Determination of Crop Water Stress Index and Irrigation Timing on Olive Trees Using a Handheld Infrared Thermometer

Leaf temperature has long been recognized as an indicator of water availability. The stress level in a plant can be quantified from leaf temperature by using the crop water stress index (CWSI). In this study, it was investigated whether infrared thermometer measurements and accordingly CWSI could be used to create irrigation schedules for olive trees (cultivated variety Memecik). The research was conducted at the olive tree plantation of the Olive Research Station between 2009 and 2010. In the study, the effects of different irrigation treatments on the yield, canopy temperature, and CWSI of olive trees were investigated, and the optimum irrigation schedule was determined according to the findings. Seven different water application treatments were created using the drip irrigation method. Five treatments consisted of irrigating at a rate equivalent to 25% (S-0.25), 50% (S-0.50), 75% (S-0.75), 100% (S-1.00), and 125% (S-1.25) of the cumulative evaporation in 5 days from a Class A evaporation pan. The other two treatments consisted of a treatment in which the humidity lost at a soil depth of 0–90 cm was replenished each time to the field capacity (Control, S-C) and a treatment in which no irrigation was performed and cultivation was carried out under completely rain-based conditions (Stress, S-0). In the study, the amounts of irrigation water applied to the treatments ranged from 0 to 809 mm, and the crop water consumption values varied from 127 to 853 mm according to the average of both years. The highest water-use efficiency was obtained in the S-0 treatment, whereas the highest irrigation water–use efficiency was obtained from the S-0.50 treatment. One of the important findings of this study was that handheld infrared thermometer can be used for stress detection and irrigation scheduling of olive trees. When the mean CWSI values in the experimental years were examined in terms of the irrigation treatments, the CWSI values ranged from 0 to 0.68 in 2009 and from 0.02 to 0.71 in 2010. In both years, the highest values were recorded in the S-0 treatment, and the lowest values in the S-1.25 treatment. When water-use efficiency is evaluated along with CWSI values, irrigation can be recommended at half of the evaporation from a Class A evaporation pan (S-0.50, when CWSI values reach 0.39). In conditions in which water sources are insufficient, it can be recommended that irrigation be started when evaporation is a quarter (S-0.25), that is, when CWSI values reach 0.49.