Potassium Application Reduces Calcium and Magnesium Levels in Bermudagrass Leaf Tissue and Soil

High rates of potassium (K) are often applied in an attempt to increase stress tolerance of hybrid bermudagrass [Cynodon dactylon (L.) Pers. x C. transvaalensis Burtt Davy] turfs. Two field-grown bermudagrass cultivars, ‘Tifdwarf’ and ‘Tifway’, were used to determine the influence of applied K on plant nutrient content and nutrient retention in two soils. Six rates of K ranging from 0 to 390 kg·ha were applied twice per month each growing season from 1992 to 1994. The cultivars were established on both a sand-peat (9:1 by volume) and loamy sand. Potassium chloride and K2SO4 were compared as sources of K, and were applied simultaneously with N applications. Extractable soil K and leaf tissue K concentrations increased with increasing K rates. There was a critical K fertilization level (74 to 84 kg·ha) for each cultivar and medium combination beyond which no increase in tissue concentration was observed. Increasing K fertilization resulted in a decrease in extractable Ca and Mg in both media with corresponding decreases in tissue Ca and Mg concentrations. High K rates appear to increase the potential for Ca and Mg deficiencies in bermudagrass, indicating that rates higher than those that provide sufficient K levels for normal growth should not be used. Received for publication 28 Mar. 1998. Accepted for publication 13 July 1998. Journal Paper no. R06224, Univ. of Florida Agricultural Experiment Station. The cost of publishing this paper was defrayed in part by the payment of page charges. Under postal regulations, this paper therefore must be hereby marked advertisement solely to indicate this fact. native soil, on tissue nutrient concentrations of two bermudagrass cultivars, and on subsequent extractable soil concentrations of K, Ca, and Mg. Materials and Methods A 3-year study was initiated at the Auburn Univ. Turfgrass Research Center, Auburn, Ala. Two experiments using ‘Tifdwarf’ and ‘Tifway’ bermudagrasses were established in Spring 1992 on an Uchee loamy sand (loamy, siliceous, thermic Arenic Hapludult) and a sand-peat (9:1 by volume) root zone. A complete factorial combination of treatments using KCl and K2SO4, both at six rates, was applied to 4.2-m field plots. Potassium was applied at 0, 12, 24, 49, 98, and 195 kg·ha per month on the loamy sand soil and 0, 24, 49, 98, 195, and 390 kg·ha per month on the sandpeat. The study was analyzed as a split-plot in space using nested variation as an error term to measure differences between cultivars (McIntosh, 1983). Urea was applied at a rate of 49 kg·ha N on the loamy sand and 98 kg·ha on the sand-peat. Potassium and N were applied simultaneously from April through October of each year and watered in with 1.8 L·m. Because N and K rates differed, data for each medium were analyzed separately. Initial Mehlich-1 extractable K concentrations were 36 and 15 kg·ha for the loamy sand and sandpeat, respectively. Based on Auburn Univ. Soil Testing Laboratory recommendations, K concentrations were “low” for the loamy sand and “very low” for the sand-peat. Micronutrients were supplied to the sand-peat during grass establishment. Phosphorus was applied to the sand-peat at 49 kg·ha in April each year according to Auburn Univ. Soil Testing Laboratory recommendations. Neither loamy sand or sand-peat required amendment to maintain a soil pH of 6.0 ± 0.2. During the summer months, irrigation was applied as needed to maintain high-quality turf. Weed control was achieved with yearly application of 0.56 kg·ha dithiopyr [3,5-pyridinedicarbothioic acid, 2-(difluoromethyl)4-(2-methylpropyl-6-(trifluoromethyl)-S,Sdimethyl ester] in mid-March, an application of 2.24 kg·ha MSMA (monosodium acid methanearsonate) in Aug. 1992, and 0.56 kg·ha bromoxynil (3,5-dibromo-4hydroxybenzonitrile) in mid-Mar. 1994. ‘Tifdwarf’ was clipped four to five times per week at a 5-mm cutting height to represent typical golf green conditions. ‘Tifway’ was mowed four to five times per week at a 12-mm cutting height as would be commonly done for a golf course fairways and tees, and sports turfs. Clippings were removed with each mowing. Clippings were harvested in May, June, Aug., and Oct. 1993 and May and June 1994 for yield determination. Clippings of a 2-d growth over a 4.2-m area were collected in a mower catch basket and dried at 70 °C. Leaf tissue and soil samples were taken from each plot for elemental analysis between the first and fifth of each sampling month (May– October). Tissue samples were collected from following K fertilization. The monovalent cation K is absorbed and accumulated by plants much more rapidly and to a much greater degree than divalent ions such as Ca or Mg (Hannaway et al., 1980). Calcium deficiency in turfgrass has been related to increased susceptibility to diseases (Moore et al., 1961), whereas Mg deficiency reduced leaf length, shoot length, and shoot weight (Kamon, 1974). Bermudagrass is widely used on athletic fields and golf courses in the humid and warm semiarid regions of the world (Beard, 1973). High sand content in root zones of putting greens and athletic fields favors K loss through leaching during the long growing season in the southeastern United States. Thus, efficiency of utilization of applied K is thought to be relatively low. Because K absorbed by bermudagrass remains primarily in aboveground shoot tissue (Robinson, 1985), much of it is removed when the turf is mowed and clippings are removed. Thus, high K rates, or frequent K applications, may be necessary to maintain adequate K in turfgrasses grown on sandy soils. Optimum tissue K levels for bermudagrass reportedly range from 18.0 to 21.0 g·kg (Martin and Matocha, 1973). Rates of application of K required to maintain these K concentrations depend on soil type, fertility status, and N rate. Adams et al. (1967) reported that maintaining plant K concentrations >17.5 g·kg required rates of 370 and 897 kg·ha of K and N, respectively. Previous studies have not related sufficiency levels of K to tissue and soil extractable Ca and Mg levels. The objective of our research was to quantify the influence of K, applied to both a high sand-based soil and a Potassium is a primary, essential nutrient for turfgrass production. Application of K fertilizer as a cultural practice has been suggested as a means of increasing bermudagrass winter hardiness and drought tolerance (Horn, 1969; Miller and Dickens, 1995; Schmidt and Breuninger, 1981). Claims that application of high rates of K fertilizer alone can enhance stress tolerance are common in the turfgrass industry. No standard critical values or adequate concentration ranges for tissue Ca or Mg in bermudagrass have been established (Cripps et al., 1989), but tissue Mg concentration is inversely related to tissue K concentration (Belesky and Wilkinson, 1983; Landua et al., 1973; Matocha and Smith, 1980). Neither Landua et al. (1973) nor Belesky and Wilkinson (1983) reported depression of tissue Mg concentration below ≈1.0 g·kg dry weight following application of K. Matocha and Smith (1980) and West and Reynolds (1984) reported that Ca concentrations in bermudagrass and tall fescue (Festuca arundinacea Schreb.) tissue were not reduced by K fertilization, whereas Cripps et al. (1989), Razmjoo and Kaneko (1993), and Sartain (1993 ) reported decreases in turfgrass Ca and Mg content