Which of the following sources is known as an expensive source of magnesium?

Magnesium Sulphate is recognized as an expensive source of magnesium primarily due to its higher production and transportation costs compared to other magnesium sources. This compound typically comes in forms such as Epsom salt, which has a specific set of agricultural applications, and its price reflects these factors.

In contrast, Dolomitic Lime, which is a mixture of calcium and magnesium carbonate, is generally more economical for farms, especially when aiming to amend soil pH while providing magnesium. Magnesium Oxide, while a solid magnesium source, tends to be more concentrated and retains a relatively lower cost when compared to Magnesium Sulphate. Calcium Carbonate, widely used for its liming properties, is also less expensive since it primarily focuses on managing soil acidity rather than acting as a source of magnesium alone.

Understanding these cost dynamics is crucial for effective nutrient management, as it allows farmers to choose appropriate amendments that not only fit their budget but also meet their soil and crop nutrient needs efficiently.