Sahih Bukhari: Hadith 1435

The Prophet (ﷺ) said, "On a land irrigated by rain water or by natural water channels or if the land is wet due to a near by water channel Ushr (i.e. one-tenth) is compulsory (as Zakat); and on the land irrigated by the well, half of an Ushr (i.e. one-twentieth) is compulsory (as Zakat on the yield of the land)."