Reference for Kilayim 2:4
זְרוּעָה וְנִמְלַךְ לְנָטְעָהּ, לֹא יֹאמַר אֶטַּע וְאַחַר כָּךְ אוֹפָךְ, אֶלָּא הוֹפֵךְ וְאַחַר כָּךְ נוֹטֵעַ. נְטוּעָה וְנִמְלַךְ לְזָרְעָהּ, לֹא יֹאמַר אֶזְרַע וְאַחַר כָּךְ אֲשָׁרֵשׁ, אֶלָּא מְשָׁרֵשׁ וְאַחַר כָּךְ זוֹרֵעַ. אִם רָצָה, גּוֹמֵם עַד פָּחוֹת מִטֶּפַח, זוֹרֵעַ, וְאַחַר כָּךְ מְשָׁרֵשׁ:
If a man's field was sown [with grain or legumes] and then he decided to plant it [with vines], he is not to say, "I will [first] plant and then I will turn it over," but he must turn it over and afterwards plant. If it was planted [with vines] and then he decided to sow it, he is not to say, "I will [first] sow and then uproot," but he must [first] uproot, and then sow. [But], if he desires, he may cut down [the vines] to less than a handbreadth [of the ground and then] sow, and afterwards uproot.