Irrigation Practices to Preserve Water Quality • E0009TURF
K. W. Frank • G. T. Lyman
Watering the lawn is a necessary activity for many homeowners who desire a high quality turf. When done correctly, irrigating turf will ensure better density and growth that allows the turf to compete more effectively with weeds and to reduce other pest problems. A healthy turf can offer outstanding protection of water resources by significantly reducing surface runoff and soil erosion and increasing the infiltration rate of water into the soil. The first watering event after a fertilizer or pest control application is the most critical when considering environmental impact. Excessive water after application has a much higher potential to move these products past the active plant growing zone in runoff or leachate. By imposing a light irrigation (0.2") after application, these products will be moved into the thatch and root zone where they are intended. Once there, the potential for them to move off the site is significantly reduced.
Understanding a few basics of turf growth and the effects of supplemental irrigation can help determine the best approach for your property. The major factors involved in proper irrigation are the desired level of maintenance, soil conditions, the water delivery system, weather conditions, and the timing of water application.
Basics of Turfgrass Growth
The natural cycle for cool-season grasses found on Michigan lawns has two distinct growth peaks during the year. The first is in the spring when growth increases rapidly following winter dormancy. Characteristic warming temperatures and abundant rainfall during this period promote vigorous growth. Depending on weather conditions, this first growth surge will peak during May or June. Following this period in July and August, weather patterns usually provide high temperatures and low rainfall. Cool-season turfgrasses respond by reducing leaf and root growth during this time. Extended periods of warm, dry conditions will cause the turf to go dormant (stops growth and turns brown). This is a natural process that allows the plant to survive these conditions. The crown of the plant (which is the critical growing point) remains alive - waiting for adequate water. Supplemental irrigation during this period can prevent dormancy and allow the turf to remain green throughout the summer stress period. During late August through October, leaf growth increases with the return of cooler temperatures and more frequent rainfall. Root growth during this period becomes more active and continues into the fall while soil temperatures remain above freezing. The late summer/early fall period is considered the second growth peak of the season. Weather conditions each year determine the duration of the active or dormant growing conditions.
Setting objectives for your lawn and the level of maintenance to which you are willing to commit is the first step in determining your irrigation practices. If you desire a high quality lawn and have an in-ground irrigation system, this goal will be easier to achieve. Medium or low maintenance lawns would not normally be irrigated, and would be expected to go dormant in the summer during the hot, dry periods. Variation in weather patterns from year-to-year will determine the amount of water necessary to maintain a high quality lawn. It is important to note that an abrupt change in watering practices from regular irrigation to no irrigation during the heat stress period might be harmful to the turf. Dormancy must be induced gradually to condition the grass plant to tolerate the onset of hot and dry conditions. The cost and availability of water in your area should also be considered when setting your irrigation goals.
The amount of water required by a lawn is influenced by soil type. Sandy soils hold less water than loamy soils, so the turf dries out faster in sands. Low volume, frequent applications insure that excessive water doesn't move past the plant zone. Soils with more silt and clay or organic matter can hold more water per application. However, compacted clay soils do not accept water readily and runoff can occur from sloping sites. The goal is that the delivery rate of the irrigation system should never exceed the infiltration rate of the soil.
Amount of Irrigation
Generally, cool-season lawn turf requires 0.5 to 1.5 inches of water per week. The amount of water you apply will vary depending on the weather conditions and rainfall events. Periods of high temperatures, coupled with full sun and high wind will require more water. It is important to note that the water can come from either rainfall or irrigation. Light, frequent applications of water are much more productive than heavy (soaking) applications once a week. Remember that turf roots are naturally shorter during hot and dry weather and water moved past the root zone is wasteful and of no benefit. Research at Michigan State University indicates that damage from certain turf diseases and insects are reduced when light, frequent (daily) irrigation is used compared to a heavy, infrequent irrigation. Light, frequent irrigation corresponds to 0.1 to 0.2 inches of water for each irrigation event. Applying this amount could correspond to 10-60 minutes of irrigation depending on the output of your system. The delivery rate and pattern of your irrigation system can be measured by scattering rain gauges, Tupperware containers, or tuna fish cans throughout the lawn prior to an irrigation cycle. Turn on the system for one hour and measure the amount water collected in each container. Use this information to determine how long it will take to provide the amount needed. An in-ground irrigation system is more expensive, but will give better coverage and is easier to use. Hose end sprinklers are not as easy to use and uniform coverage is a challenge.
Timing of Irrigation
The light, frequent irrigation treatment that was researched at MSU was applied in the early afternoon just prior to the highest daytime temperature. The early afternoon timing takes advantage of the cooling effect a light application of water has on the turf. During warm, dry summers in Michigan many local water authorities may limit home lawn irrigation to alternating days throughout the week or to specific time periods thereby making a light, daily irrigation application impractical. Additionally, high winds during the day at some locations may make light, frequent irrigation during the early afternoon less effective. When water restrictions are imposed, light, frequent irrigation could mean irrigating every other day or even every third day. The concept is still the same; to produce a high quality lawn it is best to apply smaller amounts of water more frequently than to apply a large amount in one irrigation event. In these circumstances irrigating from midnight until 6 a.m. is acceptable. Recently the Detroit Water and Sewage Department instituted a policy to encourage homeowners to irrigate between midnight and 6 am and to avoid irrigating between 6 am and 9 am. Irrigating between midnight and 6 am can be very effective as it reduces the time the turf remains moist during the over-night period and may also be a time of little or no wind. In contrast, irrigating during the early evening hours is one of the worst times to irrigate as this results in the turf remaining moist for an extended period of time and may increase disease activity.
Wrap It All Together for Success
First, choose a level of quality or maintenance for your lawn that is compatible with your objectives and choose a range of total water needed (0.5-1.5 inches per week). Determine the specific amount you wish to apply after making adjustments for weather and soil conditions. Split the desired amount up into light frequent events.
Be aware of poor distribution when irrigating during periods of high winds. Additional irrigation cycles may be needed to achieve adequate distribution and prevent dry spots. On sloping lawns, using shorter cycles with repetition will permit time for infiltration and reduce the potential for runoff.
Finally, take control of the sprinkler! Coordinate irrigation with rain events and don't overload your lawn by irrigating in the rain. Install a rain over-ride device on your irrigation system to prevent wasting water. During rainy periods turn off a clock-controlled irrigation system. Remember that keeping the water where the turf can use it is the most efficient and environmentally sound program.