Designing irrigation systems that conserve water
Water, sunlight and temperature all influence healthy plant growth, but water is the factor over which landscape professionals can exert the most control. And conserving water is becoming more important every year.
Even in areas where water is plentiful, individual consumption and efficient use are issues getting increased attention. Because of this, landscape professionals and homeowners assume an even larger responsibility in managing this resource.
Huge strides in irrigation system design have enabled landscape professionals to manage water use efficiently. Watering schedules can be as simple or as elaborate as individual situations dictate. Adaptations to an existing irrigation program even can be made automatically through weather station information downloaded to a computerized control system. These technological advances result in more efficient irrigation for the professional and the homeowner.
To call irrigation control systems fully automatic, however, is a misnomer. These systems require input from landscape professionals to determine the location's specific needs. The many variables of plant species, soil conditions, climate and regulatory issues play significant roles in governing the manner in which the systems are designed.
Climate conditions Several climate-related conditions play a major factor in the way you design irrigation systems to deliver water:
Rainfall. You should know the average daily, seasonal and annual rainfall in order to properly select delivery equipment. This information is available through the National Weather Service or other sites on the Internet.
Evapotranspiration (ET). This describes the amount of water lost from the surface due to evaporaton, plus water drawn from the soil by plants (transpiration). Microclimate. conditions in existing hardscapes and landscapes may affect these measurements, as well as climate.
Temperature. A thorough knowledge of seasonal temperature averages and ranges is important for effective water delivery and usage.
The specific site being considered affects the way you design an individual system. These factors include:
Soil type. Percolation rates and a soil's water-holding capacity can vary. Defining these qualities will make for easier design and programming.
Drainage plan. Land-use requirements are key. For example, sports turf must drain more quickly than ornamental turf. Different plant species have different water requirements for proper growth.
Water source. The amount of water available during the peak demand times will dictate some design parameters. Water quality affects not only how you program the irrigation system, but how you manage the plants and soil.
Plant material selection. Select well-adapted varieties. Using plant materials that are difficult to manage can spell failure for the overall effort.
Once these factors are understood, you are ready to specify the delivery system equipment. Designing for peak water efficiency should be the aim of all good irrigation system designers. To that end, landscape professionals should familiarize themselves with the latest in equipment options available.
Fertigation Systems Landscape professionals should consider fertigation, the process of injecting liquid fertilizer into an irrigation system. Fertigation can be a highly efficient way to deliver nutrients, and help develop deeper, thicker root systems. Thicker, deeper roots allow for more efficient water usage which allows the landscape professional or homeowner to gradually reduce water usage. This is particularly true if you use high-quality organic or organically-based fertilizers.
You can inject other materials into irrigation water to modify soil or water, for example. There are organically based pest control, fungus control and other lawn care products that canbe delivered safely through a fertigation system. (Never deliver chemical pesticides, herbicides or fungicides via irrigation water unless the product label clearly specifies this use, and you are sure that all mechanisms to prevent contamination of potable water are operating correctly.)
Numerous irrigation injection systems are available commercially-check with your irrigation equipment supplier.
Pump stations The pump station you choose should suit the needs of the application, be efficient and have the power necessary to deliver the water. For example, variable speed drive mechanisms are becoming common on large-scale pumping stations. They conserve energy by using only the horsepower required to complete the job.
In sites where you're using surface water and you can place the pump station where minimal lift is required to get the water, centrifugal pumps are the best bet. When possible, let gravity decrease power requirements by locating water storage areas at higher elevations.
Low-pressure systems have been successful in applications where infrequent, deep-water cycles are preferred and where system operations are not as restrictive. These systems can conserve energy and water when soil conditions, plant material and land uses permit.
Distribution systems Piping, and system control issues are key elements in building efficiency in your distribution system. By working closely with the designer on the distribution system, you can maintain the original intent of the design and still incorporate water-conserving features into the plan.
The control package can be as specific as the homeowner can afford. The control package offers water conservation through specific area control. Many times, independent head control is deemed too expensive. However, it is the key to accurate and efficient water control. Money spent on the front end results in a better overall product and cost savings down the road.
Design a system that delivers adequate amounts of water to each area of the yard, without over-watering any area. Ornamentals, trees, shrubs and turf require different amounts of water. Consider the types of plants you will grow in each area before determining the size and location of each zone and which heads or drip systems to use. The more specific the system design, the more precisely you can allocate water. This is especially true for fertigation systems. Develop a fertigation system that allows for customized fertilizer and product delivery by zone, so that your system can deliver the proper amount of fertilizer to each landscape element.
Spray heads and emitters Design and operation of irrigation heads are as varied as each situation you may imagine. Manufacturers have been working with this issue for decades. Choosing the appropriate head for an application is important to water efficiency. A designer can assist in laying out the available options.
In certain instances, excessively high spray angles can cause water loss to wind and evaporation. Low-trajectory heads can improve application efficiency. Where foliar applications are not imperative, use drip emitters wherever practical to directly apply water to the soil.
Factors other than irrigation system design also affect irrigation system efficiency. Proper soil aeration and soil conditioning decrease runoff and increase the water penetration into the soil. Adequate mulching decreases water loss from evaporation at the soil surface.
In the end, professional irrigation system designers also must rely on the manager or property owner to provide the parameters for how the system will operate. They will know the most about what the design should include.
As you plan your irrigation systems, look at these and other opportunities to advance water conservation on your sites. Water is a vital resource that can sustain generations to come if we all do our share to take the responsibility for its management.
Stephanie MacLeod, CPAg, CGCS, is director of agronomy for Down to Earth Distribution, LLC, an alternative agronomics supply company in West Palm Beach, Fla. Ned Lips is CEO of FertiGator, Inc., a manufacturer of residential, commercial and institutional fertigation systems.
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