Three-field system

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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. The three-field system lets farmers plant more crops and therefore increase production. Under this system, the arable land of an estate or village was divided into three large fields: one was planted in the autumn with winter wheat or rye; the second field was planted with crops such as peas, lentils, or beans; and the third was left fallow (unplanted). Cereal crops deplete the ground of nitrogen, but legumes can fix nitrogen and so fertilize the soil. The fallow fields would overgrow with weeds which were used for grazing farm animals. Their excrement fertilized that field's soil to regain its nutrients. Crop assignments were rotated...

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