Three-field system

Medieval crop rotation system

The three-field system is a regime of crop rotation in which a field is planted with one set of crops one year, a different set in the second year, and left fallow in the third year. A set of crops is rotated from one field to another. The technique was first used in China in the Eastern Zhou period and arose independently in Europe in the medieval period.

From Wikipedia, under CC BY-SA. More on occurri.