This poem was written in time of King Cheng, the second King of Zhou(1115-1079B.C.), showing the kind of mass farming employing 10,000 hands then in existence, supervised by the King himself.
Zhou Song: Festal Hymns and Songs of The Early Zhou.
lis: The ancient li consisted of 300 mu, the mu being a unit of 100 paces square. Here "thirty lis" refers to private land.