Why not take a sample down to the local agricultural extension office? (surely that isn't too "primitive" for "the rest of us") There's almost no part of the country without one - if not an agricultural school and/or some sort of agriculture, in general... It takes only one test, one time, to determine what is needed for the way you plant your crops, in your area.
It makes more sense to add it if it's proven to be necessary for your growing conditions, than if done on pure faith, or based on the word of experience of others. (call me untrusting, I don't mind) What works for me won't necessarily work for you. That might be the clause that is lost all too frequently in the discussion. I think it's important to ask WHY. Maybe you don't. Either way...