Question: The Gemara in the first Perek of Avodah Zarah (Daf 13a & 13b) forbids being Makdish, Machrim and Ma'arich nowadays (See Tosfos Bechoros, 53b), then adds that 'If one did, the animal must be castrated, and the fruit and vessels, left to rot (See Tosfos there 13b DH 'Yerakeivu')' ...

Question (cont.): And the current Sugya is speaking about nowadays, as the Gemara concludes here; so why do we not say 'Let them rot'?

Answer: We must therefore establish 'Let them rot' by Metalt'lin - which will otherwise be abused, should one leave them to rot where they are, whereas here it is speaking about Karka'os, which will be abused if one just leaves them ...

Proof: And the Gemara will indicate them shortly, when it asks 'But the episode in Pumbedisa involved Karka'os?'

Clarification: To assess it monetarily, in order to give the Tovas Hana'h to the Kohen.

Clarification: In Perek ha'Mekabel (Bava Metzi'a, Daf 106a) the Gemara explains that the blast and mildew also occurred everywhere else ...

Reason: Because if it was confined to the majority of that group of fields, the Mishnah would not have stated that it does not count in the number of years ...

Proof: This is also implied by the Mishnah, which puts it together with Shevi'is, when it is forbidden to plant (See Avodah Berurah).

Question: The Gemara explains why the Tana mentions Neirah (fallow) - because since it rules that 'Hovirah' (where the owner did not even plow the field) is counted, how much more so 'Neirah' (where he lowed it but did not plant) ...

Alternative Answer: It could have answered with the principle 'Lo Zu Af Zu Katani' (to state the smaller Chidush first and then the larger one).

Explanation #1: Rashi explains regarding a man who sold his daughter when she was a Ketanah, that he cannot sell her again once she has gone free with Simanim of Na'arus ...

Explanation #1 (cont.): As the Gemara says in Kidushin (Daf 18a & 18b) 'A man cannot sell his daughter for Shifchus after Chifchus' ...

Source: And the Gemara leans this from "be'Vigdo vah" - 'Having dealt with her faithlessly by selling her as a maidservant, he is not permitted to sell her again'.

Explanation #1 (concl.): Consequently it a cplete departure and a Kal va'Chomer is justified (Until here is the wording of Rashi).

Refutation: This is not correct however - since that is subject to a Machlokes Tana'im there?

Explanation #2: The Ri therefore explains that even the opinion that otherwise holds that 'A man may sell his daughter for Shifchus after Shifchus, concedes that, where she brings Simanim, he may not sell her ...

Explanation #2 (cont.): Based on the Kal va'Chomer.

Question: When someone sells his field too, based on the same Kal va'Chomer, it cannot be sold again (See Avodah Berurah)?

Answer: One can differentiate however, inasmuch as it is not quite the same as the Kal va'Chomer by 'his daughter'

Reason: Because since the Simanim of Na'arus that she now possesses will never leave her again ...

Reason (cont.): Whereas when a person sells his field in the Yovel, the Kal va'Chomer is not as strong, since, once the Yovel passes it will revert to its former status.

Reinstating Explanation #1: One can also explain like Rashi - 'Because a person cannot sell his daughter for Shifchus after Shifchus ...

Reason: And even though the Tana'aim argue over this, we Pasken there like Rebbi Shimon, who rules that it is forbidden to sell her.

Question: And if you ask 'It is obvious that when Shmuel rules the sale is Bateil and the money is returned, he is referring to 'ha'Mocher Sadeihu bi'Shenas ha'Yovel' ...