Benefits and misconceptions of turf and water conservation
Well maintained turf provides many functional, recreational, and ornamental benefits, which are summarized in Table 1.
Table 1. Benefits of turf.
|Dust and mud control
|Entrapment of pollutants
||Low cost surfaces
||Soil loss control
||Safe playing surfaces
|Adapted from J.B. Beard and R.L. Green, 1994, from The Journal of Environmental Quality, The Role of Turfgrasses in
Environmental Protection and Their Benefits to Humans.
The key to water conservation is education. Plants such as turfgrass are not inherently wasteful, but improper plant maintenance practices can lead to inefficient use of water. For example, research has shown that residential irrigation systems with automatic timers use 47% more water than systems without timers. Numerous misconceptions exist regarding turf areas as high water-users compared to other landscape plantings, which have no scientific basis. In studies that are available, which compare water use or evapotranspiration (ET), trees and shrubs are regularly found to be higher water users than turfgrass. For instance, one study found that an average, mature oak tree will require an amount of irrigation equivalent to 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.
Another misconception is that native plants should be selected over turfgrass species in the landscape to conserve water. This is seldom viable because many turfgrass varieties have been developed that have low water use rates and thereby have improved drought resistance. Visit the National Turfgrass Evaluation Program web site (http://www.ntep.org) for information on selecting turfgrass with superior drought resistance. Selecting native plants over turfgrass species does not necessarily result in low water use or minimal maintenance.
Turfgrass water conservation checklists
Water conservation can be achieved by incorporating several strategies into the turfgrass landscape. These strategies involve reducing ET loss while promoting deep rooting to maximize drought resistance, and eliminating waste by improving the efficiency of irrigation.
Checklist for cultural management practices
- Follow the one-third rule when scheduling mowing events – Regular and frequent mowing helps to minimize leaf area and turfgrass ET.
- 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. Higher HOC also increases leaf area and ET losses. For irrigated turf, a lower HOC in summer may reduce ET without significantly reducing rooting depth. Further research is needed, however, before the traditional “raise the HOC in summer” recommendation is abandoned.
- Apply fertilizer nitrogen at minimal levels timed to specific needs of turfgrass – Nitrogen (N) promotes leaf area (and ET) and reduces rooting depth, thus increasing the need to irrigate. Nitrogen, especially water soluble N, must be kept to its lowest possible level needed to sustain turf function.
- Potassium must be applied in balance with N – 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 inadequate, then K should be applied at levels that are approximately 50% to 75% of the total annual N.
- 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. Any factor(s) that inhibit rooting can increase the need to water. Such factors include acidic soil pH (< 5.5), excess thatch (> 0.3”), soil compaction, over-watering, excessively close mowing, excess N fertilization, and high soil temperature. Two or more of these 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.
- Select turfgrasses that have scientifically documented low water requirements – Turfgrass species and varieties 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. Low water use does not necessarily mean superior drought resistance because rooting depth is also an important drought resistance component.
- Eliminate competition for plant available soil water – Remove all weeds that compete with turfgrass for limited plant available water. Design landscape plantings to minimize adverse interactions with turf areas.
Figure 1. Mean monthly precipitation and temperature for Massachusetts (30-year averages).
For example, mean water use (ET) rate during July and August for Kentucky bluegrass is approximately 5.6 inches per growing month, which is well above that provided by natural rainfall events. Supplemental irrigation is typically needed during this period to meet water use requirements and maintain turf appearance and function.
Checklist for irrigation practices and design
- Plan irrigation scheduling based on ET – Calculate irrigation amounts based on water lost as ET. This prevents over-watering (leaching losses) and under-watering (shallow rooting) of turf. Kentucky bluegrass will lose approximately 1.4” per week on average as ET during the irrigation season (July and August, see Figure 1). Irrigation systems can be fitted with ET signaling controllers. Additional water savings of 20% are possible, as research has shown that acceptable turf quality can be maintained by replacing just 80% of that lost as ET.
- Know your 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 soil infiltration rates, which promote surface water runoff. Surface water runoff occurs when irrigation rates exceed soil infiltration rates. Multiple cycling of irrigation is required to prevent runoff, which is wasteful and can move fertilizers and pesticides into surface water. Irrigation systems can be fitted with features that permit multiple cycling so that irrigation (ET replacement) amounts are applied using short, repeated cycles to minimize runoff.
- Eliminate waste – Irrigation systems that include rain sensing override devices can eliminate unnecessary irrigation during rainfall events. Turf areas irrigated on narrow strips are difficult to water efficiently without promoting wetting of non-grassy areas, and therefore should be avoided. Irrigating during calm periods such as early morning can promote more uniform distribution of water and reduce evaporative losses. Clean-up sidewalks and paved areas following maintenance operations by sweeping rather than by spraying with a hose. Adjust systems to minimize irrigation that reaches impervious surfaces and repair all leaks as soon as detected.
- 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 with increasing soil temperature. Inspect for proper soil wetting depth and rooting potential by soil sampling. Allow for mild drought stress (leaf roll/fold, foot printing) to occur between irrigation events to promote deeper rooting and drought resistance. Maintaining root zones at field capacity by over-watering will inhibit rooting (and decrease drought resistance) and promote disease and soil compaction.
- Identify “hot spots” – Turf areas prone to drought stress are most often caused by a lack of uniform water coverage from clogged, blocked, and sunken irrigation heads. As distribution uniformity decreases, the amount of irrigation water that must be applied to maintain uniform growth increases. The solution is prompt repair of the irrigation system. Qualified irrigation specialists should check irrigation systems for distribution uniformity at least once a year.
By implementing water conservation techniques as outlined, research has shown that water savings of more than 50% on average can be achieved. As stated previously, it is not the grass plants that are the source of problems related to water usage, but rather it is improperly maintained turf areas along with poorly designed and operated irrigation systems. In the end, proper communication and research-based education is essential for conserving our water resources and protecting the environment.
For more information
Commonwealth of Massachusetts water regulations, water quality, and associated information can be accessed through the Massachusetts Department of Environmental Protection:
1 Winter Street
Boston, MA 02108