Will an application of gypsum improve a clay soil?

FAQ
Question: 

Will an application of gypsum improve a clay soil?

Answer: 

Advertisements for gypsum sometimes claim that gypsum will help loosen heavy, clay soils and improve soil drainage. However, the addition of gypsum to Iowa soils is of little benefit. Gypsum is chiefly used to amend sodic soils. Sodic soils are found mainly in arid regions of the western United States.

Core aerification is the best way to improve growing conditions for lawns established on clay soils. The core aerifier should remove soil cores that are approximately three-fourths of an inch in diameter and 3 inches long. There should be 20 to 40 holes per square foot. April and September are the best times to aerify lawns in Iowa.

Vegetable and flower gardens can be improved by applying and incorporating organic matter, such as compost, well-rotted manure, or peat, into the soil. Work the organic matter into the top 8 to 12 inches of soil.