1. Would a person who makes a neder against having benefit from a friends field still be assur to have benefit from the field if the field is sold or made hefker. And is there a difference between metaltelin and karka regarding transfer or is it only by hefker.
2. What is the basis to say that karka that becomes hefker doesn't need to be maisered, isn't the crop automatically tevel at the moment the obligatiion to maaser kicks in, and if the braisa is talking about hefker before the moment maaser obligation takes over, why doesn't it say so. And isn't maaser a function of the shmitah cycle not effected by how long you own it?
Mark Berman, Englewood, NJ
1. The Mishnah on 46a (5:3), with reference to the very case of which you are speaking, permits the Mudar to have benefit from the field if the owner sold it or died (the Tana does not mention Hefker), provided the Lashon ha'Neder was not to have benefit from Ploni's field, but if he said 'from this field', then it remains forbidden.
The Tana talks about selling the field and the Poskim (YD 216:4) equate giving it as a Matanah with selling, and they point out that it remains forbidden should the owner sell it to the Noder himself. They do not mention Hefker either, and I assume that it is the same as selling or Matanah.
And this is borne out by the Mishnah on 43a (4:8), which discusses a similar case, where the two people are traveling together alone, and the Mudar Hana'ah has nothing to eat, and which permits the Madir to place food on a rock and declare it Hefker. Rebbi Yosi forbids it, but the Halachah is not like him.
2. The Mishnah in Ma'asros (1:1) exempts whatever is not guarded from Ma'asros. The Bartenura cites the Pasuk in Re'eh (14:22) "Aser Te'aser Es Kol Tevu'as Zarecha", from which the Yerushalmi Darshens "Zarecha", 'ha'Meyuchad Lach, Prat le'Hefker she'Ein Lo Ba'alim'.
The Tiferes Yisrael comments that this applies even if someone subsequently acquires the field from Hefker and performs Miru'ach (flattening the pile of corn after winnowing, which renders the crops subject to Ma'aseros), and certainly if the Miru'ach was performed while it was still Hefker. In fact, the only time Hefker is Chayav Ma'aseros, he concludes, is if the owner declares it Hefker after the Miru'ach.
Interestingly, the Tosfos Yom Tov cites the Bartenura in Pe'ah (1:6), who cites a different Pasuk (also in Re'eh [14:29], in connection with Ma'aser) as the source for the above ruling; namely, "u'Va ha'Levi Ki Ein Lo Chelek ve'Nachalah Imach", from which the Yerushalmi Darshens that Ma'aseros are confined to property in which the tribe of Levi has no portion, to preclude Hefker, in which they have as much right as a Yisrael. The Bartenura there also cites most of the rulings cited in Ma'aseros by the Tiferes Yisrael.
Be'Virchas Kol Tuv