In the discipline of plant physiology, drought resistance is a broad term that encompasses mechanisms that enable plants to survive periods of dry weather and low amounts of precipitation. Drought tolerance and drought avoidance are two separate components of drought resistance.
Drought tolerance mechanisms include cellular osmotic adjustments to mitigate dehydration. Drought avoidance is the ability to maintain a plant’s water potential (i.e., maintain green, turgid, healthy tissues) during a period of high evaporative demand or a period of increasing soil water deficit.
Turfgrasses can exhibit drought avoidance capability by developing and maintaining a deep, extensive and viable root system, and possessing any physiological or morphological features that reduce evapotranspiration (ET) water losses. Previous research investigated water extraction patterns and root lengths for tall fescue (Schedonorus arundinaceus; formerly Festuca arundinacea) in a sandy loam root zone. As soil moisture in the top 8-inch (20-centimeter) root zone was depleted, soil moisture extraction actually increased from the 8-to-24-inch (20-to-60-centimeter) depth, even though only 10% of the roots were at that deeper depth. Thus, a small number of roots in the soil can contribute substantially to a plant’s ability to avoid drought. Similar results were observed with bermudagrass (Cynodon spp.)
Can tall fescue avoid the drama of drought stress by developing a deeper, more extensive root system and extracting water more effectively from a greater volume and depth of soil, while growing under drought conditions? Research was conducted at Colorado State University (Fort Collins) to understand how plant structure and function could influence drought-avoidance capabilities of tall fescue during drought stress, and compared to Kentucky bluegrass (Poa pratensis), also under drought stress.
This was a complex and replicated, multifactor two-year field study. Tall fescue (Rebel Jr. + Crewcut + Monarch) and Kentucky bluegrass (NuStar) sod was maintained on clay loam soil and mowed twice weekly at 2.5-inch (6.4-centimeter) height-of-cut. Drought stress was imposed in test plots by irrigating based on five deficit irrigation levels of 65%, 55%, 50%, 35% and 20% of ET in year one, and 75%, 70%, 60%, 45% and 30% of ET in year two. Turf plots were measured for visual quality, soil water content, root growth at three soil depths (0-12, 12-24 and 24-36 inches/0-30, 30-60 and 60-90 centimeters), number of days the turf remained green and viable, and canopy temperature.
The study results indicated tall fescue was better at avoiding drought, because tall fescue developed a deeper and more extensive root system compared to Kentucky bluegrass. Under deficit irrigation (i.e., imposed drought stress), tall fescue had 45% to 65% more root dry weight at the lower soil depths compared to Kentucky bluegrass. Tall fescue’s deeper roots were critical for survival because when soil moisture in the upper root zone was depleted, the tall fescue was able to access soil moisture lower in the root zone, continue transpiration and therefore maintain healthy turf growth and function, and maintain a lower canopy temperature as compared to Kentucky bluegrass as both species were maintained under drought stress.
Tall fescue has a bunch-type growth habit, and Kentucky bluegrass has a rhizomatous growth habit. Root architecture may have a role in the acquisition of soil moisture, but recent research is focusing on the rhizosphere and the interactions with the root zone’s biological environment and root function (https://gcmonline.com/course/environment/news/verdure-why-the-rhizosphere-matters).
Tall fescue can persist when water becomes limited. Therefore, in the northern and transition zone climates, turf-type tall fescue is gaining popularity for use in golf course roughs, bunker faces and low-input areas.
This research was guided by Tony Koski, Ph.D., (1957-2025). He was a dedicated family man, an outstanding educator and scientist, and a friend to so many in the turf industry. He wrote his own obituary and concluded with these poignant words: “May your lawns be green, your trees healthy, your friendships deep and never stop trying new things. In turf we trust.”
Source: Ervin, E.H., and A.J. Koski. 1998. Drought avoidance aspects and crop coefficients of Kentucky bluegrass and tall fescue turfs in the semiarid west. Crop Science 38:788-795.
Mike Fidanza, Ph.D., is a professor of plant and soil science in the Division of Science, Berks Campus, at Pennsylvania State University in Reading, Pa. He is a 25-year member of GCSAA.