IRRIGATION: THE KEY TO MAXIMIZING TURF PRODUCTIVITY

Transcription

1 IRRIGATION: THE KEY TO MAXIMIZING TURF PRODUCTIVITY

2 Today s turfgrass producer understands the importance of proper water management, not only in seeking a competitive edge, but in maintaining the stewardship of his resources. For these reasons, determining when and how to irrigate is the key to obtaining a profit and is often the most important single factor for success. ACHIEVING THE RIGHT BALANCE Determining and delivering the right level of irrigation is critical to the health of turfgrass and to the preservation of water quality. Underirrigating produces stressed and nonproductive plants. Overirrigating increases the potential for leaching or surface runoff; it also weakens the turfgrass making it more prone to pest attacks and environmental stress. Achieving the right balance between the two is a matter of interpreting plant needs and selecting an irrigation system which can provide efficient response. EVAPOTRANSPIRATION (ET) Understanding evapotranspiration helps turfgrass producers schedule irrigation needs. The evapotranspiration (ET) process is the combination of two separate processes: Evaporation of water from the soil surface or from the crop surface (intercepted water or dew) Transpiration of water from plants to the atmosphere Evaporation of moisture from the soil and leaf surfaces is directly related to temperature, humidity and wind speed. It plays an important role in determining additional water requirements. Transpiration is the last step in a process that starts with water entering the roots, moving through the plant stems and leaves and escaping through pores (stomata) in the leaves. The rate of evapotranspiration is affected by: Weather Plant type or species Stage of growth of the plant Since ET is directly related to the quality and quantity of the turfgrass produced, the goal for irrigation management is to select a system which can efficiently supplement rainfall with just enough water to meet the full ET requirement. ET information is critical for establishing water management plans and for establishing: System designs, including application rate and flow rate Irrigation scheduling Salinity control Complex equations have been developed by irrigation engineers to aid in the planning of irrigation schedules. These equations have then been converted to reference charts that are available in most turf growing areas. Since weather can vary drastically from one location to another, ET values may vary slightly in a given region of a state. Small changes in temperature or wind speed, for example, will not change the relative index.

3 Local information on evapotranspiration (ET) is available from many on-site weather stations or public weather networks to aid turfgrass professionals with irrigation management decisions. Proper utilization of ET information can provide accurate estimates of daily water needs. Information on evapotranspiration references is available via the Internet at WATER REQUIREMENTS In general, most turfgrasses need about 1 inch (2.5 cm) of water per week to maintain normal growth and color. Grasses that are shallowrooted or heavily fertilized will use up to 2 inches (5.1 cm) per week. Water use rates depend upon: Soil type Grass species or cultivars Turf management levels Atmospheric conditions SOIL TYPE Water infiltration rates and retention rates vary with the sand and clay content of the soil. An application of 1 inch (2.5 cm) of water will wet a clay soil to more than 4 inches (10.2 cm) deep, a loam soil to 8 inches (20.3 cm) deep, and a sand soil to more than 15 inches (38.1 cm) deep. The information presented in Figure 1 demonstrates this wetting capability. Figure 1. Water Applications. (Example: 1 inch [2.5 cm] of water will wet a clay soil to more than 4 inches [10.2 cm] deep, a loam soil to 8 inches [20.3 cm] deep, and a sand soil to more than 15 inches [38.1 cm] deep.) Depth of Soil Wet (inches) 0 3 (7.6 cm) 6 (15.2 cm) 9 (22.9 cm) 12 (30.5 cm) 15 (38.1 cm) Amount of Water Required (inches) (2.5 cm) (5.1 cm) (7.6 cm) (10.2 cm) LOAM CLAY 18 SAND (45.7 cm) Source: Turfgrass Water Management, Leaflet 399, The University of Georgia College of Agricultural and Environmental Sciences, Clay soils or fine-textured soils are the least desirable for turfgrass production. Since they absorb water slowly they require more water to obtain uniform soil moisture levels and will stay wet for extended periods. This requires slower, more extended irrigation. Sod raised on clay soils is heavier to haul than sod on muck or lighter soils. In addition, mowing and harvesting schedules must be adjusted before equipment can be run over the sod. Poorly drained fields are unsuitable for sod production. Muck soils are the most desirable soils for raising sod. They have good water holding capacity, less bulk density versus sandy or clay soils, so they weigh less and are cheaper to transport. Sandy soils are generally not recommended for sod production. Maintaining adequate soil moisture is difficult and even though these soils absorb water much faster than clay or finetextured soils, they retain less water and therefore need more water to maintain adequate moisture levels. WATER REQUIREMENTS OF DIFFERENT GRASS SPECIES Water requirements among different grasses reflect differences in the daily evapotranspiration rates, root depth, viability and quality, and drought resistance. Generally, turfgrasses with high water use rates tend to have low drought tolerance. Frequently used warm season turfgrass species include: bahiagrass, common and hybrid bermudagrass, dichondra, kikuyugrass, St. Augustinegrass, zoysiagrass. Cool season turfgrass species include: annual and perennial ryegrass, bentgrasses, fescues, Kentucky bluegrass. Some turfgrasses, like bermudagrass, develop deep root systems to obtain the needed water. Other turfgrasses, like some zoysiagrasses, have shallow root systems and need more frequent irrigation to remain green. Warm season turfgrasses require less irrigation than cool season turfgrasses to maintain growth and color. ENVIRONMENTAL CONDITIONS Environmental conditions that favor the occurrence of most turf diseases include periods of high humidity, rain, heavy dews or fogs and warm temperatures. Turf is the most susceptible during periods of rapid growth. Pythium normally occurs in poorly drained areas where water

