Evaluation of a crop water stress index for irrigation scheduling of bermudagrass Yasar Emekli *, Ruhi Bastug, Dursun Buyuktas, Nefise Yasemin Emekli Akdeniz University, Faculty of Agriculture, Department of Farm Structures and Irrigation, 07059 Antalya, Turkey 1. Introduction Efficient use of water in the Mediterranean Region is becoming an important issue due to increasing irrigation water requirements as well as environmental sustainability. Deci- sion-makers and turfgrass managers in the province of Antalya at the Southern Turkey are particularly interested in studies concerning the conservation and management of water because a large amount of water is required to irrigate the recreational and sporting facilities covered with grass in the recently build hotels and residential neighborhood. Irrigation on grass-covered areas is aimed essentially to sustain turf quality and performance by maintaining a favorable soil water level (Kneebone et al., 1992). This aim can be achieved with well-scheduled irrigation together with other appropriate inputs, such as fertilizer. Generally, irriga- tion scheduling methods fall into three categories: (1) soil based, (2) plant based, and (3) meteorologically based. The plant essentially integrates its soil and atmospheric environ- ments and reflects the prevailing conditions in growth processes. Therefore, irrigation scheduling based on plant monitoring is increasingly used (Grimes et al., 1987). As plants close their stomata because of water stress, stomatal conductivity, heat flux, transpiration and the cooling effects of evaporation decrease and the canopy temperature increases, compared to non-stressed plants. This is the basis for the use of canopy temperature to determine plant water status (Stokcle and Dugas, 1992). The energy balance on the agricultural water management 90 (2007) 205–212 article info Article history: Accepted 12 March 2007 Published on line 26 April 2007 Keywords: Bermudagrass Infrared thermometer CWSI Irrigation scheduling abstract This study was conducted to assess crop water stress index (CWSI) of bermudagrass used widely on the recreational sites of the Mediterranean Region and to study the possibilities of utilization of infrared thermometry to schedule irrigation of bermudagrass. Four different irrigation treatments were examined: 100% (I 1 ), 75% (I 2 ), 50% (I 3 ), and 25% (I 4 ) of the evaporation measured in a Class A pan. In addition, a non-irrigated treatment was set up to determine CWSI values. The status of soil water content and pressure was monitored using a neutron probe and tensiometers. Meanwhile the canopy temperature of bermuda- grass was measured with the infrared thermometry. The empirical method was used to compute the CWSI values. In this study, the visual quality of bermudagrass was monitored seasonally using a color scale. The best visual quality was obtained from I 1 and I 2 treatments. Average seasonal CWSI values were determined as 0.086, 0.102, 0.165, and 0.394 for I 1 , I 2 , I 3 , and I 4 irrigation treatments, respectively, and 0.899 for non-irrigated plot. An empirical non- linear equation, Q ave ¼ 1 þb 6½1 þð4:853 CWSI ave Þ 2:27  0:559 c , was deduced by fitting to mea- sured data to find a relation between quality and average seasonal CWSI values. It was concluded that the CWSI could be used as a criterion for irrigation timing of bermudagrass. An acceptable color quality could be sustained seasonally if the CWSI value can be kept about 0.10. # 2007 Elsevier B.V. All rights reserved. * Corresponding author. Tel.: +90 242 3106542; fax: +90 242 2274564. E-mail address: yemekli@akdeniz.edu.tr (Y. Emekli). available at www.sciencedirect.com journal homepage: www.elsevier.com/locate/agwat 0378-3774/$ – see front matter # 2007 Elsevier B.V. All rights reserved. doi:10.1016/j.agwat.2007.03.008