Irrigation decisions

Generally, common approaches in irrigation decisions entail timer-based, sensor based or model-based irrigation control methods.

a. Electrical timers

• Electrical timers specifically designed to control irrigation valves are used.
• This operation is the cheapest, simplest and easiest approach for triggering irrigation events.
• However, time-based irrigation needs skilled personnel and knowledge to compile a present irrigation schedule.

b. Sensor-based control

• Sensor-based control depends on the measurement of the water status either in the substrate (i.e.tensiometer, frequency domain reflectometer) or in the plant (i.e. sap flow meter, thermal sensing)

c. Model-based control

• Model-based control is based on the estimation of plant water loss related to one or more environmental variables (i.e. temperature, solar radiation).
• Scheduling is computerized to obtain in real time crop irrigation needs based on the data provided online by sensors.
• Many methods are available for the estimation of evapotranspiration and most of them use either a modified version or a combination of models originally developed by Penman and Monteith.
• However, the application of these models in commercial practice needs appropriate calibration for each crop