1) WHERE THE BARLEY FOR THE OMER MUST GROW
QUESTION: The Gemara says that the Jewish people brought the Korban ha'Omer when they entered Eretz Yisrael. The Gemara questions how they were able to grow grain for the Korban in such a short amount of time. From the time they entered the land until the time of the Korban ha'Omer was a period of just five days. They could not have bought the barley from the inhabitants of the land, because the Korban ha'Omer must be brought from barley that ripened in the possession of Jews. The Gemara proves from here that barley is able to ripen within a very short amount of time, the amount of time that passed from when the Jews entered Eretz Yisrael and became field-owners until the time they harvested the barley for the Omer five days later.
Why does the Gemara assume that they had to use barley that grew in their possession while they were in Eretz Yisrael? Perhaps they simply took barley that they had planted before they entered Eretz Yisrael, which grew in their possession in Ever ha'Yarden (Transjordan), where they resided for over a year (and where the families of Reuven, Gad, and Menasheh continued to reside even after the nation entered Eretz Yisrael). Why does the Gemara not suggest that they used the barley which grew in Ever ha'Yarden for the Korban ha'Omer?
(a) The RAN in Nedarim (20b) writes that the Korban ha'Omer may not be brought from grain that grew in Ever ha'Yarden. It must grow in Eretz Yisrael proper.
(b) However, RASHI in Sanhedrin (11b) writes that the Korban ha'Omer may be brought from grain of Ever ha'Yarden. Why, then, does the Gemara here not suggest that they brought that barley?
The answer is that grain from Ever ha'Yarden may be brought for the Korban ha'Omer only when it grew after the Jews entered and settled Eretz Yisrael itself. Before the Jews crossed the Jordan, there was no prohibition against eating Chadash and no obligation to bring the Korban ha'Omer. Since the Omer may be brought only from barley that was prohibited to eat before the bringing of the Korban, the barley from Ever ha'Yarden which grew before they entered Eretz Yisrael did not qualify. (See SIDREI TAHAROS, Kelim 1:5.)
2) SEPARATING MA'ASER WITH THE METHOD OF "TZOVER GERANO L'TOCHO"
QUESTION: The Gemara says that with regard to the Mitzvah to separate Ma'aseros from Kitniyos and the laws of Shevi'is, the produce follows the year in which it took root, or "Hashrashah." Since seeds of Kitniyos which are planted together ripen and are picked at various different times (they do not grow uniformly), the year to which they belong is determined by the time of Hashrashah. All of the plants usually take root at about the same time, and thus there is no need to keep a record of what was picked before Rosh Hashanah and what was picked after Rosh Hashanah.
The Gemara asks that instead of following the time of Hashrashah, all of the produce should be mixed together in one place ("Tzover Gerano l'Tocho"), and then Ma'aser should be separated from that mixture, since "Bilah" works (an equal proportion of Ma'aser will be taken for the produce of each year). The Gemara proves that this method works from the statement of Rebbi Shimon Shezuri, who says that if some Pul ha'Mitzri took root before Rosh Hashanah and some took root afterwards, one may mix them together and separate Ma'aser from the mixture. The Gemara answers that the Halachah does not follow Rebbi Shimon Shezuri.
This answer explains why the Rabanan established that the year in which Kitniyos grew is determined by Hashrashah and not by Lekitah (when the grains are harvested). According to the Rabanan, there is no option of "Tzover Gerano." Why, though, does Rebbi Shimon Shezuri himself maintain that the year of Kitniyos follows Hashrashah? He maintains that "Bilah" works, and thus the year of Kitniyos should follow Lekitah, and one should be able to separate Ma'aser with the method of "Tzover Gerano l'Tocho." (TOSFOS)
(a) The RA'AVAD (in KASUV SHAM) and the TOSFOS YESHANIM in the name of the RI explain that even if it is possible to mix all of the produce together and rely on "Bilah," that is not the ideal way to separate Ma'aser. It is far preferable to follow the time of Hashrashah because perhaps the grains will not mix perfectly (and the grains separated as Ma'aser will not contain the proper proportions of new and old produce).
Why, then, does the Gemara question the opinion of the Rabanan in the first place and ask that it should suffice to put all of the produce in one place and take Ma'aser from there? If the Gemara knows that this method is not the preferable way to separate Ma'aser, what is the Gemara's question? The Rabanan's ruling that Kitniyos should follow the time of their Hashrashah certainly is justified!
The Ra'avad explains that the Gemara is not questioning the logic of the Rabanan who determined that Kitniyos follow the year of their Hashrashah. Rather, the Gemara infers from the Mishnah (which says that Kitniyos from before Rosh Hashanah follow the previous year) that if Kitniyos from one year became mixed with those that grew in another year, there is no way to separate Ma'aseros from the mixture. The Gemara asks that one should be able to mix the grains together and separate Ma'aseros from the mixture, as Rebbi Shimon Shezuri maintains. The Gemara answers that the Mishnah does not agree with Rebbi Shimon Shezuri.
(b) The BA'AL HA'ME'OR writes that Rebbi Shimon Shezuri indeed maintains that the year for Kitniyos is determined by their Lekitah, when they were harvested (as Shmuel rules), and not by Hashrashah. In the Beraisa, he challenges the opinion of the Rabanan who say that the year is determined by the time of Hashrashah. He asks why the Rabanan maintain that the year for Kitniyos follows Hashrashah and not Lekitah. Whether the year is determined by Hashrashah or by Lekitah, it should suffice to mix all of the produce together in one place and separate Ma'aser from the mixture (and thus there is no reason for the Rabanan to rule that the year is determined by Hashrashah).
According to the Ba'al ha'Me'or's explanation, Shmuel's ruling is easier to understand. Shmuel, who rules that the year for Kitniyos is determined by Gemar Pri, says that "the Halachah is like Rebbi Shimon Shezuri." According to the initial way of understanding -- that Rebbi Shimon maintains that Pul ha'Mitzri follows Hashrashah and not Lekitah -- Shmuel's statement is misleading (see RASHI DH Ishtamitsei, who seems to have been bothered by this). According to the Ba'al ha'Me'or's explanation that Rebbi Shimon Shezuri indeed rules that Pul ha'Mitzri follows Lekitah (which is the same as Gemar Pri according to TOSFOS DH Achar), Shmuel's statement is easier to understand.
(c) The RIVA, cited by the TOSFOS YESHANIM, explains that Rebbi Shimon Shezuri maintains that all Kitniyos follow Lekitah and not Hashrashah, since one may rely on "Bilah" and mix them together to separate their Ma'aseros. Only with regard to Pul ha'Mitzri does he rule that the year follows Hashrashah, and for an entirely different reason. The Gemara later (14a) explains that if one does not water plants of Pul ha'Mitzri for thirty days before Rosh Hashanah, the plants are treated like a tree and not like a vegetable. Consequently, they are considered part of last year's produce even if they are harvested after Rosh Hashanah. That type of Pul ha'Mitzri -- which was not watered for thirty days before Rosh Hashanah -- is the type to which Rebbi Shimon Shezuri refers when he says that it follows Hashrashah, the time it took root.