Adam Clarke on Psalms 72:16

There shall be a handful of corn - The earth shall be exceedingly fruitful. Even a handful of corn sown on the top of a mountain shall grow up strong and vigorous; and it shall be, in reference to crops in other times as the cedars of Lebanon are to common trees or shrubs: and as the earth will bring forth in handfuls, so the people shall be multiplied who are to consume this great produce.

And they of the city shall flourish like grass of the earth - There have been many puzzling criticisms concerning this verse. What I have given I believe to be the sense.