the soil, and within the broader nutrient system.
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Magnesium in the Plant
Magnesium is one of the first minerals we correct when helping farmers transition into regenerative systems. While it often gets overlooked in favour of nitrogen, phosphorus, or potassium, magnesium is at the heart of plant function. Without it, photosynthesis and protein synthesis stall, two of the most important drivers of yield and quality.
Magnesium and Photosynthesis
The most critical role of magnesium is its central place in the chlorophyll molecule. Chlorophyll is the pigment responsible for capturing sunlight, the very first step in photosynthesis. Without magnesium, the molecule is incomplete and unable to harness light effectively.
Low magnesium means fewer chlorophyll molecules, reduced photosynthesis, and ultimately less sugar production. On a sap test, this shows up as low brix readings (below 12). Boosting magnesium is often one of the cheapest and fastest ways to increase photosynthesis and sugar levels in plants.
Moving Sugars Where They’re Needed
Magnesium also attaches to ATP, the “energy battery” in plants. This powers proton pumps that enable sugar transport through the phloem. When magnesium is deficient, sugars accumulate in the leaves instead of moving to roots, fruits, and developing tissues. The result: stunted root growth, smaller grain size, and uneven energy distribution across the plant.
In fact, research shows magnesium-sufficient plants distribute sugars evenly, while deficient plants trap sugars in older leaves. This starves growing tissues of energy, limiting yield potential.
From Nitrogen to Protein
Another vital role of magnesium is in protein synthesis. Through the enzyme glutamine synthetase, magnesium helps convert ammonium into amino acids. Without it, ammonium accumulates, leading to imbalances that attract pests and diseases.
Magnesium also stabilises ribosomes, the structures that link amino acids into complete proteins. Without enough magnesium, plants struggle to convert nitrogen into protein, resulting in high levels of nitrates or ammonium in sap tests and reduced nutritional quality.
Signs of Magnesium Deficiency
Because magnesium is mobile in the plant, it moves from older leaves to younger ones during shortages. This creates a characteristic pattern: yellowing between the veins of older leaves while the veins remain green. Other symptoms include:
Low brix levels (poor photosynthesis)
Stunted roots due to poor sugar transport
Ammonium buildup on sap tests
Smaller grain size and reduced protein content in crops like wheat
Why Magnesium Matters in Regenerative Systems
Getting magnesium right addresses both photosynthetic efficiency (the plant’s energy engine) and protein synthesis (its building blocks). Together, these functions underpin plant resilience, yield, and pest resistance.
In regenerative farming, managing magnesium effectively ensures carbon capture, nutrient cycling, and plant health all work in sync. It’s one of the simplest yet most powerful levers farmers can use to set their crops up for success.
Magnesium in the Soil
Many Australian soils hold abundant magnesium, yet crops can still show deficiency symptoms. This can be due to many reasons but is usually either due to a soil deficiency or minerals interactioning with magnesium to inhibit uptake. To better understand mangesium in the plant, we need to understand magnesium in the soil.
The Forms of Magnesium in Soil
Magnesium exists in several pools, each with a different level of availability to plants:
Mineral Magnesium – locked in rock minerals (e.g., basalts), slowly released over time.
Non-exchangeable Magnesium – trapped between clay layers, not immediately available.
Exchangeable Magnesium – held on the soil colloids (clays and organic matter), available for plant uptake.
Soluble Magnesium – dissolved in soil water, directly accessible to roots.
Plants draw magnesium from the soluble and exchangeable pools. These are continually replenished by the breakdown of mineral and non-exchangeable forms.
Soil Type Matters
Magnesium issues show up most often on light sandy soils, where reserves are low and leaching is common. In contrast, heavy clay soils typically contain large reserves of magnesium, making true deficiencies less likely.
On clays, problems arise not from a lack of magnesium, but from competition with other cations such as calcium, potassium, sodium, or ammonium, which can block uptake.
Antagonisms That Limit Uptake
Magnesium is easily suppressed by other nutrients, particularly:
Ammonium (NH₄⁺): Excess ammonium fertilisers and manures can block magnesium uptake, causing sugar accumulation in leaves and a build-up of ammonium in plant sap, conditions that attract pests.
Potassium (K⁺): Heavy potassium inputs compete with magnesium for uptake sites.
Calcium (Ca²⁺): High lime or gypsum applications can displace magnesium.
Sodium (Na⁺): Sodic soils exacerbate antagonism, further reducing magnesium availability.
This explains why plants can suffer magnesium deficiency even when soil tests show high reserves.
Soil Test Targets
When reviewing soil test results, typical target ranges for magnesium are:
Sandy soils: ~25 ppm soluble Mg, 75 ppm exchangeable Mg.
Clay soils: up to 160 ppm soluble Mg and 290 ppm exchangeable Mg.
Total Mg: Ideally above 500 ppm (a lower threshold).
For base saturation, magnesium should make up around 20% of the cation exchange capacity (CEC) on sands and about 12% on clays.
