System of regularly changing the crops grown on a piece of land. The crops are grown in a particular order to utilize and add to the nutrients in the soil and to prevent the build-up of insect and fungal pests. Including a legume crop, such as peas or beans, in the rotation helps build up nitrate in the soil, because the roots contain bacteria capable of fixing nitrogen from the air.
A simple seven-year rotation, for example, might include a three-year ley (grassland) followed by two years of wheat and then two years of barley, before returning the land to temporary grass once more. In this way, the cereal crops can take advantage of the build-up of soil fertility which occurs during the period under grass. In the 18th century a four-field rotation was widely adopted; over four years a field might be planted with autumn-sown cereal, followed by a root crop, then spring cereal, and finally a leguminous crop. Innovative farmers such as Charles ‘Turnip’ Townshend improved cultivation techniques.
18th-century developments Landowners in the 18th century were increasingly motivated by the search for better farming methods to increase productivity and profits. The land market was active; numerous long-established landowners were being forced by debt to sell off portions of their estates, and the buyers were frequently newcomers from business backgrounds for whom ownership of land conferred the right to vote. They regarded the running of their farms as another commercial enterprise and, with other landowners, sought to cut costs, improve methods and output, and maximize profits. From 1750 food prices began to rise steadily with the increase in population and, after the outbreak of war with France in 1793, the disruption to food imports. The prospect of high prices encouraged farmers to attempt to raise yields.
From the late 17th century British farmers had been aware of successful Dutch agricultural techniques, which included the sowing of clover seed with barley (clover being a legume with nitrogen-fixing abilities); after the barley harvest, cattle were fattened on the clover crop, their manure further enhancing the soil. During the 18th century enterprising British landowners replaced the old three-field system with a new four-field rotation of crops. Each field was sown annually with a different crop, a four-year rotation typically being turnips (for winter animal feed), followed by barley, clover, and wheat. The system favoured both stockrearing and cereal-growing.
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