Determination of Irrigation Time by Utilizing Plant Water Stress Index (CWSI) Values of II. Crop Sesame Genotype in Siirt Conditions
Abstract
This research was carried out to determine the plant water stress index (CWSI) by using infrared thermometer (IRT) data calculated as a result of leaf crown temperature measurements of the second crop sesame plant grown in semi-arid climate conditions in Siirt, and to determine the relationships between irrigation time and seed yield of sesame plant and CWSI by using these index values. In this study, the irrigation program was established to reintroduce 100 % (I ), 70% 100 (I ), %35 (I ) of the decreased water through the effective root depth of 90 cm every 7 days. Thus, a full irrigation (I ) and 70 35 100 irrigation with 2 different levels of stress (I and I ) were created. In the research, a total of 575.00 and 576.66 mm of 70 35 irrigation water was given to I100 (control) irrigation in the first and following years, respectively. The water consumption of the above-mentioned subject was determined as 606.00 mm in the first year and 646.33 mm in the second year of the study. The yield per hectare in the first year of the research on the aforementioned irrigation was 1110.34 kg; In its second year, it was determined as 1319.00 kg. In the first and second years of the study, the lower limit (LL) values for the absence of water stress needed to determine the plant water stress index were Tc-Ta=0.373-2.42 VPD and Tc-Ta=0.74-2.52 VPD, respectively; The upper limit (UL) values, where the plant is completely water stressed, were determined as 2.04 °C and 1.77 °C, respectively. From the infrared thermometer measurements at the time of irrigation, the threshold plant water stress index value, where sesame seed yield starts to decrease, was calculated as 0.31. On the other hand, it was determined that there is a negative linear proportionality between sesame seed yield and plant water stress index values.
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Introduction
Jackson et al. (1982), explained how to make leaf crown temperature (vegetation temperature) measurements with infrared thermometer device, which is accepted as an indicator of plant water stress index, and what should be consideredIt is stated that the temperature of the plant leaf crown can be measured with a portable infrared thermometer and the device should beheld at an angle of 30 °C from the ground at the time of reading and it should be covered with 80% vegetation in order to make accurate measurements. The internal water status of plants; It has been reported that neither soil water content nor atmospheric demand can be determined as accurately as the plant water stress index (CWSI) (Reginato and Howe, 1985). Therefore, methods aiming to determine the internal water status of plants are used by many researchers in making irrigation plans (Reginato and Howe, 1985; Yazar, 1993). In a study, it was determined that the slope and intersection of the lower limit threshold without water stress increased until the vegetation reached 70 %. It was found that the slope of the lower boundary line without water stress and the correlation coefficient obtained from measurements under conditions where the crown temperature was greater than 27.4 °C were greater than that obtained from daily measurements (Wanjura et al., 1990). Gençoğlan (1996), in his study to prepare an irrigation program by using the CWSI determined from infrared thermometer (IRT) and porometer observations in Çukurova conditions, found that the grain yield started to decrease and the threshold CWSI value determined from infrared observations before irrigation was 0.19 and the threshold value determined from porometer observations was 0.26 reported that there will be no yield loss in irrigated corn under these conditions. Fischer (2001) reported that the leaf crown temperature (cover temperature) of the plant is an important criterion determining the difference from the ambient air temperature and that the leaf crown temperature is lower than the air temperature. The plant water stress index was developed from the relationship between the crown temperature and the air temperature difference versus the vapor pressure gap of the air. When the plant reaches a certain water stress index value, it should be watered. This threshold value varies from plant to plant, climate and cultivation techniques (Çolak et al., 2012). Gençel (2009), in his study to prepare an irrigation program by making use of the CWSI values. It was determined that the grain yield started to decrease, the threshold CWSI value determined from infrared observations before irrigation decreased to 0.35-0.40 (just before irrigation) in the most frequently irrigated I40 subject and to 0, which was the lowest value approximately two days after irrigation. Tanriverdi (2010) reported that Water Stress Index (WSI), or WSI and Water Deficiency Index (ADI), are useful tools that can be used to optimize irrigation time. It has been reported that the water stress present in the plant can be determined quantitatively by using some measurement and observational criteria. It can be said that these parameters are the difference between the plant crown and the air temperature and the vapor pressure gap of the air (Jackson, 1981). Moroni et al. (2012) emphasized that the fastest and most accurate method for measuring water stress is the canopy (leaf-crown) temperature (CWSI). In general, the decrease in soil moisture before irrigation has an effect on increasing the plant crown temperature values, and the CWSI values are higher with the decreasing moisture in the soil (Kırnak and Gençoğlan, 2001). It has been reported that the CWSI value determined by using the lower (LL) and upper limit (UL) lines, which are found theoretically and experimentally, varies between zero and one (Gençoğlan and Yazar, 1999). Çamoğlu et al. (2011) stated that leaf water content values can be used in the instant determination of plant water stress. Some researchers stated that the leaf crown temperature determined as a result of IRT measurements and the plant water stress index calculated by using these values can be used in the preparation of irrigation plans (Clawson and Blad, 1982). On the other hand, Nielsen and Gardner (1987) reported that the irrigation time can be determined by using the plant water stress index values, but the amount of irrigation water to be applied cannot be determined with the aforementioned method. The aim of this study is to determine the CWSI by using the leaf crown temperature values measured in the second crop sesame plant grown in Siirt conditions in 2016 and 2017, to determine the stress threshold line (watering time of sesame) where the decrease in yield begins, and to determine the relationship between grain yield and plant water stress index.
Conclusion
AND SUGGESTIONS This work; Afield study was conducted in semi-arid climate conditions in order to determine the plant water stress index of the sesame genotype grown in water-free and water-stressed conditions and to determine the threshold value at which the economic yield reduction will start from the residual sesame plant by making use of these data. As a result of the findings obtained from the research, II. When the plant water stress index threshold value of the crop sesame plant is 0.31, it can be decided that the irrigation time has come, and when irrigation is done when it is 0.31, there will be no statistically significant loss in yield, and it has been determined that 30% water reduction can be made in conditions where irrigation water is limited. It has been determined that if the CWSI is higher than the value mentioned above, there may be a significant decrease in yield. In the light of the data obtained from the study, yield estimation can be made by making use of the linear relationships between the sesame grain yield and the plant water stress index obtained by using the leaf crown temperature measurements made at the irrigation time.
