flow of the water to irrigation. It is a binary control variable that
assumes the values of 0 or 1 representing off or on states respectively.
The authors acknowledge that Q1 maybe practically variable.
However, due to its complexity, we have, in this introductory work,
assumed that it is constant.
2.2.2. Constraints
These are the limits that affect the operation of the irrigation
system.
2.2.2.1. Soil water balance. The FAO-56 Penman–Monteith equation
is the standard technique for obtaining reference evapotranspiration,
ET0, whose data is obtained from weather stations.2 Crop
evapotranspiration, ETc , obtained from ET0, results from the various
water inefficiencies in various crops [36]. It is obtained as
ETc ¼ KcET0 ð2Þ
where Kc is the crop coefficient. Irrigation scheduling is meant to
ensure that the soil doesn’t dry beyond a certain threshold [29].