(Beraisa): One who weeds around Kil'ayim or covers Kil'ayim is lashed;
R. Akiva says, even one who is Mekayem.
Inference: This shows that the Chiyuv for weeding (on Shabbos) is for seeding. It cannot be for plowing, for one is not liable for plowing Kil'ayim!
Rejection (Rabah): No, the Beraisa is like R. Akiva, who obligates for being Mekayem Kil'ayim.
Question: The Seifa is R. Akiva, so the Reisha is not R. Akiva!
Answer: The entire Beraisa is R. Akiva. He explains that one is lashed for weeding or covering Kil'ayim because this is Mekayem.
(Beraisa) Question: "Sadcha Lo Sizra Kil'ayim" forbids only seeding. What is the source to forbid Mekayem?
Answer: (The previous word is Kil'ayim, so we read) "Kil'ayim Sadcha Lo" (Kil'ayim may not be in your field).
Avodah Zarah 64a (Beraisa): We may not dig with a Nochri in a field in which he grows Kil'ayim, but we may uproot with him, to decrease Tiflah (despised matter).
Assumption: This is like R. Akiva, who is Mechayev lashes for Mekayem Kil'ayim. Even though R. Akiva forbids keeping Kil'ayim, he permits taking wages to uproot it, to decrease Tiflah.
Rejection: No, the Beraisa is Chachamim. He works for free. It is like R. Yehudah, who forbids giving a free gift to Nochrim. For the sake of decreasing Tiflah, he permits uprooting.
Makos 21b (Mishnah): One can be lashed for eight Aveiros for plowing one furrow: it is Kil'ai ha'Kerem, in Shevi'is...
(R. Yanai): Rabanan concluded that one who covers seeds of Kil'ayim is lashed.
R. Yochanan: Our Mishnah teaches this. One set of lashes is for Kil'ayim, i.e. covering seeds of Kil'ayim!
Reish Lakish: R. Yanai agreed with you. If not, I would have said that the Mishnah is like R. Akiva, who is Mechayev lashes for being Mekayem!
Shabbos 139a: Benei Bashkar asked about hops in a vineyard. Rav Menasiyah answered that they are Kil'ayim.
Question: He should have answered like R. Tarfon! (In any argument about agricultural laws,) in Chutz la'Aretz the Halachah follows the lenient opinion for Eretz Yisrael!
(Beraisa - R. Tarfon): Hops in a vineyard are not Kil'ayim;
Chachamim say, they are Kil'ayim.
Answer: Benei Bashkar are not Benei Torah (they are prone to extrapolate and permit more).
Rav announced that one may plant hops in a vineyard.
Rav Amram Chasida lashed people who did so.
Rav Mesharshiya gave a Perutah to a Nochri child to plant them for him.
He did not pay a Yisrael child to do so, lest the child continue to do so when he matures. He did not hire a Nochri adult, lest he be confused with a Yisrael (adult).
Question: How can R. Akiva say that one is lashed for Mekayem? It is Lav she'Ein Bo Ma'aseh!
Answer #1 (Aruch, Erech Kam): R. Akiva holds that one is lashed for a Lav she'Ein Bo Ma'aseh.
Rebuttal and Answer #2 (Tosfos Avodah Zarah 64a DH Rebbi): R. Akiva holds that one is not lashed for Lav she'Ein Bo Ma'aseh (Makos 21b)! Rather, he is lashed if he made a fence around them, like Rashi says.
Answer #3 (Tosfos Bava Kama 81a DH Ein): R. Akiva means that Mekayem is forbidden. One is not really lashed, for it is a Lav she'Ein Bo Ma'aseh. Chachamim also forbid if he is happy that the Kil'ayim is there, even if he did not plant it.
Ri Korkus (Hilchos Kil'ayim 1:3): Tosfos holds that Chachamim forbid to be Mekayem but exempt from lashes even mid'Rabanan. The Rambam holds that Chachamim exempt even if he makes a fence, as long as he does not weed or water them.
Rambam (Hilchos Kil'ayim 1:3): One may not plant Kil'ayim for a Nochri. One may tell a Nochri to plant Kil'ai Zera'im for himself. One may not Mekayem Kil'ai Zera'im in his field; he must uproot it. If he was Mekayem, he is not lashed.
Rebuttal (Ra'avad): We permit in Chutz la'Aretz, but not in Eretz Yisrael! Even one who is Mekayem is lashed! The Yisrael will weed and water them - this is Mekayem! Also, the Gemara never resolved whether or not one may tell a Nochri to transgress a Lav (Bava Metzi'a 90a), so we are stringent!
Question: Why does the Ra'avad say that one is lashed for Mekayem? The Halachah does not follow R. Akiva!
Answer #1 (Ri Korkus): The Ra'avad holds like Rabah, who says that the entire Beraisa is R. Akiva. Alternatively, they argue about when no act is done (like the Aruch says), but all agree that one who does an act is lashed.
Answer #2 (Radvaz): The Ra'avad does not ask from R. Akiva, for the Halachah does not follow him. Rather, he just shows that Mekayem is so stringent that some say that one is lashed for it.
Defense (of Rambam - Kesef Mishneh): The Ra'avad asked from weeding and watering, for otherwise Mekayem is passive and one is not lashed for it. Indeed, the Rambam permits to be Mekayem, but without weeding or watering! Perhaps Rav Mesharshiya holds that in Chutz la'Aretz the Halachah follows the lenient opinion for Eretz Yisrael regarding planting, but one may Mekayem in Chutz la'Aretz even though it is forbidden in Eretz Yisrael. The Rambam permits even in Eretz Yisrael for one who will not Mekayem, e.g. he will give it for a gift to a Nochri. Alternatively, one may Mekayem before Hashrashah, and sell the seeded field to a Nochri for a high price.
