Drought Tolerance of Tall Fescue and Bluegrass Cultivars
A desirable trait of cool-season lawn grasses, such as tall fescue (Festuca arundinacea) and Kentucky bluegrass (Poa pratensis), is that they stay relatively green throughout most of the year and do not go into complete winter dormancy like bermudagrass or zoysiagrass. The use of cool-season grasses for Arkansas lawns has been limited to northern regions of the state due to their poor heat and drought tolerance relative to warm-season grasses. In recent years, hybrid bluegrass cultivars, which are crosses between Kentucky bluegrass and Texas bluegrass (P. pratensis x P. arachnifera), have been released as a cool-season lawn turf option with improved heat and drought tolerance (Abraham et al., 2004). In addition, it has recently been demonstrated that there is variation in drought tolerance among cultivars within tall fescue (Karcher et al., 2008) and Kentucky bluegrass species (Richardson et al., 2008). Identifying cultivars of tall fescue, Kentucky bluegrass, and hybrid bluegrass with excellent drought tolerance may expand the use of cool-season turfgrasses for lawns in Arkansas. The objective of the following research was to determine the relative drought tolerance of various tall fescue, Kentucky bluegrass, and hybrid bluegrass cultivars.
Materials and Methods
This research was conducted at the University of Arkansas Research and Extension Center in Fayetteville, Ark. Forty-two cultivars of tall fescue, Kentucky bluegrass, or hybrid bluegrass (Table 1) were seeded into three replicate plots in the fall of 2006 on a native soil experimental area that was constructed under a rain-out shelter. The experimental area was maintained as a home lawn and was mowed weekly at a 2 inch height of cut. During the summer of 2007, drought stress was initiated by discontinuing irrigation and activating the rain-out shelter so that an automated, sliding roof would cover the plots, keeping them dry during rainfall events. Digital images were collected from each plot regularly during drought stress to evaluate green turf coverage over time and determine the drought tolerance characteristics of each cultivar. Non-linear regression (using a variable slope, Sigmoid curve) was performed on the digital image analysis data to predict Days50 values for each cultivar, which are the estimated number of days after irrigation was withheld until green turf coverage decreased to 50%.
Results and Discussion
The 42 cultivars tested in this trial are ranked from most to least drought tolerant in Table 1. The number of days after irrigation was withheld until green turf coverage dropped to 50% ranged from 52 d for 2nd Millennium tall fescue to 29 d for Solar Green hybrid bluegrass. This range of greater than three weeks (23 d) is significant when considering that a rainfall event would be probable during this period on a non-irrigated lawn in Arkansas. In such a case, cultivars in this trial that were most drought tolerant would be much more likely to retain acceptable green turf coverage between rainfall events compared to the more drought sensitive cultivars and not need supplemental irrigation. The only cultivar that was statistically as drought tolerant as 2nd Millennium was TB 390, an experimental hybrid bluegrass cultivar (Fig. 1). There were three cultivars with drought tolerance as poor as Solar Green: Champlain, A00-1400 Kentucky bluegrass, and TB 676 hybrid bluegrass; the latter two being experimental cultivars (Fig. 1).
In general, the tall fescue cultivars were more drought tolerant (higher Days50 values) than the bluegrasses. Ten of the eleven most drought tolerant cultivars were tall fescue whereas only one of the six least drought tolerant cultivars was tall fescue. All of the Kentucky bluegrass cultivars
were among the bottom half of those tested with regard to drought tolerance. There was not a clear trend in drought tolerance among hybrid bluegrass cultivars with two of the four (TB 390 and Thermal Blue) having Days50 values greater than 43, and the other two cultivars (TB 676 and Solar Green) having Days50 values below 33.
Previous research has shown that drought tolerance among tall fescue cultivars is primarily a function of high root/shoot ratio (Karcher et al.,
2008). However, root/shoot ratios were not evaluated in the present study. The mechanisms responsible for improved drought tolerance in
Kentucky bluegrass are less clear and do not appear to be related to root/shoot ratio (Richardson et al., 2008). Other factors, such as stomatal resistance, osmotic adjustment, reduced electrolyte leakage, and increased photosynthetic efficiency, probably play a greater role in the drought tolerance of Kentucky bluegrass compared to tall fescue. None of these factors were evaluated in the present study.
These results demonstrate that there are differences in drought tolerance among cool-season grasses used in Arkansas lawns. Therefore, drought tolerance screening should be performed routinely on these species so that cultivars may be selected that are best adapted for lawns where irrigation
in not available or is limited.
Abraham, E.M., B. Huang, S.A. Bonos, and W.A. Meyer. 2004. Evaluation of drought resistance for Texas bluegrass, Kentucky bluegrass, and their hybrids. Crop Sci. 44:1746-1753.
Karcher, D.E., M.D. Richardson, K. Hignight, and D. Rush. 2008. Drought tolerance of tall fescue varieties selected for high root:shoot ratios. Crop Sci. (in press).
Richardson, M.D, D.E. Karcher, K. Hignight, and D. Rush. 2008. Drought tolerance and rooting capacity of Kentucky bluegrass cultivars. Crop Sci. (in review).