crop rotation

crop rotation The practice of growing different crops in different years on the same land, in order to prevent the soil's nutrients from being exhausted and to reduce the risk of a build-up of diseases and pests specific to one crop. Crop rotation was widespread in Europe from the time of the ROMAN EMPIRE. Two-field rotation was practised by the ancient Greeks: one half of a farmer's land was planted in the spring or autumn of each year, while the other half was left fallow (i.e. not planted with crops), to allow the soil to ‘rest’. The Romans developed the three-course rotation, which was in use from the Middle Ages until the 18th century. A three-year cycle was followed on each of three fields, with an autumn-sown crop such as rye or winter wheat, a spring-sown crop such as oats or beans, and a year of lying fallow. Two out of three fields were thus in cultivation every year. The three-field system succeeded only in countries with mild climates, such as England. With the AGRICULTURAL REVOLUTION and the acceleration of ENCLOSURES in the 18th century, more scientific methods were applied to crop rotation. A four-course rotation was adopted based on turnips, clover, barley, and wheat. The introduction of root-crops (such as turnips) improved the soil and hence the quality of harvest and livestock; they also smother the weeds that have grown between plants of the previous crop. The replacement of the fallow with a leguminous crop, such as clover, peas, beans, or lentils, boosts the fertility of the soil since leguminous plants are able to ‘fix’ atmospheric nitrogen, which enriches the soil when they die.