Increasing emphasis on irrigation and water use in turfgrass has superintendents paying closer attention to the ways they use water in putting green management. As we seek to manage turf with less water, potassium (K) might be a tool, as it is thought to reduce turfgrass stress from drought. Researchers at the University of Florida studied these combined variables, examining various nitrogen to potassium (N/K) ratios on established bermudagrass putting greens, all of which were watered via different irrigation schemes.
For three different three-week periods (two in spring and one in fall), Tifdwarf and TifEagle hybrid bermudagrasses managed as a putting green were irrigated at rates of 25%, 50% or 100% of potential evapotranspiration (ETo), with irrigation applied each day. Within these main blocks of irrigation and bermudagrass cultivar were the N/K ratios, with potassium chloride (KCl) as the K source. Ratios were 1N:1K, 1N:2K, 1N:3K and 1N:4K, with the nitrogen applied at 1 pound/1,000 square feet (4.9 grams/square meter) at the start of each experimental period. Thus, K rates (expressed as K and not K2O) were 1, 2, 3 and 4 pounds/1,000 square feet (4.9, 9.8, 14.7 and 19.6 grams/square meter) for each of the ratios given above. The granular fertilizer sources were applied and watered in thoroughly before irrigation treatments began. Collected data included leaf wilting, turfgrass quality, volumetric water content, shoot density, leaf density (leaves per shoot), thatch depth and root depth.
In the first run of the experiment (spring 2009), irrigation of the bermudagrasses at only 25% ETo was too severe, and the plots suffered from drought stress. In fact, supplemental irrigation had to be applied to these plots to prevent turfgrass death. Unacceptable wilting (>10% wilting) was also observed at the 50% ETo irrigation rate, with wilting of around 34% observed in the bermudagrasses. In 2010, wilting was observed even at the 100% ETo irrigation rate, with 27% wilting for Tifdwarf and 35% for TifEagle. Regardless of the irrigation rate, the bermudagrasses wilted more than zoysiagrass and seashore paspalum, which were also in this study. Zoysiagrass and seashore paspalum could be maintained at acceptable quality at 50% ETo, while the bermudagrasses could not.
Did adding extra K help the bermudagrass withstand drought? The answer was no. Zip. Nada. Zilch. Turfgrass quality was not affected by N/K ratio, the interactions of N/K ratio and irrigation, or N/K ratio and cultivar. In other words, neither the main effect of K, the interactions of K and irrigation, nor K and cultivar had any impact on bermudagrass quality. Chlorophyll index and normalized difference vegetation index (NDVI) readings were also unaffected by N/K ratio, as were any of the other variables studied. In this study, adding extra K imparted no value at all to an improved sward of turfgrass, and there was no reason to apply K in excess of a 1N:1K ratio. In order to maintain a high-quality putting surface, the bermudagrasses studied in this project did require irrigation at or above 100% ETo (over extended periods of time with no rainfall). However, increasing K in relation to N failed to increase drought resistance, and its application provided no additional benefits.
Source: Rowland, J.H., J.L. Cisar, G.H. Snyder, J.B. Sartain, A.L. Wright and J.E. Erickson. 2014. Drought resistance of warm-season putting green cultivars on U.S. Golf Association root zones with varied potassium. Agronomy Journal 106:1549-1558.
Beth Guertal, Ph.D., is a professor in the Department of Crop, Soil and Environmental Sciences at Auburn University in Auburn, Ala., and the editor-in-chief for the American Society of Agronomy. She is a 20-year member of GCSAA.