DAVAR SHE'YESH LO MATIRIN
Answer #3 (Beraisa - R. Shimon): There is no Shi'ur (that can be Batel in a mixture) for any Davar she'Yesh Lo Matirin (there is a time, place or way in which the Isur is permitted), such as Tevel, Ma'aser Sheni, Hekdesh, and Chadash (new grain before the Omer is offered);
For every Davar she'Ein Lo Matirin, such as Terumah, Terumas Ma'aser, Chalah, Orlah, and Kil'ei ha'Kerem, Chachamim fixed a Shi'ur (how much Heter is needed for Bitul).
Chachamim: Shemitah is never permitted, yet it is never Batel!
(Mishnah): Any amount of Shemitah produce forbids b'Minah (if it became mixed with Heter with the same species, or if sixth year produce grew additionally in Shemitah).
Version #1 (our text, Rosh) R. Shimon: (In that Mishnah) I said only regarding Bi'ur (if a bulb of Shishis grew in Shemitah, the growth is not Batel and the onion must be eradicated);
Regarding eating (if Peros Shemitah were mixed with Heter), if they do not give taste to the mixture, they are Batel (since Ein Lo Matirin).
Version #2 (Ran's text) R. Shimon: That Mishnah applies only to (before) Bi'ur (Shemitah produce is permitted before Bi'ur, so it is Yesh Lo Matirin and it is not Batel);
Regarding eating (a mixture after Bi'ur), if the Shemitah produce does not give taste to the mixture, it is Batel (since Ein Lo Matirin). (end of Version #2)
Rejection: Perhaps here also we are stringent to say that the bulb is not Batel!
IS A BULB BATEL IN ADDITIONAL GROWTH?
Answer #4 (Mishnah): If onions were in the ground in Shemitah and rain fell and they sprouted:
If the leaves are black, they are forbidden. If they are green, they are permitted;
R. Chanina ben Antigonus says, if they can be uprooted by the leaves, they are forbidden;
Regarding Shemitah onions which resumed growing in Sheminis, if the leaves grew this amount [the new growth is the majority], the onions are permitted.
Inference: A forbidden bulb is Batel in permitted growth!
Rejection: Perhaps the Mishnah discusses onions that were mashed (they are unimportant, therefore they are Batel in the added growth).
Answer #5 (Beraisa): One who weeds with a Nochri in Chasayos (this will be explained) may eat from them (before tithing) Arai (haphazardly). One tithes them like Vadai Tevel (before eating Kavu'a);
R. Shimon ben Elazar says, (if he was weeding) in Sheminis he may eat Chasayos of a Yisrael suspected of transgressing Shemitah.
Inference: The added growth in the eighth year nullifies the bulb (of Shemitah)!
Suggestion: This is no proof. Perhaps R. Shimon permits species in which the seed disintegrates!
Rejection (Beraisa): Chasayos are species like lupines, garlic, and onions (in which the seed remains).
Suggestion: This is no proof. Perhaps the case is, the produce was ground up (Ran - before it was planted; Rosh - after it was harvested, and it was mixed with Heter)!
Rejection: The Beraisa discusses one suspected of transgressing Shemitah. He would not bother to grind up the produce!
Suggestion: This is no proof. Perhaps the produce was mixed up with Heter!
Rejection: The Beraisa allows one to eat while weeding, when it is not mixed up!
Suggestion: This Beraisa refutes R. Yochanan and R. Yonasan (57b).
Rejection (R. Yitzchak): Shemitah is different. Since the Isur comes through land, the Isur can be Batel even while attached to the land.
Question: The Isur of Ma'aser comes through land, but it is not Batel while attached!
(Beraisa): If Terumas Ma'aser was not separated from a Litra of Ma'aser Rishon, and it was planted, and it is now 10 Litras, Ma'aser and Shemitah apply to the produce;
Tithes on the initial Litra must be separated from other produce.
Answer: The obligation to tithe does not come from the land, rather from Miru'ach (final processing).