The culture of creeping bentgrass (Agrostis palustris Huds.) at low mowing heights on putting greens in the hot humid region of the USA presents numerous water management problems. Frequent irrigation of greens to prevent water stress has been credited with producing shallow rooted turf with reduced tolerance to environmental stress. The present study was conducted to determine the relationship between irrigation frequency and turf quality, shoot density, and root length density for five cultivars of creeping bentgrass grown on a sand‐based root zone and maintained to putting green standards. A total of 81 plots, 1.5 by 1.5 m each, were established on a USGA‐type root zone mixture and organized into nine irrigation cells of nine plots each. Each irrigation cell could be irrigated individually. One plot in each irrigation cell was planted to the following bentgrass cultivars: A‐4, Crenshaw, Mariner, L‐93, and Penncross. The remaining four plots in each irrigation cell were also planted with bentgrass but were not a part of this study. Irrigation frequency treatments of 1‐, 2‐, and 4‐d were imposed on three irrigation cells each. After establishment, measurements of turf quality, shoot density and root length density were made over a 2‐yr period. In both years, Crenshaw and L‐93 had the best turf quality. At the end of the study, shoot densities for Crenshaw, L‐93, and A‐4 were 37 to 42% greater than Mariner and Penncross. Because of frequent rainfall events in 1997, there were no significant (P ≤ 0.05) effects of irrigation frequency on shoot density or root length density. However, in 1998, turf was more dependent on irrigation and bentgrass irrigated every 4 d had significantly greater turf quality, shoot density, and root length density than that watered every 1 or 2 d. The data show that even under putting green management conditions, reduced irrigation frequency of bentgrass produces a larger and deeper root system resulting in greater overall plant health, turf quality, and shoot density.

ation (Huang et al., 1998) decrease root growth and increase root mortality. In addition, a synergistic effect The culture of creeping bentgrass (Agrostis palustris Huds.) at between high soil temperature and low soil aeration furlow mowing heights on putting greens in the hot humid region of the USA presents numerous water management problems. Frequent ther contributes to bentgrass decline (Huang et al., 1998).irrigation of greens to prevent water stress has been credited with Very short mowing heights also reduce root growth of producing shallow rooted turf with reduced tolerance to environmen-

Proper water management is a major responsibility of managers of creeping bentgrass grown on putting greens in the hot and humid southern states. The combination of shallow root systems, sand-based root zones, high temperatures, and high evaporative demands frequently results in severe drought stress on bentgrass (Agrostis palustris Huds.) greens. This study was initiated to determine the effects of irrigation frequency on creeping bentgrass turgor pressure and on the O2 and CO2 concentrations in a sand-based root zone mixture. In total, 81 plots, 1.5 × 1.5 m each, were established on a USGA-type root zone mixture and organized into 9 groups of 9 plots each. Each group could be irrigated individually. One plot in each group was planted to either `A-4', `Crenshaw', `Mariner', `L-93', or `Penncross' creeping bentgrass. Irrigation frequency treatments of 1-, 2-, and 4-day replacement of historical PET were imposed on three groups each. After establishment, measurements of the leaf water potential, osmotic potential, soil oxygen concentration, and soil carbon dioxide concentrations were made over a 1- to 2-year period. Bentgrass irrigated every 1 or 2 days had significantly (P = 0.05) greater turgor pressures at 0600 hr as compared to turf irrigated every 4 days in 1997. No differences were seen in 1998 due to drier environmental conditions. Concentrations of O2 and CO2 in the soil air remained in the optimal range for all treatments, indicating that lack of O2 in the root zone as a result of frequent irrigation may not be the primary cause for reduced rooting depth of bentgrass grown on highly permeable sand-based root zone mixtures.