Parashas Naso · Passuk 5:09
So, too, any gift among the sacred donations that the Israelites offer shall be the priest’s.
Chabad.org — English translation + Rashi
Source: Bava Kamma 110b.
English: “And every heave-offering” — it was taught: R’ Akiva says: Scripture comes to teach that if a person wishes to make his entire threshing-floor terumah, he is permitted.
In context: The expansive language allows designating more than the minimal measure as terumah.
Custom
Chazal permit a person to declare his entire crop as terumah if he so chooses.