(Ri Korkus): We could say that the Rambam explains that Rav Mesharshiya forbids hops in a vineyard like Chachamim, nevertheless he paid a Nochri to plant it. We may be lenient about Kil'ai Zera'im in Eretz Yisrael like Kil'ai ha'Kerem in Chutz la'Aretz. However, this does not answer why the Yisrael may weed and water the Kil'ayim. Rather, we must say that the Rambam permits telling a Nochri to plant Kil'ayim for the Yisrael in the Nochri's field.
Radvaz: The Rambam discusses telling a Nochri to plant in the Nochri's field. The Yisrael may even say that he will buy the produce, just like one may tell a Nochri 'plow your field in Shemitah, and I will buy it after Shemitah'. Amirah l'Nochri is a problem only if it pertains to property of the Yisrael.
Question (Kesef Mishneh): The Rambam rules that weeding is a Toldah of plowing, like Rabah. If so, he should explain like Rabah that the entire Beraisa is R. Akiva, and all agree that one is liable for Mekayem!
Answer (Kesef Mishneh): Even if the entire Beraisa is R. Akiva, Chachamim disagree. Alternatively, we are unsure whether or not Chachamim disagree, and we are lenient (not to lash) mi'Safek. The Yerushalmi says that Chachamim disagree.
Mishneh l'Melech: In Avodah Zarah it seems that Chachamim permit to be Mekayem.
Rosh (Hilchos Kil'ayim (after Menachos) 3): It is forbidden to plant or Mekayem Kil'ai ha'Kerem, and they are Asur b'Hana'ah. It is forbidden to plant or Mekayem Kil'ai Zera'im, but one may eat them, and all the more so one may benefit from them. Reuven may not allow a Nochri to graft onto Reuven's tree. He may not even let him plant hops in Reuven's vineyard (Shabbos 139a).
Hagahos Ashri (Avodah Zarah 5:3): Levi may hire himself to a Nochri to uproot Kil'ayim, even though Levi wants the Kil'ayim to endure until he uproots it. Even R. Akiva, who forbids to be Mekayem, permits this, in order to decrease Tiflah.
Tosfos (Shabbos 139a DH Rav): Even though the Halachah follows R. Tarfon in Chutz la'Aretz, Rav Amram and Rav Mesharshiya needed to be stringent, for people in their regions were not Benei Torah.
Or Some'ach (Avodah Zarah 3:10): One cannot say that the Isur to Mekayem (idolatry or anything else) applies only to something Asur b'Hana'ah. The Gemara said that if the Beraisa (that permits uprooting Kil'ayim from a Nochri's field) is like Chachamim, even to be Mekayem is permitted. It must discuss Kil'ai Zera'im. If it was Kil'ai ha'Kerem, the Yisrael benefits from Isurei Hana'ah! Even though one may eat Kil'ai Zera'im, one is lashed for being Mekayem (according to R. Akiva).
Shulchan Aruch (YD 295:7): It is forbidden to be Mekayem a tree grafted Kil'ayim. The fruit is permitted even to the one who grafted. One may plant a branch of the grafted tree elsewhere.
Beis Yosef (DH v'Asur): We equate grafted trees to Kil'ai Zera'im.
Shulchan Aruch (YD 296:13): If seeds were accidentally dropped or blown into a vineyard and they sprouted, nothing is forbidden. The Torah forbids "Asher Tizra"; this was not planted. One is obligated to uproot the growth when he sees it.
Gra (27): He is obligated lest he be Mekayem Kil'ayim.
Tur and Beis Yosef (Reish ha'Siman DH Kil'ai): The Torah forbids to be Mekayem Kil'ai ha'Kerem in Eretz Yisrael (Kil'ayim 8:1).
Shulchan Aruch (28): If vines rest on a trellis and one planted underneath an empty part of the trellis, or under part of a tree that does not produce fruit, and the vine grew over the Zera'im, one may not be Mekayem the Zera'im or bend the vine back. He must uproot the Zera'im.
Shulchan Aruch (297:1): In Eretz Yisrael, one who plants Kil'ai Zera'im or covers it is lashed.
Gra (3): This is like Makos 21b; Chachamim agree that one is lashed for covering. Only Rabah (Moed Katan 2b) establishes the entire Beraisa like R. Akiva.
Shulchan Aruch (297:2): One may not plant Kil'ai (Zera'im) for a Nochri. One may tell a Nochri to plant Kil'ai Zera'im for himself. He may not Mekayem them in his field. He must uproot it. If he was Mekayem, he is not lashed. In Chutz la'Aretz one may mix seeds and plant them.
Question: We hire workers to uproot Kil'ayim on Chol ha'Mo'ed. The Beis Yosef (Sof ha'Siman DH Tanan, based on Tosfos 6a DH d'Mozlei) permits even workers who have what to eat. This is unlike the Rivash (226, brought in Rema OC 544:1) who forbids Mitzvos that are not needs of the body!
Answer (Taz 544:1): The Rivash discusses Mitzvos Aseh, which can be done after the Mo'ed. It is Asur to be Mekayem Kil'ayim; one is lashed for this! Also, Tosfos only said that perhaps the Heter does not depend on lacking food.
Gra (DH v'Hu): The Heter for workers to uproot Kil'ayim is only if they lack what to eat (Moed Katan 6a).