Using the Water Stress Index for Tomato Irrigation Control

Abstract

The temperature of the leaf surface of plants can be used as an indicator of the water stress of agricultural crops. Since plant temperature is affected by weather factors, it is usually expressed through the crop water stress index (CWSI). To calculate the CWSI, two input parameters must be known that relate plant temperature under and without maximum water stress to the water vapor pressure deficit. These basic equations are specific to each culture and locale. Many studies on the definition of CWSI and basic dependencies for tomatoes have been conducted abroad, such a study has not yet been conducted in Ukraine. The purpose of the research is to establish CWSI values and basic equations that are needed for the purpose of watering tomatoes in the south of Ukraine under subsurface drip irrigation. The paper presents the results of determining the theoretical and empirical water stress index of tomatoes under subsurface drip irrigation. The research results confirm that the water stress index can be used to plan the irrigation of tomatoes both independently and in combination with other methods to increase the accuracy of decision-making. An analysis of the daily dynamics of the CWSI was carried out, according to the results of which it was established that in the morning hours the water stress index on average during the observation period was almost 0, then, as the intensity of solar radiation increased, the CWSI also increased and reached its maximum value (1,08) at 20:00. The correlation coefficient between the water stress index and the intensity of solar radiation was 0,63. The relationship between irrigation rate, soil moisture, change in plant stem diameter, and CWSI was established, the correlation coefficients are -0,60, -0,55, and -0,51, respectively. Theoretical and imperial methods estimate CWSI equally, there is a high correlation between both methods (r=0,92). It is necessary to prescribe irrigation or increase the irrigation rate according to the theoretical and empirical methods of determining CWSI, respectively, for its values of 0,3 and -2,2. The empirical method of calculating CWSIE using the resulting equations is easier to use. The CWSI values obtained for tomatoes in this study are closely correlated with the other irrigation methods.

Evaluation of Crop Water Stress Index (CWSI) for High Tunnel Greenhouse Tomatoes under Different Irrigation Levels

“…In our study, the equation given above to predict the yield as a function of CWSI can be a useful tool for such goals. Also, this result agrees with many other studies of different crops [26,30,59,60] I120, 0.09 in I100, 0.16 in I80, and 0.23 in I60. High temperature and low relative humidity values in the high tunnel greenhouse, which was irrigated once a day, increased the plants' irrigation needs.…”

“…= 2.86-1.96 VPD [29], Tc−Ta = 1.21-1.31 VPD [30], Tc−Ta = −0.842-2.591 VPD [26]. In the study conducted by the researchers, if the VPD increased by 1 kPa, the Tc−Ta value decreased by 1.96 °C [29], 1.31 °C [30], and 2.59 °C [26].…”

“…Researchers reported the following relation for the lower limit in tomato crops: Tc−Ta = 2.86-1.96 VPD [29], Tc−Ta = 1.21-1.31 VPD [30], Tc−Ta = −0.842-2.591 VPD [26]. In the study conducted by the researchers, if the VPD increased by 1 kPa, the Tc−Ta value decreased by 1.96 °C [29], 1.31 °C [30], and 2.59 °C [26]. In the study, the decrease was determined as 2.51 °C.…”

“…Critical crop water stress index (CWSI) values should be determined for a particular crop in different climates and soils for yield prediction and irrigation management [16]. To calculate the CWSI, two input parameters must be known that relate plant temperature under and without maximum water stress to the water vapor pressure deficit [26]. The crop water stress index is the most frequently used index to quantify crop water stress based on canopy surface temperature [27].…”

“…Research has been conducted to evaluate the application of the CWSI in irrigation scheduling for different crops in different places: Sezen et al [25] red pepper, Çolak et al [1] eggplant, Kovalenko and Zuhuravlov [26] tomatoes, López-López et al [30] husk tomatoes, Bartzanas et al [31] tomatoes, Erdem et al [16] bean, and Erdem et al [32] broccoli. However, little research has been carried out to evaluate the CWSI for greenhouse crops in Turkey, especially the Central Anatolian part, where crop water stress is frequent and pervasive.…”