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1. The three-field system is a regime of crop rotation in use in medieval and early-modern Europe from around the time of Charlemagne. Crop rotation is the practice of growing a series of similar types of crops in the same area in sequential seasons, but farmers were not allowed to choose their crop but had to farm what was being grown in that field. 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 other crops such as peas, lentils, or beans; and the third was left fallow, in order to allow the soil of that field to regain its nutrients. With each rotation, the field would be used differently, so that a field would be planted for two out of the three years used, whilst one year it "rested". This allowed farmers to plant more crops and therefore to increase production. With more crops available to sell, this also helped the economy in general to thrive. The introduction of the three-field system and the adoption of the moldboard plow were parallel developments which worked hand in hand to increase the productivity of the land.
2. Three-field system, method of agricultural organization introduced in Europe in the Middle Ages and representing a decisive advance in production techniques. In the old two-field system half the land was sown to crop and half left fallow each season; in the three-field system, however, only a third of the land lay fallow. In the autumn one third was planted to wheat, barley, or rye, and in the spring another third of the land was planted to oats, barley, and legumes to be harvested in late summer. The legumes (peas and beans) strengthened the soil by their nitrogen-fixing ability and at the same time improved the human diet.
Because spring planting required summer rains, it was principally effective north of the Loire and the Alps. By providing two harvests a year it reduced the risk of crop failure and famine. It also made plowing more effective by two means. First, by doing slightly more plowing than under the two-field system, a community of peasants could roughly double their crop yield, though in practice the fallow was usually plowed twice to turn under the green manure. Secondly, the cultivation of a surplus of oats in the spring planting provided feed that made possible the substitution of the swifter gaited horse for ox power, after the introduction of the padded horse collar.
One of the first Germans to question this system, and new ways of expanding beyond this medieval system was Johann Friedrich Mayer, in his 1769 work Lehre vom Gyps als vorzueglich guten Dung zu allen Erd-Gewaechsen auf Aeckern und Wiesen, Hopfen- und Weinbergen.
- Roeber, A. G. (1998). Palatines, Liberty, and Property: German Lutherans in Colonial British America. p. 58.