Tosefta su Shevi'it 7:11

There is a stringency with Terumah and second tithe that there is not with first fruits: That Terumah and second tithe apply to [the lands of] Ammon and Moab, which is not the case with first fruits. There is a stringency with second tithe and first fruits that there is not with Terumah: That second tithe and first fruits require one to come to the "place" (i.e., the Temple, the "place" that God has chosen to have his name dwell (see Deut. 14:23 (second tithe), Deut. 26:2 (first fruits)), and they require a confession, and they are forbidden to a mourner -- but Rabbi Shimon permits them [to a mourner]. And they are liable in [the laws of] bi'ur (i.e., the requirement that one uproot produce growing during the sabbatical year, and declare it ownerless (see Sheviit 7:1, 9:4).]. Rabbi Shimon says, first fruits are exempt from bi'ur (Bikkurim 2:2). Rabbi Yosei says, since second tithe requires confession and first fruits require confession, [you must say that] since second tithe requires removal, so too first fruits must require removal as well. Rabbi Shimon said to him, since with second tithe, in which the requirement of bi'ur applies [both to seventh-year produce] as well as to money [exchanged for such produce], you must say that with respect to first fruits, as to which the money exchanged for them does not require bi'ur, [the first fruits themselves do not require removal during the sabbatical year].

We [may] combine fruits [grown] outside the Land of Israel with [exempt, i.e., tithed] fruits [grown] inside the Land of Israel so that they form the majority over [Demai fruits grown] in the Land of Israel in order to exempt them from tithes. We [may] combine fruits [grown] outside the Land of Israel with second-year fruits (i.e., fruits grown in the second year of the agricultural cycle), in order that they form the majority over third-year fruits to exempt them from the second tithe. We [may] combine from the fruits [grown] outside the Land of Israel with third-year fruits in order that they form the majority over fourth-year fruits to exempt them from the poor man's tithe. [?] We [may] combine fruits [grown] immediately before Shevi'it [the seventh year of the agricultural cycle, when fields must lie fallow] in order that they form the majority over fruits [grown during] Shevi'it, to exempt them from Bi'ur ["removal," see Sheviit 7:1]. We [may] combine fruits [grown] outside the Land of Israel with Shevi'it fruits in order that they form the majority over fruits [grown] immediately after Shevi'it in order to exempt them from tithes.