Comparison of turf performance and root systems of bermudagrass cultivars and 'Companion' zoysiagrass

The sustainability of cool-season grasses in temperate climates (transition zones) has been questioned because of a high irrigation requirement during the summer months. To reduce the amount of water used for irrigation, warm-season turf species such as Cynodon dactylon L. and Zoysia japonica Steud. have been introduced into Mediterranean countries. Research was conducted at the University of Padova, Italy to investigate several root characteristics and turf performance of four bermuda-grasses and one zoysiagrass in the transitional climate of northeastern Italy. The study included Cynodon dactylon cultivars 'Yukon', 'Riviera', 'NuMex Sahara', and 'La Paloma' and Zoysia japonica 'Companion'. Visual ratings for color and density were taken monthly during the growing season of 2007 and averaged for spring, summer, and fall. In September 2007 turf cores were collected from each plot to determine absolute values for root length density (RLD), root weight density (RWD), and root diameter in the thatch layer and at five soil depths: 0-3, 3-8, 8-15, 15-25 and 25-40 cm. Weighted means were calculated for 0-40 cm. There was no difference in RLD and RWD in the thatch layer among cultivars. 'La Paloma' had the highest RLD and RWD and 'Yukon' and 'Companion' zoysiagrass exhibited the lowest RLD and RWD for weighted means. 'Yukon' exhibited the darkest green color and 'Companion' the lightest during summer and fall. 'Yukon' and 'Riviera' provided the highest stand density and 'Companion' the lowest throughout the investigative period. Summer color correlated significantly (P<0.05) with all measured root parameters at the soil depth of 25-40 cm. Summer turf color also correlated significantly (P<0.05) with the weighted means of root length and root weight yielding correlation coefficients of 0.51 and 0.52, respectively. No correlation could be established between stand density and rooting.