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Ian R. Rodriguez and Grady L. Miller

Because high rates of nitrogen fertility are necessary for producing high-quality turfgrasses, quick, reliable methods of determining the N status of turfgrasses would be valuable management tools. The objective of this study was to evaluate the capacity of a hand-held chlorophyll meter (SPAD-502) to provide a relative index of chlorophyll concentrations, N concentrations, and visual quality in St. Augustinegrass [Stenotaphrum secondatum (Walt.) Kuntze]. Two experiments were conducted in a greenhouse in 1998 to evaluate the utility of SPAD readings. Established pots of `Floratam' were subjected to weekly foliar Fe treatments at Fe rates of 0 and 0.17 kg·ha–1 for 4 weeks. Six weekly nitrogen fertilizer treatments were applied in the form of ammonium sulfate at N rates of 0, 5.75, 11.5, 17.25, and 23 kg·ha–1 for 4 weeks. Greenhouse SPAD readings were not affected by Fe treatment, but N treatments resulted in differences in SPAD readings, visual quality, and chlorophyll concentrations. The readings were positively correlated with chlorophyll concentrations (r 2 = 0.79), visual ratings (r 2 = 0.74), and total Kjeldahl nitrogen (TKN) (r 2 = 0.71). Readings taken from field-grown `Floratam', `Floratine', and `Floralawn' St. Augustinegrass were poorly correlated (r 2 < 0.63) with chlorophyll concentrations and TKN. Unless future techniques improve dependability of the SPAD meter under field conditions for measuring chlorophyll and N concentration of a stand of turfgrass, the usefulness of such readings for the management of St. Augustinegrass seems limited.

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Ian R. Rodriguez, Grady L. Miller and L.B. McCarty

For drainage, turfgrass is often established on sand-based soils, which are typically nutrient-deficient and require supplemental fertilization. The objective of this study was to determine the optimum N-P-K fertilizer ratio for establishing bermudagrass from sprigs in sand. `FloraDwarf' and `Tifdwarf' bermudagrasses [Cynodon dactylon (L.) Pers. × C. transvaalensis Burt-Davy] were sprigged on a United States Golf Association (USGA) green [85 sand: 15 peat (v/v)] in Aug. 1996 at the Univ. of Florida's Envirogreen in Gainesville, Fla. `TifEagle' bermudagrass was sprigged on a USGA green [85 sand: 15 peat (v/v)] and `Tifway' bermudagrass [C. dactylon (L.) Pers.] was sprigged on native soil at Clemson Univ. in Clemson, S.C. in May 1999. Treatments consisted of fertilizer ratios of 1N-0P-0.8K, 1N-0P-1.7K, 1N-0.4P-0.8K, 1N-0.9P-0.8K, and 1N-1.3P-0.8K applied based on a N rate of 49 kg·ha-1/week for 7 weeks. Growth differences were apparent among cultivars. A 1N-0P-0.8K or 1N-0P-1.7K ratio is insufficient for optimum growth of bermudagrass during establishment, even when planted on a soil high in P. Increased coverage rate with additional P was optimized at a ratio of 1N-0.4P at all four sites. Increased coverage with P was greatest on the sand-based greens, probably due to the very low initial P levels of the soils. On two of the sand-based greens, P in excess of a 1N-0.4P ratio decreased coverage rate.

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Ian R. Rodriguez, Lambert B. McCarty, Joe E. Toler and Roy B. Dodd

Use of creeping bentgrass [Agrostis stoloniferous L. var. palustris (Huds.)] on golf greens has expanded into the hotter, more humid regions of the United States where its quality is often low during summer months. The summer decline in bentgrass quality may be partially attributed to respiration rates exceeding photosynthesis during periods of supraoptimal temperatures and adverse soil conditions, such as excessive CO2 and inadequate O2 levels. The objectives of this study were to examine the effects of high temperature, high soil CO2, and irrigation scheduling on creeping bentgrass growth. A growth chamber study was conducted using `A-1' creeping bentgrass. Treatments included all combinations of three day/night temperature regimes (26.5/21 °C, 29.5/24 °C, and 32/26.5 °C), three irrigation schedules (field capacity daily, field capacity every two d, and half field capacity daily), and four soil CO2 injection levels (10%, 5%, 0.03%, and a noinjection control). Creeping bentgrass shoot and root dry weights and net photosynthetic rates were greater for day/night temperatures <32/26.5 °C. High temperatures (32/26.5 °C) and 10% CO2 reduced bentgrass net photosynthesis by 37.5 μmol CO2/m2/s. Shoot and root total nonstructural carbohydrates also were lowest for highest temperature regime. Respiration exceeded gross photosynthesis at 32/26.5 °C when 5% and 10% CO2 injection levels were used, indicating a carbon deficit occurred for these conditions. Irrigation volume and frequency did not affect bentgrass growth. High temperatures combined with high soil CO2 levels produced poorest turf quality.