Tosefta על סנהדרין 175:9

A Kohen or a Levite who sold the produce of their field to a Yisrael, [as to anything] connected to the ground, the tithes are theirs, [and as to anything] not connected to the ground, until he smooths [the pile] (see Sanhedrin 88a:13) -- the tithes are his. He separates Terumah and tithes and gives it to the Kohen, and the remainder is his.