Irrigation scheduling

Irrigation scheduling is the process used by irrigation system managers to arrive at the correct frequency and duration of watering. The various factors involved include the precipitation rate of the irrigation equipment, the soil's infiltration rate, the soil's available water holding capacity, the effective rooting depth of the plants to be watered, the current watering requirements of the plant (which may be estimated by calculating evapotranspiration, or ET), the time in which water or labor may be available for irrigation, and other factors, such as the amount of allowable stress which may be placed on the plant, or timing to take advantage of projected rainfall. For high value vegetable crops, this may mean no allowable stress, while for a lawn some stress would be allowable, since the goal would not be to maximize production. The goal in irrigation scheduling is to apply enough water to fully wet the plant's root zone while minimizing overwatering and then allow the soil to dry out in between waterings, to allow air to enter the soil, but not so much that the plant is stressed beyond what is allowable.

In recent years, more sophisticated irrigation controllers have been developed that receive ET input from either a single on-site weather station or from a network of stations and automatically adjust the irrigation schedule accordingly. When properly set up and maintained, these controllers do tend to conserve water over conventional human scheduling as the program is updated at least daily.

Other devices helpful in irrigation scheduling are rain sensors, which automatically shut off an irrigation system when it rains, and soil moisture sensing devices such as tensiometers and gypsum blocks.