The affix ḍāc comes after the word 1. dvitīya 2. tṛtīya 3. śamba and 4. bīja when connected with the verb kṛ 'to make' and meaning 'to plough in such a way'.,
The repetition of the word कृ in this sutra indicates that the भू and अस्ति are not to be taken. Thus द्वितीया करोति = द्वितीयं कर्षे (= विलेखनं) करोति 'he makes the second ploughing of the field'. So also तृतीया करोति, शम्बा करोति 'he makes the field ploughed contrariwise to what it was ploughed before = अनुलोम कृषं क्षेत्रं पुनः प्रतिलोमं कृषति ॥ So also बाजी करोति = सहबीजेन विलेखनं करोति ॥
Why do we say when meaning \to plough\ ? Observe द्वितीयं करोति पदम् ॥,