Albert Barnes Commentary 1 Kings 4:7

"And Solomon had twelve officers over all Israel, who provided victuals for the king and his household: each man had to make provision for a month in the year." — 1 Kings 4:7 (ASV)

Requiring a portion of produce from subjects, in addition to monetary payments, is a common practice for Eastern monarchs. This was the practice in ancient Persia, and it continues in modern times.