How is zakat imposed on farmers, and is it annual or on every harvest?

The passing of a year (hawl) is not a condition for the zakat on crops and fruits, based on the Almighty's saying: (And give its due on the day of its harvest). Zakat becomes obligatory when the produce reaches the nisab, which is five wasqs, based on the Prophet's (peace be upon him) saying: "There is no sadaqa (zakat) on less than five wasqs of dates or grain." The obligatory amount is one-tenth for what is irrigated without cost (by rainwater or rivers), and one-half of one-tenth for what is irrigated with cost (by irrigation animals or similar means), based on the Prophet's (peace be upon him) saying: "For what is watered by the sky and springs, or what is naturally irrigated (athariya), there is one-tenth, and for what is irrigated by means of irrigation animals (nadh), there is one-half of one-tenth."