Use of infrared thermometer technique in irrigation scheduling of pomegranate (Punica granatum L.) plant

Rainfall quantity and distribution during the growing period can not meet crop water requirement in our country located in semi arid climate zone. Thus, the importance of irrigation increases gradually and irrigation has become a necessary production input. On the other hand, irrigation scheduling which means when and how much water to apply is very important in irrigation management. Irrigation can be scheduled based on soil, plant and climatic conditions. While irrigation scheduling methods based on climatic conditions and soil are still used, the method based on plant is increasingly gaining importance. The main objectives of this study are to assess crop water stress index (CWSI) and to determine irrigation schedule of pomegranate using infrared thermometer technique. For this purpose, treatments with three replications were irrigated every three and six days intervals, as much as 0.50 (S1), 0.75 (S2), 1.00 (S3), and 1.25 (S4) of Class A pan evaporation. Additionally, an unirrigated plot (S0) was also formed to derive lower baselines of basic graphic which is used to determine crop water stress index during the experiment. Before and after each irrigation, canopy temperature was measured with the infrared thermometer in all treatments between 11.00 and 14.00. CWSI was calculated by using differences of canopy and air temperature and vapour pressure defict values. Throughout the season, before each irrigation, soil moisture content and stomal resistance were measured in all treatments. The equations obtained for non water stress baseline irrigated every three and six days are Tc-Ta=0.6679VPD-3.4995 and Tc-Ta = -0.6692VPD-5.274, respectively. The equation of full water stressed upper baseline is Tc-Ta= 0.0489VPD+2.8734. There was no significant relationship between yield and CWSI values in treatments irrigated every three days. However, statistically significant correlation between CWSI values and yield in treatments irrigated every six days was obtained. S3 treatment where the highest yield was obtained was also the treatment where the lowest CWSI was obtained. According to the results obtained, it is concluded that infrared thermometer can be used for irrigation scheduling of the pomegranate plant in Antalya conditions. When using this technique in Antalya conditions, it is suggested to keep the seasonal mean CWSI value approximately 0.2 and the index value of 0.40 can be used to start the irrigation. Aditionally, it is suggested that the amount of irrigation can be determined as much as the amount of evaporation measured until the index value reach 0.40.