Em4885 irrigation management practices to protect ground water

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CHAPTER 4
Pacific Northwest Extension publication PNW288, Irrigation Scheduling, and WSU Cooperative
Extension publications EB1304, Simple Irrigation Schedule Using Pan Evaporation, EM4825, WSU
Drought Advisory: Scientific Irrigation Scheduling, and EB1513, Irrigation Requirements for Washington:
Estimates and Methodology, offer more complete discussions of irrigation scheduling. Several
Drought Advisories from WSU Cooperative Extension also contain information useful for
irrigation scheduling systems. These include Tree Fruits (March 1988), Vegetable Crops (April1988),
Mint Irrigation Management (March 28, 1988), and Visual Crop Moisture Stress Symptoms (March
1988). Issue 11 (Fall 1989) of The Washington Irrigator also contains a discussion of irrigation
scheduling. SCS National Practice 449 addresses general irrigation water management.
In addition, Washington State University Cooperative Extension has developed PAWS, Public
Agricultural Weather System. PAWS is a valuable source for irrigation management information.
It consists of a network of standardized, calibrated weather stations placed in strategic agricultural
production areas. The data from these weather stations are stored in computers and available to users
of the service. More importantly PAWS calculates a daily estimate of a reference evapotranspiration.
This reference ET is essential for checkbook irrigation scheduling. WSU Cooperative Extension
Bulletin 1547, a PAWS user manual, is available from any Cooperative Extension office.
The PAWS network includes data from the Agri-Met system, a Northwest-wide network of
weather stations and irrigation scheduling information developed and operated by the Bureau of
Reclamation. The Bureau’s Pacific Northwest Regional Water Conservation Center in Boise, Idaho,
has more information on Agri-Met and its services to growers.
Checkbook irrigation scheduling can be complex to start up. Obtain and read the Cooperative
Extension literature cited above. It is best to utilize the services of a competent and experienced
agriculturalist when first starting irrigation scheduling. The local Conservation District, Soil
Conservation Service, or WSU Cooperative Extension office can also provide aid.
Graphical methods of irrigation scheduling are simpler to start up but take some experience to
develop the calibration needed for effective use. Again, it is highly recommended that experienced
consultants be called on when first starting an irrigation scheduling system.
IP 2.01.06 - Practice Total Planning of Individual Irrigations
Objective
Manage the irrigation system and each irrigation objectively to increase
efficiency and develop benchmarks on which to base improvements.
Description
Total planning for individual irrigations involves the following steps:
1. Determine when to irrigate - this is an agronomic decision based on how the
crop is to be managed. The use of soil or plant moisture measuring devices
such as tensiometers, gypsum blocks, and leaf pressure chambers can be valuable
aids in deciding when to irrigate. Irrigations are usually scheduled to prevent crop
stress. However, sometimes crop stress is desirable.