Irrigation refers to purposely providing land with water, other than rain, for improving pastures or crop production. Irrigation usually implies the existence of infrastructure and equipment for applying water to crops, such as irrigation canals, pumps, sprinklers or localized watering systems. However, it also includes manual watering of plants using buckets, watering cans or other devices. Uncontrolled land flooding by overflowing of rivers or streams is not considered irrigation. Variate associated annual water from irriagation are expressed in m3/ha/year.
FAO, 2015. World Programme for the Census of Agriculture 2020. Volume 1 Programme, Concepts and Definitions. FAO, Rome.
http://www.fao.org/3/i4913e/i4913e.pdf