Magnesium sulphate heptahydrate can be used as tanning, explosives, paper, porcelain, fertilizer, and medical oral laxatives. Mineral water additive. Magnesium sulphate is used in agriculture as a fertilizer because magnesium is one of the main components of chlorophyll. It is commonly used in potted plants or crops that are deficient in magnesium, such as tomatoes, potatoes, roses, and the like. Magnesium sulfate has the advantage of being more soluble than other fertilizers. Magnesium sulfate is also used as a bath salt.