4 stands. Brown patch also occurs in wet areas and is most pronounced in spring and fall months when grass growth is slow. Grey-leaf spot disease of St. Augustinegrass normally occurs during hot, humid weather. Irrigation scheduling is a critical tool to manage or prevent diseases from becoming established. Figure 2. Ensuring that Seedbeds Stay Moist IRRIGATION MANAGEMENT AND TIMING Proper timing and an adequate amount of irrigation are necessary for optimum growth, maximum quality, and best appearance of the respective turfgrass species. This makes it important to select an irrigation system which provides maximum flexibility and precision. Although labor and production schedules may dictate irrigation timing, before sunrise is considered the best time to irrigate because of low wind and cooler temperatures. Research shows water losses at night from irrigation are 50% less than from midday irrigation. Additional studies show that irrigating after dew has dried from the morning sun or wind may extend the period of free surface moisture and enhance disease development. WATER REQUIREMENTS DURING GERMINATION The period of seed germination is a critical time for water management. Seeds must absorb about 50% of their weight in water before the germination process can proceed. Irrigation system travel speed must be sufficient to keep seedbeds moist for germination. To provide this, center pivot and lateral move systems can be equipped with high-speed center drive motors. In addition, sprinkler packages can be custom designed for each system to minimize evaporation and match soil infiltration requirements. To achieve a high rate of germination and good seedling emergence, it is important that supplemental irrigation be capable of keeping the seedbed moist. This will minimize stand losses that can occur from soil drying and provide more efficiency from preemergence herbicides and fertilizers. For grasses that are established from sprigs, keeping the area moist until all the sprigs have rooted (approximately 7 to 14 days) or until the seedlings are 1 to 2 inches (2.5 to 5.1 cm) high will ensure that grasses, such as bermudagrass and zoysiagrass, get off to a good start. Table 1. Evapotranspiration Rates of Cool and Warm Season Grasses Cool Season Grasses Evapotranspiration Rates (in. water/day) Warm Season Grasses Evapotranspiration Rates (in. water/day) East West East West Kentucky bluegrass.146 (.37 cm).210 (.53 cm) Bermudagrass.123 (.31 cm).199 (.51 cm) Perennial ryegrass.146 (.37 cm).253 (.64 cm) St. Augustinegrass.131 (.33 cm).223 (.57 cm) Tall fescue.143 (.36 cm).270 (.69 cm) Zoysiagrass.139 (.35 cm).233 (.59 cm) Source: Adapted from TPI Turf News: March/April 1997.

