AZSCHED - software for real-time irrigation scheduling

A user-friendly computer based scheduling program was developed to minimize the amount of data which needs to be input by the user by utilizing a network of twenty automated weather stations in Arizona. Irrigation scheduling is performed using a soil water balance approach. The Modified Penman equation is used to calculate reference evapotranspiration and crop coefficients are based on growing-degree-days. These methods make this model highly adaptable to a variety of climatological conditions without loss of accuracy. Accuracy can be compromised through the use of inaccurate inputs by the user. The sensitivity of the model to different user inputs under Arizona conditions are presented, showing that the model is most sensitive to the inputs used for irrigation efficiency and applied irrigation volume. Recommendations for rational use of this method require either measurement of irrigation volumes applied or periodic correction of the soil water balance through field measurements.