Agronomy Degree Practice Exam

Which source would you choose to add calcium to soil without affecting pH?

1. Agricultural lime

2. Hydrated lime

3. Gypsum

4. Calcite

The correct answer is: Gypsum

Choosing gypsum as a source to add calcium to soil without affecting pH is based on its unique properties. Gypsum, or calcium sulfate dihydrate, provides calcium while not significantly altering the soil's pH levels. This characteristic makes it particularly useful in agricultural practices where soil acidity or alkalinity needs to be maintained for optimal crop growth. In contrast, agricultural lime and hydrated lime are primarily calcium carbonate and calcium oxide, respectively. These compounds are used to raise soil pH, making them ineffective if the goal is to avoid altering acidity levels. Calcite, which is essentially another form of calcium carbonate, would also act similarly by increasing pH when applied to soil. Thus, gypsum stands out as the ideal option for supplying calcium without the unintended consequence of modifying soil acidity, making it an essential component in soil management, particularly in crops sensitive to pH changes.