More and more farms are using spray irrigation, rather than flood or border dyke systems, to water pasture and crops. About half of spray irrigators used are centre pivot systems, which pump water from underground aquifers along rotating arms that travel in a circle across the field. The rate of rotation can be altered, and different parts of the arm can be set to apply differing rates of water. A centre pivot arm of 500 metres in length will irrigate about 79 hectares in one rotation.