5 WATER REQUIREMENTS FOR ESTABLISHED TURFGRASS After establishment, managing turf requires attention to: Nutrients Cutting schedules Pest management Water management After the seeds have germinated and rooting has taken place, the goal of proper irrigation is to wet the soil to a depth just below the existing root zone to encourage further rooting. Deeper watering does not benefit the plant and can potentially leach contaminants into the groundwater. Shallow watering causes roots to proliferate near the soil surface and reduces drought resistance and weakens the turf. Turfgrass must receive adequate water in a timely manner throughout the season. As a general rule, apply enough water to soak the soil to a depth of 6 to 8 inches (15.2 to 20.3 cm), which is usually equivalent to about 1 inch (2.5 cm) of rainfall or 27,150 gallons (102,771 L) per acre. Water infiltration and holding capacity varies with soil type. To wet the soil to a depth of 6 to 8 inches (15.2 to 20.3 cm) requires 0.5 inch (1.3 cm) of water in sandy soils, while a clay soil needs 1.75 inches (4.5 cm). The creation of wet spots in fields because of poor soil aeration and overwatering can weaken the turf, cause root diseases and invite the invasion of shallow-rooted weeds such as crabgrass, annual bluegrass and oxalis. Dry areas in the field will cause poor color of turfgrass and may allow the invasion of deep-rooted weeds such as bermudagrass, dandelions, plantains, clover, knotweed and yarrow. FERTILIZATION Proper fertilization is required in order to produce vigorous, dense turfgrass. Low fertility (especially nitrogen) produces thin stands that can be easily invaded by weeds. Monthly applications of nitrogen are needed in areas of turf production to produce quality turfgrass. The type of turfgrass grown will determine the amount of nitrogen needed. Table 2 lists several turfgrasses grown in California and their respective nitrogen needs per month. IRRIGATION SYSTEMS Growers who demand uniform production schedules to meet market needs have moved away from traveling guns to more controllable systems such as the center pivot and lateral move. In choosing the type of system, the following considerations should be made: Peak turf water requirements and timing of the applications Shape and size of the field to be irrigated Topography of the field The amount of time and labor available to operate the system Well capacity and pumping ability of the system Water regulations THE IMPORTANCE OF SPRINKLER SELECTION Improvements in sprinkler design have paralleled those made in mechanical move systems. As a result, manufacturers such as Lindsay Manufacturing Co. can provide computerdesigned sprinkler packages which are tailored to match water application to the specific texture, infiltration rate and holding capacity of the soil. Table 2. Fertilization of Various Turfgrass Species Turfgrass Species Bentgrass, colonial Bentgrass, creeping Bermudagrass, common Bermudagrass, hybrid Nitrogen (lb/1000 sq. ft/month) (spring-summer) Turfgrass Species Kentucky bluegrass Kikuyugrass Ryegrass, annual (for overseeding) Ryegrass, perennial Nitrogen (lb/1000 sq. ft/month) 0.5 (Sept-May) Dichondra 1 St. Augustinegrass 0.5 Fescue, fine Zoysiagrass Fescue, tall 0.5 Source: Turfgrass Integrated Weed Management, University of California Statewide Integrated Pest Management Project,

6 Figure 3. Maximizing Harvestable Area In many cases, center pivot and lateral move systems can be designed so that turf can be harvested in the wheel track. This is done by using a combination of tires which have minimum ground pressure and sprinklers which are directional and/or placed on booms behind the wheel. Center pivot systems have the lowest labor requirement compared with other irrigation systems. They are available in fixed (mounted to a concrete pad) or mobile versions which can be towed from field to field. Center pivots allow turf production on hilly terrain (slopes up to 15%) and provide precision control options including automatic and remote operation. As a result, they have become a fast-growing form of turf irrigation. Sprinklers can be mounted on top of the spans or on drop-tubes to reduce water loss from drift and evaporation. Available with a choice of drive-motor speeds, center pivots provide the flexibility of using frequent, light watering or more soaking irrigation as turf matures. The addition of a corner arm to the center pivot can provide up to 22 acres (8.9 ha) of additional irrigated coverage. The corner arm can also be used to bring unused areas caused by irregular boundaries or obstacles into production. The shape of the field and the potential for additional production acres are generally the determining factors when considering the investment of the corner system. Lateral move irrigation systems can provide maximum coverage (up to 98%) on rectangular fields up to a mile and a half long. This coverage advantage balances a higher capital investment and is making them a frequent choice on high value crops Figure 4. Efficient Small-Field Irrigation Mini-laterals (shown above) and mini-pivots provide an efficient method for irrigating turf fields under 60 acres (24 ha). such as turf. Water can be supplied from a ditch, making them ideal for conversion from flood irrigation, or from a hose. In addition, hose-fed systems can be pivoted or towed for use on adjacent fields. Annual operating costs for lateral systems are generally more than center pivot systems and less than guns. Traveling guns use a large capacity nozzle and high pressure to throw water out over the turf as it is pulled through an alleyway in the field. Guns require a higher operating pressure and are more expensive to operate, especially in the cost of labor. A traveling gun system may take up to one week for a complete run. Additionally, gun systems do not provide as uniform a watering pattern as mechanical move systems.

