Researchers have found that turfgrasses require water in amounts less than evapotranspiration (ET) to maintain acceptable visual quality (Feldhake et al., 1984; Fry and Butler, 1989; Fu et al., 2004; Qian and Engelke, 1999). Deficit irrigation is defined as supplying water in amounts less than actual ET measured under well-watered conditions and has become an increasingly popular conservation technique in turfgrass maintenance (Feldhake et al., 1984; Fry and Butler, 1989; Qian and Engelke, 1999). Irrigation deficits can be achieved by lengthening periods between irrigations or applying water more frequently at levels less than actual ET, which has been the approach of the aforementioned researchers.
Deficit irrigation in the transition zone of the United States is often practiced on tall fescue, a turfgrass that is popular in the transition zone of the United States as a result of its heat tolerance and ability to avoid drought with deep rooting. However, under well-watered conditions, tall fescue has a higher ET rate when compared with most cool-season turfgrasses (Fry and Huang, 2004). In an earlier Kansas study, we found that tall fescue watered twice weekly maintained acceptable quality between June and September at deficit irrigation levels of 40% or 60% ET, assuming the turf manager could tolerate a period of slight decline in quality (Fu et al., 2004). When deficit irrigation is practiced in most turf situations, soil is wetted to a shallower depth than traditional deep, infrequent irrigation. Periodically wetting the surface few centimeters of soil could influence growth and distribution of roots. Roots deeper in the soil profile, however, could be exposed to drying soil, which may influence their development. Despite the positive water-saving benefits of deficit irrigation, effects of this practice on tall fescue root development have not been well evaluated.
Soil drying, but not deficit irrigation, has been evaluated for its effects on turfgrass rooting. Bennett and Doss (1960) observed that rooting of cool- and warm-season forage grasses was enhanced by allowing the surface 60 cm of soil to dry to 15% versus 70% of available water content. During a dry down after irrigation treatments, soil under zoysiagrass (Zoysia japonica Steud.) watered at the onset of wilt had roots extracting water at depths greater than 50 cm, whereas soil under turf previously watered daily did not exhibit a similar drying pattern (Qian and Fry, 1996).
Measuring root changes in the field often results in error, because measurements are commonly taken by destructively sampling soil cores and determining the total roots present. The root-washing process can result in loss of a significant number of roots. The minirhizotron imaging technique allows root growth and development at a particular depth and location to be monitored in situ without destructive sampling (Huang and Liu, 2003; Upchurch and Ritchie, 1983). Murphy et al. (1994) demonstrated that determination of root length density using field cores and minirhizotron root counts was correlated (r2 = 0.86) in creeping bentgrass (Agrostis palustris Huds.) and annual bluegrass (Poa annua L.). The minirhizotron technique has also been used to effectively monitor creeping bentgrass root production, growth, and mortality under field conditions (Huang and Liu, 2003; Liu and Huang, 2002).
This is the third in a series of publications investigating turfgrass responses to deficit irrigation in the transition zone, the first reporting minimum deficit irrigation levels required to maintain turf quality (Fu et al., 2004) and the second investigating deficit irrigation effects on shoot growth and physiology (Fu et al., 2006). The objective of this experiment was to monitor rooting of field-grown tall fescue during deficit irrigation using the minirhizotron imaging technique.
Feldhake, C.M., Danielson, R.E. & Butler, J.D. 1984 Turfgrass evapotranspiration. II. Responses to deficit irrigation Agron. J. 76 85 89
Fu, J., Fry, J. & Huang, B. 2002 Water savings and performance of four turfgrasses under deficit irrigation. Turfgrass Research. KSU Agr Exp. Stn. Rpt. of Prog. 892 1 5
Fu, J., Fry, J. & Huang, B. 2007 Growth and carbon metabolism of tall fescue and zoysiagrass as affected by deficit irrigation HortScience 42 378 381
Huang, B. & Fu, J. 2001 Growth and physiological responses of tall fescue to surface soil drying International Turfgrass Society Research Journal. 9 291 296
Murphy, J.A., Hendricks, M.G., Rieke, P.E., Smucher, A.J.M. & Branham, B.E. 1994 Turfgrass root system evaluation using the minirhizotron and video recording methods Agron. J. 86 247 250
Qian, Y.L. & Engelke, M.C. 1999 Turfgrass selection: Comparing three turfgrasses for minimum irrigation requirements, drought resistance and long-term performance Turfgrass Trends 8 4 8