Mishnayos Sheviis Perek 1 Mishnah 1

עד מתי חורשין בשדה האילן – further on (i.e., in Mishnah 2), it explains what is a שדה אילן /a field containing at least three trees within a distance of a Se’ah (i.e., a cultivated field in which trees grow; an orchard).

ערב שביעית – that it is necessary to add from the sixth year on to the seventh year in the prohibition of working the land, and further on (i.e., Mishnah 4), we will derive it from Biblical verses.

כל שמן שהוא יפה לפרי – that is to say that the ploughing is auspicious for the produce, as he would prepare the ground for the needs of the sixth year and not for the needs of the seventh [year].

עד העצרת – for until Atzeret/Shavuot, it is auspicious for the produce and not for more than that. And from Atzeret and onward, it appears that he is preparing for the needs of the seventh year. But in a bright, shade-less field (vegetable or grain field) where there is no tree, until Passover. But this Mishnah is the “earliest collection of Mishnah/משנה ראשונה and is not the Halakha, for Rabban Gamaliel and his Jewish court counted on these two periods of time, which are Passover for a bright shade-less field and Atzeret/Shavuot for a cultivated field in which trees grow, and permitted them [to work the fields beyond these established times] [so that] it is permitted to plough until Rosh Hashanah of the seventh year.