Why does the Torah insert the word "Asher Nata Kerem"?
Sotah, 43a-b: To incorporate in the current Halachah someone who a. grafted 1 or transplanted the branch of a vine; b. purchased, inherited or received a vineyard as a gift; 2 c. planted five vines or any other fruit-trees. 3
Sotah (Ibid.): Though not if he grafted it be'Isur (Kil'ayim) as implied by the word "ve'Lo Chil'lo" - See Torah Temimah, notes 24 & 29).
See Torah Temimah, notes 25.
Sotah (Ibid.): But not four fruit-trees - which are not called a vineyard, or five non-fruiit bearing trees - See Torah Temimah, note 27 who queries why this D'rashah is necessary..
What if a soldier owns a vineyard together with a partner?
Sotah, 43b: He does not return from the battle-front, since it is not his vine-yard. 1
The same ought to apply to a room which measures less than eight by four Amos. See Torah Temimah, note 28.
What are the connotations of "ve'Lo Chil'lo"?
Rashi and Targum Yonasan: It means that he did not redeem the fruit in the fourth year - Kerem R'vai (from a Kohen
Targum Yonasan: In Kedoshim Vayikra, 19:24, Targum Yonasan also states that Revai is redeemed from the Kohanim, unlike Chazal, who say that the owner eats it (or food bought with its redemption money) in Yerushalayim. This requires investigation.
