Turf - Proper Irrigation

Hot, dry weather is upon us. For those property owners with lawns receiving irrigation, it is important to know how to irrigate properly. Turf and landscape professionals installing irrigation systems should take time to educate their clients on proper irrigation. The following is and article on the subject.

Water is essential for turf growth. It is required for germination, photosynthesis and as a part of the turf. Most of the water absorbed by turf is transpired through the leaves into the atmosphere. This water moves nutrients from the soil into the plant, but equally important, it eliminates heat buildup from solar radiation.

The water applied by an irrigation system will evaporate from the soil and be transpired from plant surfaces. Evaporation and transpiration (evapotranspiration) depend mostly on the climate around the plant, thus, the amount of water used by turf changes with the seasons. Because of this, for a well-managed turf, irrigation frequency should change with the time of year.

Only water that is in contact with the roots can be absorbed by the plant. The volume of soil where water can be stored is as deep as the roots are. Root depth is affected by mowing, fertilizing and irrigation practices. A well-managed turf system will develop most of its roots in the first 12 inches of the soil. Another important property of the soil reservoir is that soils have a limited ability to store water. The larger the pores in the soil the less water the soil will hold. Sandy soil hold much less water than loam soils.

Two questions must be answered when scheduling irrigation:

WHEN DO I IRRIGATE?

Water should be applied to turf only when soil-water in the root system has been depleted to an unacceptable level, usually by 1/2 to 2/3 of the stored soil-water. There are several ways to determine when the soil-water reservoir has been depleted beyond an acceptable level. These are:

Visual inspection of the turf . Becoming familiar with the way that turf reacts when water is becoming scarce in the soil is a common method of deciding when to apply irrigation. Common symptoms of water stress include leaf color changes to a bluish-gray tint, footprints that linger long after being made, and curled or folded leaf blades.

Estimations based on climatic records . Past history of climate can be used to estimate how often irrigation should be applied to turf. Tables are available that show the expected number of days that soil water will last for a certain texture of soil.

Direct measurement of soil moisture . Using sensors for measuring the amount of available water in the soil is another way to determine when to irrigate. One such sensor is the tensiometer. As the soil dries, water moves out of the tensiometer through the ceramic, causing a suction that is measured by the vacuum guage. Other moisture sensors are also available and systems can be automated using these sensors.

HOW MUCH WATER SHOULD I APPLY?

The quantity of water applied to turf should not exceed the amount required to refill the soil occupied by the root system (poor quality water may require higher volumes for leaching). Regardless of the time of year, for an established turf the quantity of water applied at each irrigation should always be the same. Irrigation will not be required as often during low demand periods. Typical Delaware soils will be able to hold at least 1 inch of water per foot of soil. The amount of water to apply to a one-foot-deep soil water reservoir, which has been depleted to 50 percent and has a water holding capacity of one inch per foot (1"/ft), is 2/3 of an inch of water.
This assumes an irrigation efficiency of 75 percent. The total volume required will depend on the size of the area being irrigated and the soil-water holding capacity. It takes 620 gallons of water to apply one inch of water to 1000 square feet of an area.

APPLYING IRRIGATION

In order for irrigation to be successful and efficient, the volume of water applied must be measured. There are several ways to measure irrigation volumes of water.

Using a water meter . In a permanently installed system a water meter should be included as part of the irrigation system. In systems that are connected to an urban water supply, the meter installed by the service company can be used. The time required to apply the necessary water can be easily determined by observing the water meter to measure how much water is applied by the irrigation system in a minute. For example, a system that requires 1200 gallons is turned on, and from the meter it is observed that 12 gallons per minute are being used. Thus, the time that the irrigation system should be turned on is 100 minutes (1200 gallons divided by 12 gallons per minute).

Measuring the depth of water applied . When a water meter is not available place five wide- mouth, flat-bottom cans spaced equally along the diagonal of four sprinklers. After 20 minutes of irrigation, turn the system off and use a ruler to measure how deep the water is in each can. Average the five measurements and use the average to determine the time required to apply 2/3 of an inch of water. For example, if a 20-minute can test resulted in an average water depth of 1/2 of an inch, the time that irrigation system should be turned on in order to apply 2/3 of an inch of water is obtained from is 27 minutes. Any water applied after 27 minutes will be wasted as deep percolation.

If a hose and sprinkler is used with this method, set the sprinkler pattern to 1/4 of a circle before carrying out the test. Move the sprinkler to each corner of the irrigated area and irrigate for five minutes from each corner for a total of 20 minutes. When irrigating the turf, apply water for the irrigation duration when the hose-and-sprinkler is used in full circle; for 1/2 the irrigation duration when the hose-and-sprinkler is used in half circle; and for 1/4 the irrigation duration when the hose- and-sprinkler is used in quarter circle. Also, if possible, carry out the test in the early morning hours and under no-wind conditions.

Using automatic shut-off values . A variety of automatic shut-off valves are available that are especially suited for irrigating with a hose and sprinkler. These allow the user to set a time period or volume to apply. These are inexpensive and convenient and reduce water waste due to lack of attention to hose-and-sprinkler systems.

Using soil-moisture sensors . When permanently installed irrigation systems are run using timers, sensors can be used to control these systems. The timer should be set to irrigate every day to apply about 1/3-1/2 of an inch of water during early morning hours for best efficiency. The moisture sensor will allow irrigation only if water is required.

Adapted from "Turf Irrigation for the Home" by F.S. Zazueta, A. Brockway, L. Landrum and B. McCarty, University of Florida.