Magnesium fertilizers: properties and applications

Magnesium fertilizers are a group of substances that provide plants with available magnesium — the central element of the chlorophyll molecule, without which photosynthesis is impossible. Magnesium deficiency often manifests on light sandy and acidic soils, as well as on soils with high potassium and calcium content, which compete with magnesium for uptake. Magnesium fertilizers are used for basic soil application and foliar feeding, ensuring normal plant development and high crop quality.

Chemical Nature and Range

The main representatives of magnesium fertilizers are magnesium sulfate (epsomite, MgSO₄·7H₂O) and kieserite (MgSO₄·H₂O). Epsomite contains about 13.7% MgO (or 16.1% MgO calculated on a dry basis) and is readily soluble in water. Kieserite contains about 27% MgO, is less soluble but has a prolonged effect. In addition to sulfate forms, magnesium-containing complex fertilizers (e.g., boron-magnesium fertilizer), dolomite flour and magnesite are used in agriculture. Industry produces magnesium fertilizers in fine-crystalline and granular forms, allowing them to be used both for preparing solutions and for direct soil application.

Regulatory Framework

Requirements for magnesium sulfate as a reagent and fertilizer in Russia and CIS countries are regulated by GOST 4523-77 (magnesium sulfate heptahydrate). For kieserite and other forms, manufacturers' technical specifications apply. Depending on the application, products are produced in various grades and classes. For agricultural use, compliance with sanitary and hygienic standards for heavy metal impurity content is important.

Agronomic Value and Applications

Magnesium activates more than 300 enzymes, participates in the synthesis of proteins, carbohydrates and fats, regulates cell sap pH and promotes phosphorus uptake. With magnesium deficiency, plants exhibit chlorosis (yellowing) of lower leaves, premature leaf fall, weakened growth and reduced yields. Magnesium fertilizers allow these disorders to be eliminated and increase photosynthetic efficiency.

Main methods of applying magnesium fertilizers:

• Basic soil application. Magnesium sulfate or kieserite is applied in spring during soil preparation together with nitrogen and phosphorus fertilizers, or in autumn before digging. Application rates of kieserite for most crops are 200–300 kg/ha, for cereals and grain legumes — 40–70 kg/ha.

• Foliar feeding. Spraying plants with magnesium sulfate solutions (typically 1–2% concentration) during the growing season, especially in phases of intensive growth and fruit formation. This allows magnesium deficiency to be quickly corrected.

• Application with irrigation water. In fertigation and hydroponic systems, soluble forms of magnesium sulfate are used.

The most responsive crops to magnesium are tomatoes, cucumbers, peppers (especially in protected ground), fruit trees (apple, pear, cherry), berry crops, potatoes, sugar beet, as well as flower and ornamental crops and lawn grasses. Magnesium fertilizers are especially effective on light-textured soils and in areas with signs of magnesium starvation.

Safety and Storage

Magnesium sulfate belongs to low-hazard substances. When working with it, personal protective equipment (respirator, safety goggles, gloves) is recommended to prevent irritation of mucous membranes by dust. Storage is carried out in dry, well-ventilated areas, in hermetically sealed containers, away from food products and feed. The shelf life of magnesium fertilizers under proper storage conditions is several years.

Conclusion

Magnesium fertilizers remain an important element of the plant nutrition system, especially on soils with low available magnesium content. A wide range of forms — from rapidly soluble epsomite to prolonged kieserite and complex compositions — allows the optimal product to be selected for any crop and cultivation technology. Organising supplies of magnesium fertilizers, including the selection of form and concentration, requires an individual approach.