Kieserite is a naturally
occurring mineral that is chemically known as magnesium sulfate monohydrate
(MgSO4·H2O). It is mined from geologic marine deposits and provides a soluble
source of both Mg and S for plant nutrition.
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| Magnesium deficient grapes |
Production
Kieserite is primarily
obtained from deep underground deposits of minerals in Germany. It is present
in the remnants of ancient oceans that were evaporated and are now buried
beneath the earth’s surface.
These mineral resources contain a variety of
valuable plant nutrients. The ore is brought to the surface where the magnesium
salts are separated from potassium and sodium salts using a unique, dry
electrostatic (ESTA) process.
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| Mining in Germany |
The fine crystalline
kieserite is sold for direct application to soil, or it is granulated to a larger
particle size that is better suited for mechanical fertilizer spreading or for
bulk blending with other fertilizers.
Chemical Properties
Chemical formula: MgSO4·H2O
Mg content: 16% (kieserite
fine); 15% (kieserite granular)
S content: 22% (kieserite
fine); 20% (kieserite granular)
Solubility: 417 g/L (20°C)
Solution pH: 9
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| Granular kieserite |
Agricultural Use
Kieserite provides a highly
concentrated form of two essential plant nutrients—Mg and S. Since kieserite
applications have no major effect on soil pH, it can be supplied to all kinds
of soil, irrespective of soil pH. It is commonly used prior to or during the
growing season to meet the nutrient requirement of crops. Due to its high
solubility it can be used to supply both Mg and S during peak periods of crop demand.
Since kieserite is an earth mineral mined from naturally occurring deposits, it
is permitted as an organic nutrient source by some organic certifying
agencies.
Kieserite itself is not used
as foliar fertilizer or in fertigation systems, but it serves as raw material
for the production of Epsom salt (MgSO4·7 H2O), which is totally soluble and
suitable for both fertigation and foliar application.
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| Fine kieserite particles |
Management Practices
Many soils are low in Mg and
require supplemental nutrients to support crop yield and quality.
Sandy-textured soils and soils with a low pH (such as highly weathered tropical
soils) are frequently characterized by a low Mg supply for plants. Under these conditions,
it is a prerequisite to raise the Mg content in the soil by adequate
fertilization.
Splitting Mg applications
into two or more doses is recommended in areas with high precipitation in order
to avoid leaching losses. Soils in temperate climates with higher clay content
may have higher Mg contents and are often less prone to leaching losses.
Fertilizer Mg application
rates vary depending on factors such as the specific crop requirement, the
quantity removed during harvest, and the ability of soil minerals to release
adequate Mg in a timely manner to support crop yield and quality. Kieserite
application rates are typically in the range of 200 to 300 kg/ha for many
crops. Additional Mg and S demands during peak growth periods demand can be met
by foliar application of materials such as Epsom salt or a variety of soluble
nutrient sources.
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| Magnesium deficient soybeans |
This post originally
appeared as one in a series on specific nutrient sources on the IPNI website.
