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  Computer Software for Irrigation Scheduling
David F. Zoldoske

CATI Publication #900608
© Copyright June 1990, all rights reserved

What's the best way to determine when and how much to irrigate? The old way was to do a lot of field testing, take a look at the weather and the crop, combine that with seat of the pants experience, and make your best estimate. The new way is to load an irrigation scheduling program into your computer, feed it the data, and let it give you some answers.


Other than to impress their neighbors, why should growers use this new technology to schedule irrigation? To put it in a nutshell, because it is a better, more efficient way to operate.

Many growers who do not use crop related irrigation scheduling often over- or under-irrigate. This can reduce the profitability of any farming operation. The cost of over-irrigating includes additional water, higher fuel or electricity use, more pump maintenance, more labor, and increased drainage and possibly salinity problems that can eventually lead to yield reduction . Under-irrigation reduces yield and quality, and can lead to total crop loss.

Additional costs come in the form of downtime when irrigation conflicts with spraying, harvesting, or other cultural practices.

The cost of over-irrigating includes additional water, higher fuel or electricity use, more pump maintenance, more labor, and increased drainage and possible salinity problems that can eventually lead to yield reduction.

Computer aided irrigation scheduling is a process that uses field measurements to predict irrigation needs and schedule irrigation. Field measurements or data come in a variety of forms.

Soil moisture level, for example, can be measured by soil feel test, where the soil type and grower's experience will indicate the relative amount of moisture in the soil. Soil moisture measuring devices, such as tensiometers or electrical resistance blocks, could be used instead. This data is used by the computer to schedule irrigations, and to verify computer-predicted soil moisture levels.

Daily or weekly weather data is used to compute the plants' evapotranspiration (ET) rate. The ET rate is a combination of water loss from cropped area into the atmosphere from two sources: evaporation from the soil (E) and transpiration from the plant surface (T). The ET information is used to predict crop water requirements.

The reference ETo figures are delivered to the ATI-Net system through computer linkup with the California Department of Water Resources in Sacramento. The DWR's California Irrigation Management Information System (CIMIS) obtains the figures daily from more than 60 computerized weather stations located around the state.

ETo and other information provided by ATI-Net is available to the public at no charge. Linkup to the system requires a microcomputer or terminal with communications software and a modem installed on a telephone line. Depending on the user's proximity to one of 20 CSU, Fresno campuses, there may be toll charges for use of the phone lines.

For more information on ATI-Net call (559) 278 4872.

Additional information may include crop stress curves, which are used to identify the point where economic damage begins to occur in the plant. These crop stress curves can be adjusted for poor water quality (e.g., salinity).

The irrigation program will schedule irrigations to maintain maximum economic potential. The field measurements are correlated to specific fields, acreage size, soil type(s), crops, irrigation methods, irrigation efficiency, salinity problems, and historical weather data.

Using this wealth of information, the computer program is able to sort out and schedule irrigation frequency and amount. Further allowances for cultural or timing conflicts can be used to modify the irrigation schedule.

The computer program produces a written report or recommendation on when and how much to irrigate. This report should include the length of time a pump or valve needs to operate or the gross amount of water which needs to be applied and the day the irrigation should begin . The report will list the fields according to irrigation priorities.

Many of these reports allow for a written comment section for verification of soil moisture levels or other pertinent data.


The hardware generally required to operate an irrigation scheduling program includes a personal computer complete with keyboard and two disc drives (or one disc and one hard drive), monitor (color optional), and a dot matrix or laser printer. The price of a basic computer starts around $600 or $700, with the monitor and printer costing another $300 each. Additional hardware might include a phone modem that allows the computer to access local weather information or a weather station located on your farm.

As for irrigation scheduling software programs, you will need to spend time surveying the various packages available. Talk with growers, farm advisors, and others in your area who have experience with scheduling software. This will provide several benefits: a more thorough understanding of how a software program works; an idea of relative ease of operation; and an idea of the cost of software (some start around $500).

Furthermore, find out about the software vendor's reputation. Consider the technical support for software installation and maintenance, and the cost of upgrading your current software as newer versions are made available.

You will probably want a program that uses your current method of scheduling as well as offering the advantages of other techniques. Since irrigation systems and methods vary widely, it's important that the program be flexible enough to meet your needs. You may also want to check with your local cooperative extension office or university for class offerings on selection and uses of scheduling software. Finally, one should ease into computerized scheduling by continuing with your past irrigation practices until you gain confidence with the computer's recommendations.

Once you have come to depend on an irrigation scheduling program, you may wonder how you ever lived without it. If you want complete automation, many irrigation scheduling programs can be connected directly to a central controller. This allows for direct control of irrigation in the field. This is generally best suited for pressurized irrigation systems (sprinkler, micro-irrigation, or drip).

Some benefits derived from this arrangement are the continual updating of water needs and eliminating the need to handle and reenter data. However, automation is never a substitute for getting out in the field and monitoring the crop.

The table below shows a computerized irrigation projection from a typical software package. The sample printout is from the ROY irrigation scheduling program, courtesy of Orange Software, Fresno, California
Irrigation Date (mm/dd/yy) Applied Net Depth Gross Duration (hh:mm) Set Volume (1000g) Flow (cfs) Stress (%) Root (feet) Crop Coeff (%) ET (inches) Stage Name CM Level (%) CM Defic (in) CM Resv (inches) Cycle in Days
6/23/86 2.86 3.36 11:10 731 2.43 10.8 4.00 65.30 0.16 LATE 60.30 2.86 7.20 26
7/11/86 2.75 3.23 10:50 703 2.43 10.3 4.00 64.40 0.16 LATE 61.80 2.75 7.20 18
7/30/86 2.84 3.35 11:10 727 2.43 10.7 4.00 63.40 0.15 END 60.50 2.84 7.20 19
8/20/86 2.78 3.27 10:50 711 2.43 10.4 4.00 62.30 0.13 END 61.40 2.78 7.20 21
9/14/86 2.8 3.29 11:00 715 2.43 10.5 4.00 60.90 0.11 END 61.10 2.80 7.20 25
10/17/86 2.85 3.35 11:10 728 2.43 10.8 4.00 59.10 0.08 END 60.40 2.85 7.20 33
12/13/86 2.88 3.38 11:20 735 2.43 10.9 4.00 56.00 0.04 END 60.00 2.88 7.20 57
12/31/86 ------At Cutoff Day----- 2.05 4.00 55.00 0.04 END 91.10 0.64 7.20 57