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  • Author or Editor: Jason Kruse x
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The effects of potassium (K) on stress tolerance of turfgrass have been documented for some environmental stresses but not for shade tolerance. ‘Captiva’ st. augustinegrass [Stenotaphrum secundatum (Walt.) Kuntze] was evaluated in this research project to determine the effects of K and shade on turf performance. The study was conducted at the University of Florida Envirotron Turfgrass Research Laboratory in Gainesville, FL. Grasses were planted in 15.2-cm plastic pots in a climate-controlled glass house. Two consecutive studies were conducted, the first from 20 May to 24 Oct. 2009 and the second from 18 Jan. to 20 June 2010. Grasses were placed in either full sun or under shade structures covered with woven black shadecloth to provide 30%, 50%, or 70% shade. Potassium was applied as potassium chloride (KCl) (0–0–62) at four rates (0, 0.6, 1.2, or 2.4 g·m−2) every 30 days. In both trials, turf visual quality and color scores and dry weight (DW) of shoot and root were lowest at 70% shade and highest at 30% shade. Turf visual quality score increased as K rate increased. Leaf length increased and leaf width decreased as shade level increased. Leaf tissue total Kjedahl nitrogen (TKN) and K concentration increased as shade level increased from 0% to 70%. Thatch DW was greatest at 70% shade and lowest at 30% shade. In the first trial, turf treated with a higher K rate had longer leaf length and greater root DW. Results from this study showed that ‘Captiva’ could maintain acceptable visual quality at up to 50% shade and that K at 2.4 g·m−2 may help turfgrass grow in a shaded environment by improving turf visual quality score, root growth, and leaf tissue K concentration. Additional field plot research should be conducted to verify these responses.

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Water management and turfgrass breeding efforts focused on water conservation can benefit from a better understanding of drought stress physiology because it relates to visual quality. In a repeated study under controlled conditions, ‘Argentine’ bahiagrass (Paspalum notatum Flugge), ‘Floratam’ st. augustinegrass [Stenotaphrum secundatum (Walt.) Kuntze], and ‘Empire’ zoysiagrass (Zoysia japonica Steud.) were subjected to drought stress as defined by the normalized transpiration ratio (NTR) of drying to well-watered plants. Differences in total water extracted from the soil as the soil dried to stomatal closure were not different among grasses; however, zoysiagrass had the slowest water use rate and less firing under increasing drought stress than the other grasses. Optical sensing of the normalized difference vegetation index from the turf canopies was not an effective predictor of drought stress for either study. In both studies, severe wilting and some firing occurred in bahiagrass and st. augustinegrass when NTR was 0.3. Zoysiagrass was not severely wilted until 0.1 NTR and exhibited little firing even after drying had continued for an additional 7 days past 0.1 NTR. After 7 days at well-watered status after drought stress to a severity of 0.1 NTR, all grasses were able to recover to an acceptable visual quality rating. This recovery from severe wilt and some canopy firing (except for zoysiagrass), indicating that a return to well-watered soil after severe stress, can result in acceptable turf recovery.

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Irrigation for commercial and residential turf is becoming limiting, and water scarcity is one of the long-term challenges facing the turfgrass industry. Potential root development and profile characteristics of turfgrass provide important information regarding their drought resistance mechanisms and developing drought-resistant cultivars. The objective of this study was to determine the potential root development and root profile characteristics of two bermudagrass species and two zoysiagrass species using experimental lines and commercial cultivars. The species evaluated in the study were: African bermudagrass (Cynodon transvaalensis Burtt-Davy), common bermudagrass (CB) [Cynodon dactylon (L.) Pers. var. dactylon], Zoysia japonica (ZJ) (Steud), and Zoysia matrella (ZM) L. Plants were grown outdoors in clear acrylic tubes encased in poly vinyl chloride (PVC) sleeves. The experimental design was randomized complete block design with four replications. Rates of root depth development (RRDD) during the first 30 days were obtained. Root length density (RLD) in four different horizons (0–30, 30–60, 60–90, and 90–120 cm) was determined 60 days after planting. Specific root length (SRL, m·g−1) was also calculated dividing total root length by total root dry weight (RDW). The root depth in four turfgrass species increased linearly during the first 30 days after planting. Common bermudagrass (CB) had high RRDD and uniform RLD in different horizons, while ZM accumulated the majority of its roots in the upper 30 cm. Z. matrella had higher RLD than CB in the upper 30 cm. African bermudagrass had higher SRL than CB. There was limited variation within the two African bermudagrass genotypes studied except at the lowest horizon (90–120 cm). Two genotypes in CB and ZJ, respectively, including ‘UF182’ (ZJ), which consistently ranked in the top statistical group for RRDD, and RLD for every horizon, and ‘UFCD347’ (CB) demonstrated greater RLDs in the lower horizons in comparison with the commercial cultivars.

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