《北史·本记·卷三》
一个成年男子耕种田四十亩，未成年男子耕种二十亩，不要让人有余力，地有遗利。 
一夫制田四十亩，中男二十亩，无令人有余力，地有遗利。 
"A man can farm 40 mu of land. A young man can farm 20 mu of land. Don't let people have surplus energy or land have unused benefits."