A key aspect in the establishment of turfgrass sod is rapid rooting or “knitting” of the sod into the underlying soil. Factors that ensure rapid sod rooting include 1) proper soil aeration; 2) adequate moisture in the underlying soil; and 3) transplanting techniques that minimize desiccation (Beard, 1973). Rapid root extension into the soil is essential to gain access to water and nutrients to support the establishment of the sod plants. Therefore, understanding the impact of various management options, including irrigation, is crucial to maximize success in sod establishment.
Irrigation management options include both the frequency and amount of irrigation. Beard (1973) recommended irrigating newly laid sod lightly on a daily basis to maintain adequate moisture level in the sod with thick-cut sod requiring less frequent irrigation than thin sod; however, research is lacking that examines the direct relationship between sod root establishment and irrigation frequency or volume. There are alternative speculations about the impact of irrigation on root extension in establishing sod. One hypothesis is that frequent irrigations with large amounts of water are needed to encourage rapid root growth, although there is the possibility that such intense irrigation could discourage deep rooting into the soil. A second hypothesis is that infrequent irrigations and/or deficit irrigations stimulate rapid root extension to reach layers deep in the soil that might contain stored water. Although deficit irrigation during establishment could be beneficial in terms of water conservation, it may also negatively impact shoot growth and sod establishment.
Surprisingly, virtually no information appears to have been obtained on root extension of turfgrasses during turf sod establishment. Studies on temporal changes in root populations of established sod subject to various irrigation regimes may offer some guidance about root response to various irrigation regimes during establishment. In a study of established sod of five warm-season grasses, Doss et al. (1960) found that rooting depth was decreased for all species as the amount of water applied was increased. Qian and Fry (1996) examined the effect on water extraction by zoysiagrass (Zoysia japonica Steud.) only after sod had grown for 107 d in 92-cm deep cylinders. Two irrigation regimes (daily and at leaf rolling) were then applied to this established sod. Infrequent irrigation resulted in greater water extraction and presumably as a result of additional root growth at 55- and 75-cm depths as compared with daily irrigation. The root mass of zoysiagrass was found to be positively associated with drought survival (Marcum et al., 1995). Rooting of tall fescue (Festuca arundinacea) by established sod in response to differing amounts of water application (20%, 60%, and 100% evapotranspiration) applied twice weekly was viewed directly with mini-rhizotrons (Fu et al., 2007). Deficit irrigation tended to result in greater numbers of roots at the end of the growing season (August and September) than in plots watered to replenish 100% evapotranspiration. Fu and Dernoeden (2009) also used mini-rhizotrons to document that infrequent irrigation of creeping bentgrass (Agrosis stolonifera L.) resulted in more roots and greater root lengths than the treatment of daily irrigation. Overall, these studies with established sods indicate that rooting depth is stimulated by limiting the frequency or amount of water application.
A critical unresolved issue is the impact of restricted irrigation on root extension during the critical time of sod establishment. The objective of this work was to provide information on root extension of four warm-season grasses during sod establishment. Root extension was observed by sod establishing on soil columns in clear acrylic tubes. Based on studies of previous investigations with established sods, the hypothesis to be resolved is that water deficit either by infrequent irrigation intervals or amount of irrigation results in increased root growth.
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Bastug, R. & Buyuktas, D. 2003 The effects of different irrigation levels applied in golf courses on some quality characteristics of turfgrass Irrig. Sci. 22 87 93
Doss, B.D., Ashley, D.A. & Bennett, O.L. 1960 Effect of soil moisture regime on root distribution of warm season forage species Agron. J. 52 569 572
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Jordan, J.E., White, R.H., Vietor, D.M., Hale, T.C., Thomas, J.C. & Engelke, M.C. 2003 Effect of irrigation frequency on turf quality, shoot density, and root length denity of five bentgrass cultivars Crop Sci. 43 282 287
Madison J.H. Jr & Hagan, R.M. 1962 Extraction of soil moisture by ‘Merion’ bluegrass (Poa pratensis L. ‘Merion’) turf, as affected by irrigation frequency, mowing height and other cultural operations Agron. J. 54 157 160
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Wherley, B. 2011 Turfgrass growth, quality, and reflective heat load in response to deficit irrigation practices Evapotranspiration Leszek Labedzki Vienna, Austria In press