The Volok Reform[1] (Lithuanian: Valakų reforma; Belarusian: Валочная памера; Polish: reforma włóczna) was a 16th-century land reform in parts of the Grand Duchy of Lithuania (Lithuania proper, Duchy of Samogitia and parts of White Ruthenia). The reform was started by Grand Duchess Bona Sforza in her possessions to increase the revenues of the state treasury but soon was expanded statewide and was copied by other nobles and the Church. The reform increased effectiveness of agriculture by establishing a strict three-field system for crop rotation. The land was measured, registered in a cadastre, and divided into voloks (land unit of about 21.38 hectares (52.8 acres)). Volok became the measurement of feudal services. The reform was a success in terms of the annual state revenue that quadrupled from 20,000 to 82,000 kopas of Lithuanian groschens. In social terms, the reform and the accompanying Third Statute of Lithuania (1588), promoted development of manorialism and fully established serfdom in Lithuania which existed until the emancipation reform of 1861. The nobility was clearly separated from the peasants which severely limited social mobility.