7 Figure 5. Minimizing Labor/Energy Cost Remote programming and control of center pivots is becoming a major factor in reducing labor costs and utilizing least-cost power. Turf growers can also automatically change application to match varying soil types and control application of chemicals and fertilizer. IRRIGATION SYSTEM INVESTMENT COMPARISONS Lindsay Manufacturing Co. has developed a wide range of irrigation application equipment to meet the needs of turf growers who know the benefits of irrigation. Each system is designed for maximum efficiency to save time and labor, while reducing turf production risks and promoting a quality and marketable product. The center pivot was the most efficient irrigation system in the study and the big gun was the least efficient in terms of total operating and ownership costs. The center pivot, pivot with corner attachment and lateral move (for rectangular fields) provides the most costefficient and economical systems for irrigating. ADDITIONAL EQUIPMENT NEEDED FOR IRRIGATION MANAGEMENT Soil probes are used to measure the depth the soil is dry or wet in order to understand the effectiveness of current irrigation schedules. Tensiometers are soil moisture sensing devices that measure the suction created by drying soil. They are effective tools to measure drying and wetting until the soil gets too dry. The data from these instruments can be used to determine irrigation scheduling. Gypsum blocks and granular matrix sensors measure electrical resistance. The choice of equipment to use to measure the need for irrigation varies with soil types and vary in cost among suppliers. Sensor manufacturers supply instructions on how to install and read their particular pieces of equipment. Table 3. Comparative Cost of Sprinkler Systems (square 160 acres [64.8 ha], 100 foot [30.5 m] deep well in middle of property). Center Pivot Pivot with Corner Lateral Move Big Gun Number of Systems Required (160 acres, 64.8 ha) Annual Ownership Costs/Acre $57.81 $66.71 $69.91 $56.91 Capital Costs/Acre $ $ $ $ Operating and Ownership Cost $91.78 $ $ $ Source: "Selecting a Sprinkler Irrigation System," North Dakota State University, Extension Service, Bulletin AE0-91, Revised,

8 SUMMARY The public demands instant beautification of their lawns, golf courses and other public areas through the placement of sod that is thick, green and appealing. Irrigation management is the critical practice that ensures that turfgrass is the quality expected. Mechanical move irrigation systems place the water where it is needed and when it is needed. Additional benefits of irrigation: Where soil salinity is a problem, irrigation can help leach the salt from the soil. Improved pest control is possible under irrigation. Healthy turf can out-compete weeds and reduce the chances of their becoming established. The number of herbicide applications may be able to be reduced. Also, healthy turfgrass is less prone to attack by insects, diseases, and weeds. Irrigation can shorten the time from seeding to harvest. For example, zoysiagrass is normally considered a two-year crop, but with sprigs set in July and irrigation systems in place to push the growth of the grass, harvest may be moved to August of the following season. Accelerating production cycles saves money and increases profit opportunities. References: Brown, Paul W., Basics of Evaporation and Evapotranspiration, Turf Irrigation Management Series: I, University of Arizona. Carrow, Robert N., Robert C. Shearman, James R. Watson, Turfgrass, ASA-CSSA-SSSA, Cook, Tom, et. al., Common Turfgrasses in the Pacific Northwest, WSU Turfgrass Science, Oregon State University, Department of Horticulture, Duble, Richard L., Water Management on Turfgrasses, University of Texas, Agricultural Extension Service. Eisenhauer, Dean E., Paul E. Fischback, Water Measurement Calculations, University of Nebraska, Cooperative Extension Service, Harms, Rebecca, et. al., Kentucky Bluegrass Seed Production Management in Western Nebraska and Eastern Wyoming, University of Nebraska Cooperative Extension, NF98-377, Klocke, Norman L., et. al., Evapotranspiration (ET) or Crop Water Use, University of Nebraska, Cooperative Extension Service, G A, Klocke, Norman L., et. al., Water Management for Irrigation in Nebraska, University of Nebraska, Cooperative Extension Service, Landry, Gil, Turfgrass Water Management, Leaflet 399, The University of Georgia College of Agricultural and Environmental Sciences, McCarty, L. B., Sod Production in Florida, University of Florida, Cooperative Extension Service, Ossa, John, et. al., The ET Connection, The Irrigation Association, Scherer, Tom, Selecting a Sprinkler Irrigation System, North Dakota State University, Extension Service, Bulletin AE0-91, Revised, Thompson, Steven J., et. al., Using Soil Moisture Sensors for making Irrigation Management Decisions in Virginia, Virginia Cooperative Extension, Publication Number , Wright, James L., Derivation of Alfalfa and Grass Reference Evapotranspiration, in proceeds of International Conference, Irrigation Association, San Antonio, TX, November 3 6, Yonts, C. Dean, Norman L. Klocke, Irrigation Scheduling Using Crop Water Use Data, University of Nebraska, G A, For more information, see your local dealer. Lindsay Manufacturing Co. P.O. Box 156 Lindsay, NE USA Phone: (402) FAX: (402) LMC