פירוש על דברים 11:17

את יבולה [THE GROUND WILL NOT GIVE] ITS יבול — it will not yield even as much as what you have brought (יבול) to it (even the same quantity of seed you have sown in it), just as it is said, (Hag. 1:6) “You sow much, but bring in little” (Sifrei Devarim 43:28; cf. Rashi on Leviticus 26:20).

and as a result of such a development ואבדם מהרה, from hunger, which is a more painful death than dying by the sword.. Therefore, remain on guard!

לא תתן את יבולה, "it will not yield its produce." Although Moses had already said that G'd would lock the heavens he repeated that the earth would not yield its produce to tell the people that even if they were to plant their fields adjacent to rivers and wells the earth would not produce a harvest.