A single controller normally irrigates a size of a field covered by a single valve.
In practice there are various consideration that dictates what actually is the
size of a plot that is controlled by a single valve: technical consideration can
limit the size of a plot (i.e. rate of water delivery), topography limitation and
uniformity of soil and plant size. Where there are no limitations on plot size, a
single controller/valve can irrigate as much as 20 ha.