Yerushalmi Kilayim 3:5 ירושלמי כלאים ג׳:ה׳

MISHNAH: If one’s field was sown with onions and he desired to plant there rows of pumpkin, Rebbi Ismael says, he uproots two rows, plants one row, and leaves two rows of onion standing, uproots two rows, plants one row⁹¹A row of vegetables together with its surroundings is four cubits wide. In the interpretation of Maimonides, R. Ismael requires that a swath eight cubits wide be cleared, in which a row of pumpkin four cubits wide is planted. Hence, in the interpretation given in the Halakhah, he envisages a field with a regular pattern: Eight cubits wide onions, two cubits fallow, four cubits pumpkins, two cubits fallow, eight cubits onions, etc. (R. Simson takes the Mishnah to mean that eight cubits have to be fallow between any two beds of onion.)
Since onions usually are planted, not sown, either the language of the Mishnah is imprecise or one speaks of a field in which onions were sown and then thinned to produce straight rows.. Rebbi Aqiba says, he uproots two rows, plants two rows, and leaves two rows of onion standing, uproots two rows, plants two rows⁹²R. Aqiba requires only one furrow between different kinds. He has parallel strips of equal width, alternatingly pumpkins and onions. Then the farmer has to watch closely lest the pumpkins expand into the domain of the onions. (R. Simson holds also in this case that eight cubits have to be fallow between any two beds of onions; R. Aqiba holds that four of these eight are for tending the onions, four for tending pumpkins, and that for a single row of pumpkins one does not have to provide space around them. He holds that for a single row of pumpkins, R. Aqiba requires only four cubits to be fallow between any two beds of onions.). But the Sages say, if between one row and the next is less than twelve [cubits], he should not keep the seeds in between⁹³In the interpretation of Maimonides, the Sages require only that between any two strips of pumpkin there be 12 cubits distance, but they do not require any fallow land between pumpkins and onions, except for the obligatory single furrow. In the interpretation of R. Simson, the total fallow land between two such rows must be 12 cubits, or six cubits between any two strips of differing kinds..

HALAKHAH: (He who plants his vineyard, etc.)⁹⁴This should be a quote from the Mishnah but is from Mishnah 4:9 and should be disregarded.. Cahana said, according to the words of Rebbi Ismael sometimes there are 16, sometimes 12, sometimes 8⁹⁵According to Rav Cahana, all R. Ismael requires is an empty swath four cubits wide, but its placement is arbitrary. Hence, if the pattern is 4 cubits pumpkin, 4 cubits empty, 8 cubits onions, 4 cubits empty, 4 cubits pumpkin, the distance from the last row of the first set of pumpkins to the first row of the second set of pumpkins is 4+8+4 = 16 cubits. If the pattern is regular, as explained in the Mishnah, the distance is 2+8+2 = 12. If the empty spaces are all at the far side of the pumpkins, away from the onions, then the space is only 8 cubits (+ the space of the required furrows, half of which can be accounted for by the rows of pumpkins, leaving one hand-breadth empty from the space of the onions.). When he gives all the working space in the interior, 16. Part interior and part exterior, 12. All exterior, 8. Samuel says, it always must be 12⁹⁶This is the pattern explained in Note 92, regular empty spaces two cubits wide between any two different species. This interpretation is accepted because it is supported by the following baraita.. We have stated thus: “It is determined according to the statements of both of them: Rebbi Ismael says 12, Rebbi Aqiba says 8.” Now, Rebbi Ismael says 12, and the rabbis say 12; in what do they disagree? Closing up! In the opinion of Rebbi Ismael one may not close up, but the rabbis say he may⁹⁷R. Ismael requires empty strips two cubits wide but the rabbis would accept an onion patch 12 cubits wide, separated from the pumpkins only by an empty furrow..