Kilayim, Chapter 3, Mishnah 3. This mishnah continues to discuss the permitted ways of planting two different species alongside one another. It opens with a law we have already encountered: a rosh tor of vegetables - the triangular corner of a field - that extends into a field of another kind of vegetable is permitted. The reason: since it comes at the corner, at the point of the triangle, it "nir'eh k'sof sadehu" - it looks like the end of his field, and it does not appear as a mixture of two species.
Planting a row of another species inside a planted field:
The mishnah now deals with the following case: his field is planted with one kind of vegetable, and he wishes to plant an entire row of a different kind of vegetable in the middle of that field. All agree that a separation is required between the new row and the rest of the vegetables in the field, and it is made by means of a furrow - a groove of plowed field running along both sides of the new row - but the Tanna'im disagree about its measurements:
Rabbi Yishmael: the furrow must run all the way through, from one end of the field to the other. That is, the separation running along both sides of the new row must continue the entire length of the field - a complete separation.
Rabbi Akiva: he disagrees and holds that a furrow six tefachim long and six tefachim wide is enough. When there is a separation of six by six, the species may come close above it, beyond it and beneath it, and there is no need for the separation to be maintained at that same distance along the entire length.
Rabbi Yehudah: he agrees with Rabbi Akiva about the length - six tefachim - and disagrees with him about the width: a width of "kimlo rochav ha'parsah" - the full width of a hoofprint, the width of a footprint, which is one tefach, is enough. It emerges that a furrow six tefachim long and one tefach wide suffices to separate the new row of vegetables from the field planted with another species.
A further explanation of the dispute:
Among the commentators there is another view in understanding the dispute in our mishnah: the measurements stated by the Tanna'im do not describe the furrow separating the new row from the existing field, but rather the new row itself:
Rabbi Yishmael: the new row must run from one end of the field to the other.
Rabbi Akiva: it is enough for it to be six tefachim long and six tefachim wide.
Rabbi Yehudah: even a length of six tefachim and a width of one tefach suffices.
In summary: in this mishnah we learned that a rosh tor of vegetables extending into a field of another species is permitted, because it looks like the end of his field. We also learned the dispute of the Tanna'im regarding one who plants a row of another species inside a planted field: Rabbi Yishmael requires a furrow running all the way through from the beginning of the field to its end, Rabbi Akiva is satisfied with six tefachim by six tefachim, and Rabbi Yehudah is satisfied with a length of six tefachim and a width of the full width of a hoofprint - one tefach. And we saw a further explanation, according to which these measurements were stated not about the separating furrow but about the new row itself.