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Irrigation and Water Management

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objective

Reduce water use for turf management to the lowest possible level, to conserve and protect our most precious natural resource.

Implement water conservation strategies for both economic and judicious reasons.

  • The demand for potable water (drinking water) for agricultural, residential, and industrial use is expected to increase in the future while our supply of water will remain essentially unchanged.
  • When rainfall is insufficient and water resources become limited, supplemental irrigation required to sustain plantings such as lawn and landscape turf is often among the first uses to be placed on water use restrictions, in order to conserve water for higher priority uses such as drinking and hygiene.
  • Increasing demand along with controlled supplies serve to drive up water-related costs.
  • Be sure to always fully comply with local and state water use regulations and restrictions.

Reconsider the replacement of turf areas with tree and shrub plantings.

  • The use of trees, shrubs and other ornamental plantings in the landscape in lieu of turf does not necessarily suggest low water use or minimal maintenance.
  • In studies that are available, which compare water use or evapotranspiration (ET), trees and shrubs have regularly been found to be higher water users than turf.

Example: Research has demonstrated that, on average, one mature oak tree has water requirements equivalent to approximately 1800 ft2 of turf. This in large part is due to the greater leaf canopy surface area that is exposed to atmospheric (evaporative) demand.

  • Additionally, adjacent trees and shrubs in the landscape commonly benefit from irrigation applied to turf.

Be familiar with the concept of evapotranspiration (ET).

  • Evapotranspiration is the sum total of water lost to the atmosphere due to evaporation from the soil surface plus transpirational water loss (water that is absorbed by pant roots, travels through plants, and is lost to the atmosphere via plant leaf surfaces).
  • In high quality turf where 95% of the soil surface may be shaded by leafy vegetation, the major contributor to ET is transpiration.
  • ET increases with increasing solar radiation, high temperatures, wind, and decreasing relative humidity.

Select turfgrass species and cultivars with demonstrated water use efficiency when possible and appropriate.

  • A number of modern turfgrass varieties have been developed to provide acceptable function and quality with reduced water input.
  • By selecting turfgrass species (and cultivars) that have scientifically documented low water requirements or superior drought resistance, the turfgrass manager can delay or postpone drought stress injury and associated declines in turfgrass quality and function during extended periods of little or no water.
  • Turfgrass species and cultivars with low leaf area (slow growth rates, narrow leaf width), high leaf and shoot densities, and horizontal leaf orientation use less water. Kentucky bluegrass varieties can vary by as much as 30% in their ET rate due to these plant (morphological) factors.
  • Bear in mind that low water use does not necessarily equate to superior drought resistance because rooting depth is also an important drought resistance component. 

objective

Carry out management practices with responsible water use as a priority.

Minimize supplemental irrigation to the lowest level required for turf function and quality.

  • Irrigation should be initiated at the onset of mild drought stress to recharge the root zone unless dormancy is permissible within the management program.
  • Irrigation should be scheduled in order to minimize the duration of leaf wetness, so as to reduce the incidence of diseases.
  • Maintain and adjust irrigation systems according to weather conditions.
  • Incorporate hand watering into the management program when appropriate.
  • Always supply adequate water for establishment, renovation, repairs, and overseeding.

Follow the '13  Rule' when scheduling mowing events.

  • Regular and frequent mowing helps to minimize water loss by minimizing leaf area, and in turn, turf ET.
Figure 7. Irrigate judiciously to promote optimum turf health and protect water resources.

Maintain sharp mower blades.

  • Dull mower blade injury can increase water use by delaying the healing of open wounds following mowing events. These wounds also promote disease infection.

Raise the height of cut (HOC) as summer progresses. *

  • Higher mowing heights promote deeper rooting and therefore access to greater amounts of soil water. This is especially true in spring when 60% of the total annual root mass is produced, and especially beneficial for un-irrigated turf areas that can experience extensive root dieback during the summer stress period.
  • * Keep in mind that higher HOC can increase leaf area and hence ET losses during hot and dry conditions. High maintenance, irrigated turf areas may be able to withstand a lower HOC in summer than non-irrigated turf areas. A lower HOC results in lower leaf area and reduced water loss to ET, thereby promoting water conservation in such situations.

Apply fertilizer nitrogen at minimal levels timed to the specific needs of the turf.

  • Excess nitrogen (N) promotes increased leaf area (and thus ET) and reduces rooting depth, thereby increasing water loss and the need to irrigate.
  • Nitrogen, especially water soluble N, must be kept to the lowest possible level needed to sustain the desired level of turf performance.
  • Excess N, and also phosphorus (P), can move out of turf systems with leaching and runoff and negatively impact water quality.

Apply potassium in balance with nitrogen.

  • Potassium (K) is a nutrient that is important to turf during stress periods.
  • Soil testing is needed to identify K deficiencies. If soil K levels are adequate based on a soil test, then K should be applied at levels that are approximately 50% to 75% of the total annual N.

Apply herbicides intelligently.

