Kiddushin, Chapter 1, Mishnah 9. This mishnah addresses the question of which mitzvos apply only in Eretz Yisrael, and which apply outside the Land as well.
The words of the mishnah:
"Kol mitzvah shehi teluyah ba'aretz einah noheget ela ba'aretz" - every mitzvah that depends on the land, meaning that it has to do with agriculture and with things attached to the ground, applies only in Eretz Yisrael. For example: Terumah and tithes, and the like.
"V'she'einah teluyah ba'aretz noheget bein ba'aretz bein b'chutz la'aretz" - mitzvos that are not connected to the land and have no relation to the soil itself apply wherever a person happens to be.
"Chutz min ha'orlah v'hakilayim" - except for orlah and kilayim:
Orlah: the prohibition against eating or deriving benefit from the fruit of a tree during the first three years after it is planted. Although this is a mitzvah that depends on the land, it applies outside Eretz Yisrael as well, and this is by force of a halachah l'Moshe miSinai - a tradition reaching back to Sinai, that by Torah law itself orlah applies even outside the Land.
Kilayim: the prohibition of kilayim also applies outside the Land. But a precise distinction is needed: outside the Land it is only rabbinic, and only with regard to kilei hakerem - planting other species in a vineyard - and not with regard to kilei zera'im, which is a mixture of different kinds of vegetables and seeds. Kilei zera'im does not apply outside the Land at all, not even rabbinically. The reason lies in the stringency of kilei hakerem, which is forbidden even to derive benefit from, unlike kilei zera'im; and because of this stringency the Sages extended the prohibition to outside the Land as well.
The view of Rabbi Eliezer - the prohibition of chadash:
Rabbi Eliezer says: "Af min hachadash" - also from the new grain. The prohibition against eating or harvesting the new grain until the Omer offering has been brought, or until the sixteenth of Nisan has passed, applies outside the Land as well, even though this is a mitzvah that depends on the Land and on something attached to the ground. So Rabbi Eliezer holds, and most of the poskim follow him, since the verse says regarding chadash: "in all your dwelling places."
And since we are dealing with the law of chadash outside the Land, this is a fitting place to note the practical halachah: since we do not have the Omer offering, the new grain remains forbidden throughout the entire day of the sixteenth of Nisan. Outside the Land the prohibition extends in practice through the whole of the seventeenth as well, because of sefeika d'yoma - the doubt that once existed in establishing the new month. Just as we keep two days of Yom Tov, so too we keep the prohibition of chadash until the seventeenth of Nisan.
In summary: in this mishnah we learned the rule that mitzvos which depend on the land apply only in Eretz Yisrael, while those that do not depend on it apply everywhere. Two exceptions were listed: orlah, which applies outside the Land by a halachah l'Moshe miSinai, and kilayim, which applies there rabbinically and only with regard to kilei hakerem, because of the stringency of the prohibition against deriving benefit. And according to Rabbi Eliezer, whose view most of the poskim adopt, the prohibition of chadash also applies outside the Land, by force of the verse "in all your dwelling places."