St. augustinegrass [Stenotaphrum secundatum (Walt.) Kuntze] is widely used as a warm-season turfgrass. This is one of the most popular turfgrass species used for home lawns throughout the southern United States. St. augustinegrass has better shade tolerance than many other warm-season grasses (Busey, 2003). There are many commonly produced cultivars of st. augustinegrass, which show different physiological and morphological responses to shade. Peacock and Dudeck (1981) reported that ‘Bitter Blue’ st. augustinegrass performed best in shade. Trenholm and Nagata (2005) reported best shade tolerance in dwarf cultivars of st. augustinegrass and optimal turf performance at 30% shade compared with 0%, 50%, or 70% in all cultivars.
Tegg and Lane (2004) reported that quality of ‘Pennlinks’ creeping bentgrass (Agrostis stolonifera L.); ‘Supranova’ supine bluegrass (Poa supina Schrad.); tall fescue (Festuca arundinacea Schreb.); a blend of ‘SR8200’, ‘Mini Mustang’, and ‘Shortstop’; and ‘C1’ bermudagrass (Cynodon dactylon L. Pers.) declined under high shade levels. They found acceptable turf quality in supine bluegrass and tall fescue under 56% and 65% shade, respectively. Wilson and Hill (1990) found that bahiagrass (Paspalum notatum Fluegge.) had greater leaf nitrogen (N) and K concentration under tree shade than in full sun.
There are management strategies to improve turf performance under shade, including increasing mowing height, reducing N fertilization and irrigation, and application of growth regulators (Harivandi and Gibeault, 1997; Qian and Engelke, 1998). Potassium has been shown to enhance turfgrass resistance to biotic and environmental stresses (Turner and Hummel, 1992). It can additionally aid in the production of starches, promote root growth, and assist in stomatal regulation (Wallingford, 1980). Potassium was found to be essential for regulatory roles that sustain plant growth and reproduction such as photosynthesis, protein synthesis, ionic balance control, and regulation of plant stomata and water use. Maximum response to K fertilization was shown to require adequate supplies of other plant nutrients (Callahan and Overton, 1978).
Snyder and Cisar (2000) found that growth of ‘Tifgreen’ bermudagrass occurred in response to K application when leaf tissue K concentration was below 13 g·kg−1 dry matter, whereas there was no increased leaf tissue K concentration or growth rate in response to additional K application when leaf tissue K concentration was 16 g·kg−1 dry matter or greater. In a study by Monroe et al. (1969), growth, clipping weight, weight of underground plant parts (root and rhizomes) and tops, vigor score, tiller counts, and blade width were increased by K application in kentucky bluegrass (Poa pratensis L.). Fitzpatrick and Guillard (2004) noted that kentucky bluegrass showed inconsistent response to K fertilization. Across varying N rates and clipping management, K application had no effect on clipping yields and turf quality although soil-extractable K levels were tested low. There were no yield or quality responses to leaf tissue K concentration (Fitzpatrick and Guillard, 2004). Trenholm et al. (2000) reported that both hybrid bermudagrass (Cynodon dactylon L. × C. transvaalensis Burtt-Davy), ‘Tifgreen’ and ‘TifSport’, and seashore paspalum (Paspalum vaginatum Swartz.), ‘Temple 1’, and ‘Sea Isle 2000’; and ecotypes HI-1, SIPV-2, and K1 exhibited improved wear tolerance with greater leaf tissue K concentration. Better visual quality and color scores, shoot density, and wear tolerance correlated with K application in two paspalum ecotypes (SIPV-2 and K1). However, Johnson et al. (2003) found that there was no significant effect of K application on creeping bentgrass quality and leaf tissue K concentration showed a weak correlation with turf quality.
‘Captiva’ is a new dwarf cultivar of St. Augustingrass that is characterized by dark green, short, narrow leaf blades and reduced vertical leaf extension. ‘Captiva’ has improved tolerance to southern chinch bug (Blissus insularis Barber) and the plant hopper (Liburnia pseudoseminigra Muir & Gifford) (Trenholm and Kenworthy, 2009). However, there is little science-based knowledge about responses of ‘Captiva’ st. augustinegrass to shade and K. This information could provide useful information for management of ‘Captiva’ under shaded conditions. The objectives of this study were to evaluate the responses of ‘Captiva’ to shade and K levels and to determine if K application could enhance tolerance of ‘Captiva’ to shaded conditions.
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