Commentary for Kilayim 5:3
חָרִיץ שֶׁהוּא עוֹבֵר בַּכֶּרֶם, עָמֹק עֲשָׂרָה וְרָחָב אַרְבָּעָה, רַבִּי אֱלִיעֶזֶר בֶּן יַעֲקֹב אוֹמֵר, אִם הָיָה מְפֻלָּשׁ מֵרֹאשׁ הַכֶּרֶם וְעַד סוֹפוֹ, הֲרֵי זֶה נִרְאֶה כְּבֵין שְׁנֵי כְרָמִים, וְזוֹרְעִים בְּתוֹכוֹ. וְאִם לָאו, הֲרֵי הוּא כְגָת. וְהַגַּת שֶׁבְּכֶרֶם עֲמֻקָּה עֲשָׂרָה וּרְחָבָה אַרְבָּעָה, רַבִּי אֱלִיעֶזֶר אוֹמֵר, זוֹרְעִים בְּתוֹכָהּ, וַחֲכָמִים אוֹסְרִים. שׁוֹמֵרָה שֶׁבַּכֶּרֶם, גְּבוֹהָה עֲשָׂרָה וּרְחָבָה אַרְבָּעָה, זוֹרְעִין בְּתוֹכָהּ. וְאִם הָיָה שֵׂעָר כּוֹתֵשׁ, אָסוּר:
A trench that passes through a vineyard ten [handbreadths] deep and four [handbreadths] wide, Rabbi Eliezer ben Yaakov says, If it [the trench] is open [runs through] from the beginning of the vineyard to the end, it has the appearance of being two vineyards and one may sow in it, and if not, it is [viewed] as a winepress [in a vineyard where it is forbidden to sow]. A winepress in a vineyard, ten [handbreadths] deep and four [handbreadths] wide, Rabbi Eliezer says, one may sow in it, and the Sages say forbid it. A watch-mound [where the watchman stands] in a vineyard ten [handbreadths] high and four [handbreadths] wide, one may sow in it, but if the ends of the vine-branches became entwined [over the mound] it is forbidden.
English Explanation of Mishnah Kilayim
English Explanation of Mishnah Kilayim
According to Rabbi Eliezer if the trench is ten handbreadths deep and four wide it is considered to be its own domain and not part of the vineyard. The depth causes the sides to be treated as if they were walls, and the width gives the trench significance. Furthermore, the trench must go all the way through the property from one end to the other, causing the two sides of the vineyard to look as if they were owned by different people. If the trench does not go all the way through the property, then he regards it in the same way that the sages in the next section regard a winepress and it will be forbidden to sow seeds there.
English Explanation of Mishnah Kilayim
Rabbi Eliezer permits one to sow seeds in a winepress (assumedly one no longer used) as long as it is ten handbreadths deep and four wide. Evidently, Rabbi Eliezer is more lenient than the other rabbis and doesn't require the winepress to pass through the entire length of the property. The other sages, however, disagree and hold like Rabbi Eliezer ben Jacob that this is prohibited unless the trench/winepress runs from one end of the vineyard to the other.
English Explanation of Mishnah Kilayim
A watchman's mound is an elevated space upon which they would build a hut for the watchman to sit in while guarding the vineyard. If this mound is ten handbreadths high and four wide then they may sow seeds on it. However, if the ends of vines are entangled in the air over the mound then the mound is considered to be part of the vineyard and one cannot sow there. It seems that the trench, however, would be permitted even if the vines are entangled in the air over the trench. The reason would be that these vines do not come into the ten handbreadths of the depth of the trench, whereas they do come in the ten handbreadths of the height of the mound.