Features

Hydrozoning Is Focal Point
Of Efficient Irrigation Systems

By Robert E. Reaves

Make sure you know as many facts as possible about the growth characteristics and water requirements of plant materials in your area.

The landscape irrigation market is booming, a reflection of our nation's strong economy. Unfortunately, "cookie cutter" irrigation systems continue to sprout up everywhere like weeds. This results in irrigation system with poor distribution uniformity, with little or no hydrozoning and incorrect sprinkler or drip product choices. For an irrigation system to be outstanding, it's not just the installation of quality irrigation products. A great system is a hydrozoned irrigation system.

Hydrozoning divides a landscape irrigation system based on different plant water requirements, plant height and plant density. Correct hydrozoning starts with a good understanding of the relationship between irrigation systems, soil type, plant materials and irrigation product selection.

For example, the choice between sprinklers and drip often comes down to the height of the shrubs at maturity or the size and location of the planting area. If the plant material will exceed three feet high when mature, you've reached your maximum height to use sprinkler risers.You'll want to consider another choice, such as bubblers, microsprinklers, drip tubing or sprinklers with low-angle nozzles.

New advances in drip irrigation irrigation, such as pressure-compensating emitters or microsprays, make it an excellent choice for many locations. Unfortunately, drip irrigation systems are often abandoned after a few years because of extensive clogging brought on by poor maintenance. Still, drip systems are very successful where the irrigation contractor or landscape maintenance firm understands the importance of routine drip maintenance.

As a landscape contractor, it is imperative that you keep abreast of the new sprinkler and controller products available. With all the great computer design programs on the market, you can know the performance capability of any given sprinkler for a specific design situation. Stay aware of new technology advances by attending IA classes, as well as irrigation manufacturer and distributor programs.

"When selecting irrigation equipment and nozzle sizes, it's helpful if the application rate of the sprinkler head matches the intake rate of the crop cover/soil combination. With certain soil types and sprinkler head combinations, this is not possible. For instance, a clay soil combined with pop-up spray heads is not recommended. Clay soils have a very slow infiltration rate at less than 0.15 inches per hour, while the pop-up spray head has an average application rate or precipitation rate of 1.5 inches per hour," says Larry Keesen in his textbook entitled, "The Complete Irrigation Workbook."

Hydrozones Equal Efficient Irrigation

Hydrozoning is a key component of a water-efficient irrigation system. Some of the factors that determine a hydrozone include the infiltration rate of the soil, soil type, slope, sun exposure and water needs of the plant materials. By using controllers with multiple run times (cycle and soak) and dividing the landscape into hydrozones, each area will receive the amount of water it needs without puddling or runoff.

Why is it so important to understand the relationship of soil type to irrigation design and scheduling? Because once you understand the water holding capacity of the different soil types, you'll be able to schedule irrigation run times without water runoff. "Sprinkler heads with a precipitation rate of one inch per hour have a maximum irrigation run time in bare clay soil of eight minutes. On the other hand, 18 minutes of runtime is acceptable for loamy soil before runoff occurs, " says Keesen. "With a turf crop cover, a maximum run time of five minutes for clay soil and 10 minutes for loamy soil is recommended. Repeat the cycle after 30 minutes if additional water is needed."

Without hydrozones and a system that considers soil infiltration, the most likely scenario is overwatering and water runoff. While serving as extension horticulturist for the Oklahoma State University Extension Service. I quickly learned, the most common reason for plant death is overwatering. However, there are exceptions where underwatering is the problem. For instance, for slopes greater than 4:1, the top will dry out more quickly and will need more water. Use a separate hydrozone for the top of the berm.

Always remember that the water requirement of turfgrass is much different than trees, perennials or annuals. If all these plant types were irrigated under the same hydrozone, it would be impossible to provide the correct amount of water. Make sure the customer understands this basic concept when he or she questions the cost of your services.

Unfortunately, large numbers of irrigation systems installed at new subdivisions around this country (and even some commercial sites) offer little in the way of hydrozoning. These systems are frequently installed by low-bid contractors who install in volume for real estate developers. It's a "hard sell" to convince a real estate developer to fork out the additional cash for better irrigation systems. Perhaps a solution is to get involved with property manager/real estate associations and make presentations on irrigation.

In the residential irrigation market, most homeowners simply aren't willing to pay the cost of running extra laterals to independently irrigate shrubs with a sprinkler or drip system. This is another reason why inadequate irrigation systems continue to be installed and why many contractors avoid the residential market.

Things are better in the commercial irrigation market, especially from the design standpoint. Unfortunately, the maximum benefit of hydrozoning is often not obtained. Property managers and landscape maintenance firms frequently do not understand the concepts of multiple run times. They often set the irrigation system and never make adjustments on run times based on climate or plants.

Plant Material Selection and Spacing

If you've ever worked as a landscape contractor, you know it is a common practice to pack the plants to make the landscape look good immediately after installation. Try to avoid this practice. When the plants mature, you'll only end up removing crowded plants. Make sure you know as many facts as possible about the growth characteristics and water requirements of plant materials.

Seasonal changes in annual beds at commercial sites will require modifications in the irrigation system run times. For example, the water requirements of pansies in the fall and winter are less than zinnias in the summer months. There's also a consideration of the best irrigation system to use. For example, for annuals subject to leaf diseases, bubblers and drip irrigation are probably a better choice than overhead sprays. However, most plants tend to perform and look better with sprinkler irrigation.

Take the time to learn about plant materials that perform best in your area, along with their growth habits. Good communication between the landscape designer, irrigation designer, irrigation contractor and the customer is essential. Get the big picture. A thorough understanding of the relationship between irrigation systems, plant material selection and soil should provide results you can brag about.

"The Complete Irrigation Workbook" can be ordered from The Irrigation Association's bookstore. Contact the IA at (703) 573-3551.

Robert Reaves is editor of Irrigation Business & Technology.

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