Understanding magnesium’s role in crop production

This article explores magnesium’s role as a secondary macronutrient, how to identify and correct deficiencies, its interaction with other nutrients, and how to effectively supply it through micronized calcium magnesium carbonate.

The Role of magnesium in crops 

Magnesium is the central atom in chlorophyll, making it indispensable for photosynthesis. Beyond this, magnesium activates over 300 enzymes involved in chlorophyll formation, carbohydrate transport, enzyme activation, and lipid metabolism.

It helps to regulate the movement of carbohydrates and sugars from leaves to roots and fruits, directly influencing yield and quality. During grain and fruit development, magnesium supports sugar transport and starch formation. 

Crop demand and estimated magnesium uptake by crop

 All plants require magnesium, but the amount needed varies among crops and growth stages, with typical requirements ranging from 15 to 70 kg per hectare. For example, high-demand crops such as sugarcane, potatoes, coffee, and banana may require between 30 and 60 kg of magnesium per hectare, while moderate-demand crops like corn, wheat, and soybeans typically need between 15 and 40 kg per hectare. Additionally, some crops—including soybean, oilseed rape, potato, coffee, citrus, and banana—are particularly sensitive to magnesium deficiency and may show symptoms more readily if their needs are not met.

Magnesium in soils: availability and influencing factors

Magnesium in soil exists in several forms: as exchangeable magnesium, bound to clay minerals, and dissolved in the soil solution. Its availability to crops is influenced by multiple factors. High levels of calcium, potassium, or ammonium can reduce magnesium uptake due to competition at the root interface. Soil texture also plays a role—sandy soils tend to retain less magnesium, while clay soils hold more but may bind it tightly, making it less available to plants. Magnesium availability decreases in acidic soils (pH below 5.5), especially when aluminum and hydrogen ions dominate the exchange sites. Heavy rainfall or irrigation can leach magnesium from the root zone, and high nitrogen fertilization can promote rapid plant growth, diluting magnesium concentration in plant tissues. Additionally, cold and waterlogged soils reduce root activity and nutrient uptake. Therefore, a comprehensive soil test is essential to assess both pH and exchangeable magnesium levels, providing the foundation for effective magnesium fertilization recommendations.

Tips for checking magnesium sufficiency in soils and crops

• ^{Soil test: Measure exchangeable Mg (cmol/kg or mg/kg). Target 0.5–2.0 cmol/kg (60–200 mg/kg available Mg) in the root zone according to crop. Fruit trees like citrus, banana and coffee require ≥80 – 120 mg/kg, legumes ≥50-70mg/kg; cereals ≥50mg/kg. Assess magnesium saturation and aim for 10-20% in the Cation Exchange Capacity (CEC) to be magnesium.}
• ^{Tissue test: Collect mature leaves and ensure magnesium levels are within 0.15–0.80% Mg on a dry weight basis, depending on the crop.}

Using micronized dolomite for suppling magnesium

Micronized calcium magnesium carbonate (CaMg(CO₃)₂), also known as dolomite, is a naturally occurring mineral that provides three benefits to the crop. It is a source of both magnesium and calcium nutrition and is also ideal for correcting acidic soils. When finely micronized and granulated it provides a fast reactivity and nutrient availability combined with flexible application time to meet farmer needs 

Application tips:

• Pre-planting: 2-4 weeks before sowing or transplanting to allow for soil pH adjustment. Ideal for crops sensitive to soil acidity.
• At planting or after planting: Ideal for providing Mg nutrition as required by the crop.
• Post harvest: Apply after crop harvest to prepare soil for next season. Helps restore Ca and Mg levels and adjusts pH for following crops.
• During soil preparation: Incorporate into soil during tillage and plowing to distribute nutrients and correct soil pH.
• In perennial systems: Apply during dormant season (late fall or early spring), around the base of the orchards or vines.

Final thoughts

Magnesium is far more than a supporting nutrient—it is fundamental to plant energy production, enzyme activation, and the movement of sugars that drive yield and quality. By understanding the specific magnesium needs of each crop and recognizing the factors that influence its availability, growers can prevent hidden deficiencies and optimize plant health. Regular soil and tissue testing, combined with timely and appropriate magnesium applications, should be central to every crop nutrition program. Proactive magnesium management not only supports robust growth and resilience but also helps unlock the full potential of your fields. For more information about Omya Magprill – here.