Fertiliser Options for Magnesium
Magnesium (Mg) is often one of the first nutrients corrected in a regenerative fertility program due to it’s importantance in both photosynthesis and protein synthesis. While soils may hold large reserves, plant deficiencies are common because of antagonisms with other cations (like potassium, calcium, sodium, and ammonium). Fertiliser choice matters a lot for whether magnesium ends up in the crop where it’s needed most.
Soil-Applied Options
Dolomite
A natural source of both calcium carbonate and magnesium carbonate.
Best suited for sandy or acidic soils where total magnesium is low.
Corrects soil pH while supplying magnesium.
Most effective when soil pH is below 6, as magnesium availability drops in both acidic (<6) and alkaline (>7) conditions.
Foliar Options
Magnesium Sulphate (Epsom Salt, Kieserite)
Highly soluble and plant-available.
Suitable for both soil and foliar applications.
Often used where magnesium is present in the soil but uptake is blocked by antagonisms.
Magnesium Nitrate
Provides magnesium alongside nitrate nitrogen.
Useful if additional nitrogen is required, but the nitrate form can increase pest pressure if overused.
Often less preferred in regenerative systems compared to magnesium sulphate.
Avoid Magnesium Chloride
Though it supplies magnesium, the chloride ion risks leaf burn and other negative effects.
Generally unsuitable for foliar use.
Foliar Magnesium
When soils are already high in magnesium but plants still show deficiency, foliar feeding is often the best solution. Foliar sprays bypass soil antagonisms and deliver magnesium directly to the leaf where it supports chlorophyll formation, sugar transport, and protein synthesis.
The most effective choice is magnesium sulphate, which is affordable, easy to mix, and safe when buffered correctly. For extra efficiency, it can be combined with fulvic acid to enhance uptake.
Managing Magnesium Regeneratively
Step 1: Check Your Soil
The first question is simple: do you have enough magnesium in the soil?
Sandy soils often lack total magnesium reserves. Here, applying dolomite can both supply magnesium and correct pH, which strongly affects availability (Mg is less available below pH 6 or above pH 7).
Clay soils usually contain abundant magnesium, so deficiencies are less about shortages and more about uptake problems caused by nutrient antagonisms (e.g., high ammonium, potassium, calcium, or sodium).
Step 2: Use Sap Tests for Insight
Regenerative farmers know soil tests don’t tell the whole story. Differential sap tests show how nutrients are moving through the plant:
If older leaves test lower than younger ones, magnesium is being reallocated, a sign of deficiency.
High ammonium levels in sap often go hand-in-hand with magnesium shortages, since the plant can’t convert ammonium into amino acids without sufficient Mg.
This makes sap testing a powerful tool for catching imbalances before they limit photosynthesis or protein synthesis.
Step 3: Foliar Magnesium
When soils contain plenty of magnesium but uptake is blocked, foliar applications are the fastest fix. They bypass soil chemistry and deliver magnesium directly where it’s needed.
Magnesium sulphate (Epsom salts) is the preferred choice.
Mixing with fulvic acid can improve uptake.
Avoid magnesium chloride, which risks leaf burn.
Foliar feeding is especially valuable during critical growth stages when demand is high.
Step 4: Support Biology
Regenerative management doesn’t stop at chemistry. Biology matters too:
Mycorrhizal fungi enhance magnesium uptake, helping plants access pools that would otherwise remain locked away.
Other beneficial microbes solubilise mineral magnesium, making it more available to the crop.
By fostering soil biology through practices like reducing fungicides, maintaining living roots, and avoiding excess salts, we can naturally increase magnesium efficiency.
Step 5: Keep the System in Balance
Magnesium doesn’t work in isolation. Too much focus on one nutrient can create new problems. For example:
Excess magnesium can suppress manganese uptake, reducing disease resistance.
High ammonium fertilisers increase magnesium demand but simultaneously block its uptake.
Regenerative nutrient management means viewing magnesium as part of the whole system, not just chasing numbers on a test.
The Takeaway
Managing magnesium regeneratively comes down to:
Checking total reserves (soil tests).
Confirming uptake (sap tests).
Applying the right fertiliser in the right way (dolomite on sands, foliar Mg on clays).
Supporting biology for long-term efficiency.
When done well, magnesium management boosts photosynthesis, protein synthesis, and plant resilience—helping crops thrive without the cycle of deficiency, pests, and inputs.
Conclusion
Magnesium may not always be the first nutrient on a farmer’s mind, but it should be. From its central role in chlorophyll to its function in protein synthesis, magnesium influences photosynthesis, energy flow, and plant resilience more than most realise.
In the soil, magnesium supply depends on both reserves and balance with other cations. In the plant, deficiency shows up in sugar blockages, poor protein formation, and increased pest pressure. The solution isn’t to apply more indiscriminately, but to manage magnesium regeneratively: testing soils and sap, applying the right fertiliser in the right form, and supporting the biology that helps unlock it.
When magnesium is managed well, crops capture more carbon, convert nitrogen into true protein, and resist pest and disease pressure naturally. It’s a clear example of how smart, regenerative nutrition management builds both productivity and resilience, laying the foundation for healthier soils, stronger plants, and more profitable farming systems.
