Reference for Kilayim 4:8
הַנּוֹטֵעַ שְׁתֵּי שׁוּרוֹת, אִם אֵין בֵּינֵיהֶן שְׁמֹנֶה אַמּוֹת, לֹא יָבִיא זֶרַע לְשָׁם. הָיוּ שָׁלֹשׁ, אִם אֵין בֵּין שׁוּרָה לַחֲבֶרְתָּהּ שֵׁשׁ עֶשְׂרֵה אַמָּה, לֹא יָבִיא זֶרַע לְשָׁם. רַבִּי אֱלִיעֶזֶר בֶּן יַעֲקֹב אוֹמֵר מִשּׁוּם חֲנִינָא בֶן חֲכִינַאי, אֲפִלּוּ חָרְבָה הָאֶמְצָעִית וְאֵין בֵּין שׁוּרָה לַחֲבֶרְתָּהּ שֵׁשׁ עֶשְׂרֵה אַמָּה, לֹא יָבִיא זֶרַע לְשָׁם, שֶׁאִלּוּ מִתְּחִלָּה נְטָעָן הֲרֵי זֶה מֻתָּר בִּשְׁמֹנֶה אַמּוֹת:
If one plants two rows of vines, if there is not eight cubits between them [the vines] he may not bring [sow] seeds there. If there were three [rows of vines], if there is not sixteen cubits between one row and the other, he may not bring [sow] seeds there. Rabbi Eliezer ben Yaakov says in the name of Chanina ben Chachinai, Even if the middle one [row] was laid waste, and there are not sixteen cubits between one row and the other, he may not bring [sow] seeds there, for had he, originally planted [just] these [two rows] it would have been permitted [to sow between them] if there were eight cubits [between them].