SCHEDULING THE IRRIGATION SYSTEM FOR OPTIMUM TURF QUALITY

By

Larry Keesen

Overwatering occurs on most turf sites around the country that we have audited and evaluated. I shudder when I think of the huge waste of this precious resource and the potential environmental damage from irrigation system runoff and damage to structures and pavement.

When contractors install a new irrigation system, the initial irrigation schedule is set for total saturation or the "rice paddy effect." Additionally, many contractors and designers fail to provide the owner with proper scheduling guidelines and techniques or the owner doesn’t take the time to find out about proper scheduling. Hopefully what follows will help you save water and have a better looking lawn.

GETTING STARTED. The first step in scheduling is to determine the application rate of the sprinkler heads for each zone throughout the irrigation system. This can be done as follows:

Place several catchment devices (cans or cups) in the landscape areas of one of the sprinkler system zones to measure the amount of water that the system applies for 15 minutes. Next measure the depth of water in inches in the can and multiply by four. This will be the application rate in inches per hour for each container. If three containers are set in one zone area, and the readings are .5", 1", and 1.5" then add the three together and divide by three and the average application rate is 1" per hour. This rate of application can then be used to calculate accurate irrigation time schedules.

If the sprinkler head application rate is 1.0 inches per hour and 0.50 inches needs to be applied, the runtime for the zone will be 30 minutes (0.50in./1.0-inches = .50 x 60 min. = 30 min.).

TURF WATER USE. Turf water use varies widely through the seasons. One way to predict plant water requirements is to use historical evapotranspiration (ET) data. Historical data is an average of up to 30 years, and is useful for predicting general monthly water requirements. The following are Weekly water requirements in inches per hour for each month during the irrigation season:

Month APR MAY JUN JUL AUG SEP OCT

Inches per week .25" .80" 1.2" 1.7" 1.6" 1.0" .25"

Small radius pop-up spray heads (10 to 15’ spray radius) often have an application rate in excess of 1.5 inches per hour. To avoid runoff and promote more efficient irrigation, the runtimes for pop-up spray heads should be reduced to five to seven minutes with repeat cycles as needed. Most single stream rotor heads have an application rate ranging from .30 to .80 inches per hour. Avoid watering every day if possible. Once a week is enough in April and October while July may require every other day or every third day watering.

WHEN TO WATER. The best time of day for irrigation is between the hours of 9:00 P.M. and 7:00 A.M. for the following reasons:

1. Potential soil compaction is reduced by the absence of foot traffic on wet grass.

2. The ET rate is much lower at night because it is usually cooler, there is less wind (especially in the early morning hours) and little solar radiation.

3. Less water is wasted because of wind deflection.

4. Avoid watering before 9:00 P.M. to avoid fungus problems.

5. At least a ten percent savings in water is achievable by watering at night.

* If you can see your own footprints in the grass you

have just walked on, you need to water!

* Use short run times and several cycle starts per irrigation period and water as infrequently as possible.

* Water between 9 PM and 7 AM to decrease water

loss through evaporation.

* Pay attention to the seasons: Plants need little or no irrigation water through the winter and an increasing amount each month till the demand peaks in July, and begins to taper off each month as the season cools.