Adding gypsum to make the soil better

I happened to run into a horticulturist recently . I enquired if it would be good for the plants if I added some red soil. he suggested that it was not important to add new soil but to improve the soil which is there in the garden. He suggested that I should add Gypsum to make the soil better.
Does anyone have any opinion on this? I would like to keep my garden an organic garden. Will adding gypsum make it chemical?