POTASSIUM FERTILIZATION RELATED TO COLD RESISTANCE IN BERMUDAGRASS

Applications of high rates of potassium are often made in an attempt t o increase winter hardiness of bermudagrass [Cynodon dactylon (L.) Per s.] turfs. Research was conducted to evaluate two bermudagrass cultiva rs field-grown on a high sand based soil mix and a native soil for the influence of applied K on cold resistance. A field study with six K r ates ranging from 0 to 390 kg ha(-1) growing month(-1) were applied to 'Titdwarf' and 'Tifway' bermudagrass [Cynodon dactylon (L.) Pers. x C . transvaalensis Burtt Davy] established on a sand-peat (9:1 by volume ) and a Uchee loamy sand (loamy, siliceous, thermic Arenic Hapludult) during 1992-1994. Potassium chloride or K2SO4 were compared as sources of K and were applied with twice monthly N applications, Elemental so il and plant leaf tissue concentrations were measured periodically dur ing the course of the study, By means of an electrolyte leakage (EL) m ethod, predicted lethal temperatures were identified for rhizome sampl es removed from the held monthly from October through March of 1992-19 93 and 1993-1994. Lethal temperatures estimated by EL were compared wi th those obtained by means of a recovery growth method. Extractable K in the growth media (12-204 kg K ha(-1)) and leaf tissue K concentrati ons (8.9-17.3 g K kg(-1) DM) increased with increasing K rates, Applic ation of high rates of K had no effect on predicted lethal temperature s or plant regrowth, Lethal temperatures for Tifdwarf ranged from -5.8 to -7.0 degrees C, whereas those of Tifway varied from -6.8 to -8.4 d egrees C. High K rates appear to not increase bermudagrass rhizome col d resistance; therefore, there may be no benefit to using rates beyond those that provide sufficient K levels for normal growth.