  • Herbicides should be applied only as needed and according to label directions.
  • Pre-emergence herbicides have a greater impact on roots than on shoots. Hence, turfgrass shoots may be unaffected while root activity is significantly reduced.
  • Use split applications of soil-applied pre-emergence herbicides when appropriate to reduce the potential for adverse effects on turfgrass roots.
  • Spot treat for broadleaf weeds, when possible, to limit stress; avoid blanket applications of all herbicides when air temperatures exceed 85º F.

Alleviate root-related stresses.

  • Research has shown that deep rooting may play a more important role in water conservation and drought resistance than low ET.
  • Factors that inhibit rooting can increase the need to water.
  • Factors that inhibit rooting include acidic soil pH (< 5.5), excess thatch (greater than 1/2 inch), inadequate depth of soil for the root zone, soil compaction, over-watering, excessively close mowing, excess N fertilization, and high soil temperatures.
  • Two or more root-inhibiting factors in combination can significantly reduce rooting depth more than any single factor when considered alone.
  • Compaction and thatch are especially problematic because these conditions also promote runoff, which reduces irrigation efficiency and increases the potential for environmental compromise.

Monitor and manage thatch accumulation.

  • Manage thatch effectively. When levels exceed 1/3 to 1/2 inch, consider corrective action to promote deeper rooting into the soil and to limit rooting that is confined to the poor nutrient and water holding environment of the thatch.

Eliminate competition for plant available soil water.

  • Remove all weeds that compete with turfgrasses for limited plant available water.
  • Design landscape plantings to minimize adverse interactions between ornamental plants and turf surfaces.

Plan irrigation scheduling based on replacement of evapotranspiration (ET) losses.

  • This prevents over-watering (which increases leaching and runoff losses) and under-watering (which encourages shallow rooting) of turf.

Example: On average, a Kentucky bluegrass turf will lose approximately 1.4 inches of water per week as ET during the irrigation season (July and August).

  • Irrigation systems can be fitted with ET signaling controllers.
  • Additional water savings of up to 20% are possible using deficit irrigation techniques.  Research has shown that acceptable turf quality can be maintained by replacing less than 100% of water lost as ET.  Achievable savings may vary based on factors such as management level, use of the turf, turfgrass species and cultivars present, soil type, time of year, prevailing weather conditions, etc.

Figure 8. Inches of irrigation water required to wet soil to a predetermined depth chart. Know the impact of soil type.

  • Sands hold approximately half as much plant available water as loam soils and soils high in clay, and therefore sands must be irrigated more often.
  • Compacted soils and soils high in clay exhibit low water infiltration rates, which promotes surface water runoff.
  • Heavier soils (loams, clays) and soils with a high percentage of organic matter will retain water for a longer period than sandier soils.

Example: Using the adjacent chart (click to enlarge), one inch of water (indicated by the dashed line) applied to a clay soil would wet the soil to field capacity to a depth of approximately 5 inches; a loam to a depth of approximately 7 inches; and a sand to a depth of approximately 15 inches. Equivalently, to wet a soil to a depth of 12 inches (indicated by the dotted line) 0.75 inches of water is needed for sands; 1.5 inches of water for loams; and 2.5 inches of water for clays. Hence, it takes more than 3 times as much water to recharge a clay soil to field capacity to a 12-inch depth compared to sands as a result of the greater soil moisture-holding capacity associated with fine textured soils.

Figure 9. Use multiple short irrigation cycles to increase water infiltration, to prevent runoff, to promote efficient use of irrigation water, and to avoid the problems shown here: wetting of non-grassy areas and hard surfaces, and waste of precious water resources. Eliminate waste.

  • Narrow strips are difficult to water efficiently without promoting wetting of non-grassy areas, and therefore should be avoided, or should have irrigation systems designed to apply water without waste.
  • Adjust systems to minimize irrigation that reaches impervious surfaces and repair all leaks as soon as detected.
  • Correct areas of poor drainage to reduce pooling and ponding of water.
  • Clean up sidewalks and paved areas following maintenance operations by sweeping rather than by spraying with a hose.
  • Irrigation systems that include rain sensing override devices can eliminate unnecessary irrigation during rainfall events.
  • Irrigating during calm periods such as early morning can promote more uniform distribution of water and reduce evaporative and off-target losses that can be significant during the heat of the day or during breezy conditions.

Water deeply and infrequently.

  • Water to fully recharge the plant available soil moisture pool and to insure that soil is wet to the maximum rooting depth. This is best achieved by irrigating according to ET.
  • Rooting depth declines as summer progresses and soil temperatures increase. Inspect for proper soil wetting depth and rooting potential by soil sampling... a soil probe is an excellent tool for this purpose.
  • Allow for mild drought stress (leaf roll/fold, foot printing) to occur between irrigation events to promote deeper rooting, drought resistance, and greater overall turf resiliency.
  • Maintaining root zones at field capacity by over-watering will inhibit rooting, decrease drought resistance, and promote disease and soil compaction.

Maximize the amount of water that enters the root zone.

