Sforno on Leviticus 25:3/ספורנו על ויקרא כ״ה:ג׳

1שש שנים תזרע שדך, the new revelation in this verse is that the land of Israel is so fertile that the same piece of land can remain under cultivation for six consecutive years, although in other countries the land generally is allowed to lie fallow every other year. (compare Baba Batra 36 on this subject.)

2ואספת את תבואתה, as opposed to the soil in the countries adjacent to the land of Israel.