Use of a crop water stress index for scheduling the irrigation of sunflower (Helianthus annuus L.)

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This study was designed to evaluate different threshold crop water stress index (CWSI) values to schedule irrigation for sunflower (Helianthus annuus L.) grown under furrow irrigation. Irrigations were started when CWSI values reached 0.2, 0.4, 0.6, 0.8 and 1.0 (non-irrigation). The CWSI values were computed from measurements of canopy temperature, air temperature and atmospheric vapor pressure deficit. Total irrigation water amounts of 679, 584, 470 and 227 mm were applied to the T0.2, T0.4, T0.6 and T0.8 treatments, respectively. The maximum seasonal evapotranspiration (ET), 809 mm was measured from the T0.2 treatment. Irrigation levels significantly affected seed yield. Although the highest seed yield (4.38 t ha-1) was obtained from the T0.2 treatment, the T0.4 and T0.6 treatments were not significantly different from the T0.2 treatment. Therefore, based on these results, a CWSI value of 0.6 can be used for the irrigation time of sunflower under Tekirdağ conditions.