What is the meaning of "Sefi'ach Ketzircha"?
Rashi and Ramban: 'Sefichim' are crops that grow from seeds that fell during the harvest - that one did not plant 1 - which are included in the Isur.
What are the implications of "Lo Siktzor?
Rashi and Ramban: It implies that one may not harvest it in the way that an owner does, but declare it Hefker. 1
Ramban (citing a Bereaisa): According to R. Akiva however, Sefichim are entirely forbidden (See Ramban, DH 've'Achshav' and 'u'le'Kach' and subsequent Diburim, who elaborates at length).
What are the implications of "Nezirecha?
Rashi and Targum Yonasan: It refers to the grapes from which one separated others and did not declare Hefker.
Ramban #2 (citing Targum Onkelos, It means grapes that one abandoned, leaving them to the worms and thorn-bushes. 3
Ramban: The equivalent of "Sefichim" by the crops.
Ramban: In any event, the fact that the Torah uses the word "Nezirecha" to describe a vineyard that is not worked, is due to its similarity to a Nazir, who who, forbidden to eat grapes and all their by-products, does not work his vineyard, and explains the Minhag to refer to an un-worked vineyard as 'Nazir'.
What are the implications of "Ve'es Invei Nezirecha Lo Sivtzor"?
Rashi and Ramban #1: It implies that one may not harvest the grapes that one separated from others, 1 only from those that are Hefker.
Ramban #2: The Torah is merely issuing the dual prohibition of personally harvesting one's wild crops on the one hand, and one's wild grapes, 2 on the other.