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AZSCHED irrigation scheduling software, an interactive computer program using near real-time weather data and growing-degree-day based crop coefficients, was developed and tested in Arizona between 1988 and 1991 (Scherer et al., 1990a, 1990b; Clark et al., 1989, 1990, 1991).  The program can read properly formatted weather data files generated by automated weather stations or local weather data can be entered by hand.  Historical weather files which are used for default values and for predictions are needed for each area where the software is to be used.  Soil water holding capacity data, acceptable soil water depletion level, irrigation efficiency and a planting date are needed to activate a field.  Field summaries of 20 fields are viewed on a screen and up to 60 fields can be managed per sub-directory.  AZSCHED is user-friendly, menu driven and minimizes the amount of information that must be input from the keyboard.  The program is designed to be used by farmers and researchers on an IBM compatible personal computer.

Conclusion

The AZSCHED program has been used successfully for scheduling irrigation on cotton at several locations in southern Arizona.  The menu driven software is relatively easy to learn and operate.  Management Allowed Deficiencies and irrigation efficiencies can  be adjusted throughout the growing season as conditions may warrant.  The MAD can be adjusted to match the software to many different irrigation systems.  For example, with a furrow irrigation system, capable of applying 5 to 25 cm of water per irrigation, the MAD might be set between 40 and 60% depletion to trigger an irrigation, whereas a center pivot sprinkler system, capable of applying 0.75 to 1.5 cm of water per irrigation, would need to have the MAD set between 5 and 15%.  As with any irrigation scheduling method, a certain amount of time must be invested to have a successful program.

After the fields are initialized the program should be updated at least weekly with weather, irrigation and rainfall data.  With practice, the weather data can be downloaded from AZMET (the Arizona weather network) and loaded into AZSCHED in less than 15 minutes.  Updating each field takes less than five minutes.  To print out a prediction sheet with all fields listed is almost instantaneous (depending on the speed of the printer).

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