(PHOTO COURTESY: SEED RESEARCH OF OREGON)
|
Turfgrasses provide many benefits to the environment including carbon dioxide sequestering, reduction of wind and water erosion,
and cooling of the environment. In spite of these documented benefits, there is increasing pressure to reduce the use of grasses
— primarily to reduce the water requirements of urban areas. In many settings, turfgrass is watered much more than is required
to maintain turf quality, often because of older irrigation systems or failure to understand how to water the grass. However,
there are choices that can be made in species and cultivars to reduce water usage.
In areas where they are adapted, warm-season grasses require less water than cool-season grasses. This is due to their different
leaf structure and method of carbon capture. Even within these species, however, it has been shown the improved seeded bermudagrasses,
such as Yukon and Princess 77, can use 25 percent less water than the hybrid bermudagrasses. If you're in an area that requires
green turf during the winter, the overseeded cool-season grasses can add to the water utilization of these species. In general
these species also do not do as well in shady sites.
In areas where cool-season species are utilized, selecting a water-saving grass may depend on whether you're looking for drought
avoidance, the ability to survive short periods without irrigation or the ability to perform with less water. In many areas
of the West, irrigation is required for survival. The dry summers, with low humidity, make for higher water-use rates. The
depth of the soil, the type, the slope and level of compaction all influence the availability of water to the turfgrass system.
As golf course superintendents study many trials looking at drought tolerance, they'll find some measure evapotranspiration
(ET) rates under non-limiting water conditions, which can be very different than ET rates with limited water. Other trials
just limit water availability. Some trials are outside while others are in greenhouses or controlled environments. The other
difficulty in evaluating trials is variation in species or cultivars in these trials making cross comparisons difficult. Kentucky bluegrass has the reputation of being a high water user. If you examine the trial performed at Kansas State by Bremer
et al in 2007 and to be repeated in 2009 (http://turf.lib.msu.edu/ressum/2007/8.pdf), the common Kentucky bluegrasses, which are the cheapest seed and are often used in consumer blends, used 22 inches of water
over the summer when irrigated at 50 percent wilt, while the Compact-America types and Mid-Atlantic-types of bluegrass had
excellent performance at 8 inches of water over the same period. So changes in the cultivars of Kentucky bluegrass could greatly
reduce the water requirements in even a hot environment for this species. These are measurements of the water required to
keep the turfgrass looking acceptable to the average homeowner using an end point they can understand.
Often, we read studies where it's decided to irrigate at a set percentage of evapotranspiration. These may be set to 100 percent,
80 percent, 60 percent and 40 percent of evapotranspiration. Ebdon et al (1998) examined the evapotranspiration, water loss
of different bluegrass cultivars in high (arid) and low (humid) evapotranspiration environments. Some cultivars had uniform
high or low water use in all environments while others varied depending on the environment. Again, in this trial, Mid-Atlantic
cultivars had low water use and the common types, such as Kenblue, had very high water use. In general, these types of trials
looking at water use are under well-watered conditions.
Richardson et al (2008) did dry-down cycles for extreme drought on Kentucky bluegrass. Again, America-types such as Mallard,
SR 2284, and Compact-type such as Diva and Midnight stayed green the longest. Although variation can occur, examination of
the NTEP (National Type Evaluation Program) drought trials or drought cycles in other trials can help find lower water-use
Kentucky bluegrasses.
Tall fescues are excellent drought avoiders because of their deep root system, as long as you have adequate, non-compacted
soil with good water-holding capacity. They are actually higher water users than most Kentucky bluegrasses, but they can stay
green all year long without supplemental irrigation in areas with summer rainfall or good soils.
Advances in tall fescues make them finer textured and denser than old cultivars, but most of them maintain good drought tolerance.