  • Address conditions that reduce soil infiltration rates such as soil compaction, thatch, and hydrophobic soils.
  • Under conditions associated with low infiltration the necessary amount of water should be applied using several short cycles or multiple irrigation events (referred to as multiple cycling), rather than applying all the water in one event.
  • Multiple cycling increases water infiltration, reduces runoff, prevents erosion, and minimizes waste. Multiple cycling can be done manually, or irrigation systems can be fitted with features that make the process automatic.
  • Irrigation should be scheduled and applied when wind conditions are minimal whenever possible in order to achieve a more uniform application.

objective

Manage for drought dormancy when the management program and user expectations allow.

Figure 10. Limit foot and vehicle traffic on drought-stressed and dormant turf to avoid the potential for injury. The damage to this heat and drought stressed turf is from a child’s toy, not an automobile. Understand that dormancy is a natural, adaptive response of turfgrasses to extremes of the growing environment.

  • When circumstances permit and with the right approach, dormancy of well-established and otherwise healthy turf can lead to substantial savings of time, labor and management resources.
  • Drought dormancy, however, is commonly not compatible with higher expectation levels in terms of appearance (higher-end lawns) and function (golf courses, premier athletic fields).
  • This leaves the turf manager with two basic choices: to manage for dormancy or to provide to supplemental irrigation.

Acknowledge that dormancy should be an 'all or nothing' commitment.

  • It is important to avoid irrigation entirely unless adequate and consistent evapotranspiration (ET) replacement can be achieved.
  • Irregular and insufficient irrigation during stress periods can actually further deplete valuable carbohydrate reserves and negatively impact later recovery.
  • If dormancy persists for an extended period (perhaps 30-60+ days depending on species, soil type, etc.), however, reduced recovery can be expected.

Restrict traffic on dormant turf to the lowest possible level.

  • The turfgrass shoots that die back when dormancy progresses are not able to adequately cushion and protect the critical plant structures that will ultimately facilitate re-growth and recovery.

Mow only when absolutely necessary.

  • If a mowing event is needed (according to the 1/3 Rule), avoid mowing during the hottest part of the day (this benefits the turf as well as the mower operator).

Monitor carefully for pest problems.

  • Chinch bugs and weed encroachment are particular problems for dormant lawns.
  • Pest damage will not be readily apparent during dormancy and affected areas may not recover when moisture returns.
  • If control is warranted, rely on spot treatments when possible instead of blanket applications to reduce undue stress on the turf.

Do not fertilize dormant turf.

  • Turfgrass plants need to be actively growing in order to absorb and make use of nutrients.
  • Fertilizer applied to dormant turf is much less likely to benefit the plants and much more likely to be lost from the system, increasing the potential for environmental impact.

Recognize that even under favorable circumstances, extended dormancy may not result in 100% recovery when conditions moderate.

  • It is prudent to allow turf to enter dormancy with reasonable expectations and plan ahead for the possibility of overseeding or targeted fertilization later in the season to achieve acceptable recovery.

objective

Ensure that irrigation systems are properly designed, installed, and maintained.

Note: The following irrigation system BMPs are adapted with permission from BMPs for Turf and Landscape published by the Irrigation Association (IA).

Assure overall quality of the irrigation system.

  • The purpose of an irrigation system is to provide supplemental water when rainfall is not sufficient to maintain the turf and landscape for its intended purpose.
  • Sound water delivery and management practices are necessary to distribute water to adequately maintain plant health while protecting water resources and the environment.
  • Assuring the overall quality of the system requires attention to system design, installation, maintenance and management.

Guidelines for irrigation system design, installation and management:

  • The irrigation system should be designed to be efficient and to uniformly distribute water.
  • The irrigation system should be installed according to the design specifications.
  • The irrigation system should be regularly maintained to preserve the integrity of the design and to sustain efficient operation.
  • The irrigation schedule should be managed to maintain a healthy and functional landscape with the minimum required amount of water.

Design the irrigation system for the effective, efficient and uniform distribution of water.

  • Test water for irrigation suitability. Water department or board of health test results can often be accessed for this information.
  • To conserve and protect water resources, the irrigation designer should select appropriate equipment components that meet state and local code requirements and site requirements.
  • Specific criteria that should be considered in the design include soil type, slope, root depth, plant materials, microclimates, weather conditions and water source (e.g., quantity, quality and pressure).

Install the irrigation system to meet the design criteria.

  • To conserve and protect water resources, the installed components shall meet the irrigation design specifications, manufacturer's specifications, and state and local code requirements.
  • The installation should result in an efficient and uniform distribution of water.
  • The irrigation contractor or installer shall be licensed and/or certified where applicable, and insured.

Maintain the irrigation system for optimum performance.

  • The irrigation system should be regularly serviced to maintain the performance of the system as designed.
  • To conserve and protect water resources and the environment, the serviced components should meet the irrigation design specifications, manufacturers specifications, and state and local code requirements.
  • The maintenance should result in sustaining an efficient and uniform distribution of water.
  • The maintenance contractor, owner, manager, or irrigation contractor shall be licensed and/or certified where applicable, and insured.

Manage the irrigation system to respond to the changing requirement for water in the landscape.

  • To conserve and protect water resources and the environment, the irrigation schedule shall be changed as required to provide supplemental water to maintain a functional, healthy turf and landscape with the minimum required amount of water.