ROOTING CHARACTERISTICS AND ASSOCIATED DROUGHT RESISTANCE OF ZOYSIAGRASSES

Declining availability of water for landscape irrigation has increased the need for drought-resistant turfgrasses. Though drought-resistance mechanisms are known to include deep rooting in some plants, little i s known concerning zoysiagrass rooting characteristics. This study was conducted to determine if differences in rooting parameters exist amo ng zoysiagrasses, and if they are associated with drought resistance. Twenty-five zoysiagrasses cultivars and species [Zoysia japonica Steud ., Z, matrella (L.) Merr., and Z.japonica Steud. x Z. tenuifolia Willd . ex Trin.] were studied in palyethylene tubes in a glasshouse. Differ ences were observed for average maximum root depth (AMRD), total root weight, and root numbers and weights at increasing 100-mm depth increm ents. Average maximum root depth was positively correlated with total root weight and root number and weight at increasing 100-mm depth incr ements. Grasses with superior AMRD, total mot weight, and root numbers at deeper profile depths (300-500 mm) included QT2047, EI Toro, DALZ8 512, TC5018, Meyer, DALZ8514, and DALZ8516. In a previously reported f ield experiment, 11 of the 25 zoysiagrasses were rated for percent of plot area covered by green turfgrass (an indicator of drought resistan ce) under three levels of irrigation (0, 35, and 100% of turfgrass eva potranspiration [ET]). Average maximum root depth, total root weight, and root numbers at 200-, 300- and 400-mm depths in polyethylene root tubes were positively correlated with percent green plot fever in the field under deficit irrigation (0 and 35% ET), indicating that rooting depth, weight, and branching at lower depths are important drought-re sistance mechanisms in zoysiagrasses.