Kilayim, Chapter Two, Mishnah Six
This mishnah deals with a person who wants to plant his field in long rows, each row containing a different species. The mishnah describes how he might do this while avoiding the problem of kilayim.
One who wants to lay out his field in long straight rows each sown with a different species:
1) Bet Shammai says: three furrows of newly broken land.
2) But Bet Hillel says: the width of a Sharon yoke.
3) And the words of these are close to the words of these.
Section one: According to Bet Shammai he has to separate these rows with a gap the size of three furrows which are dug on newly planted land. When he separates the rows by this amount each row is considered to be its own field, since they are recognizably distinct.
Alternatively, others interpret Bet Shammai to mean that each row must be of this width. When the rows are of this size, each is considered a separate field and hence, with even a small separation between the different rows, it will be recognizable that each row is a separate field.
Section two: According to Bet Hillel, the rows must be separated by the width of the size of the yoke used in Sharon, the lowlands inside the coast of Israel.
According to the other understanding, the rows must be of this width.
Section three: The anonymous mishnah notes that there is not that great of a difference between the sizes of the furrows separating the rows (or the size of the rows) mentioned by Bet Shammai and Bet Hillel.