Magnesium sulfate [MgSO4]

Magnesium salt (MgSO4), white, odourless and water-soluble, known in hydrated form as Epsom salt.

Characteristics

Magnesium makes up about 20 % of the mass of the anhydrous salt.
Source of magnesium and of sulfur in sulfate form.
Occurs in several hydrates, such as kieserite (monohydrate) and Epsom salt.
Its solutions are nearly neutral and barely change soil pH.

Role in the preparation: It supplies soluble magnesium and sulfur to the preparation or to the soil.

Caution: Classified as harmful if swallowed, in contact with skin or inhaled: wear gloves, store it dry, and avoid excess, which can pollute water.

Sources: Magnesium sulfate - Wikipedia

Documentary information: this is neither a recommendation for use nor a plant-protection or veterinary claim. Check your country's regulations before any use.