Rashi on Genesis 41:48/רש"י על בראשית מ״א:מ״ח

1אכל שדה העיר אשר סביבתיה נתן בתוכה THE FOOD OF THE FIELD WHICH WAS ROUND ABOUT EVERY CITY LAID HE UP IN THE SAME — for every district preserves its own produce; and for this people always put amongst the grain some of the earth of the place in which it grows and this prevents it decaying (Genesis Rabbah 90:5).