If you are interested in learning more about the Irish tithes, a useful source is Dr William Roulston’s book “Researching farming Ancestors in Ireland.” Chapter 6.1 covers tithes.
Between 1735 and the 1820s pasture was exempt. At that point a composite method of calculating tithes was slowly introduced, and pasture was then included. (Roulston p 106).
In most cases the tithes are in Irish acres which are bigger than statute acres. Occasionally in Ulster they were in Scottish Cunningham acres. (Roulston p 108).