shohre zivdar

The aim of this study was to assess the crop water stress index (CWSI), derived from leaf temperature using infrared thermometer measurements, to investigate the water stress status and irrigation timing of olive trees. Fpr this purpose a regression function was determined between crop water stress index and relative water content of leaf (RWC) and soil water content (SWC). The experimental treatments involved two olive cultivars (Koroneiki and T2) and four water regimes (irrigation of 100, 85, 70 and 55% of crop water requirement). The results showed that the non-water stressed baseline is varied throughout the study period as well as during the day. The daily variations of non-water stressed baseline were mainly due to variations in the intercept of the non-water stressed baseline that can be explained by variations in zenith solar angle. After investigating the relationship between vapor pressure deficit (VPD) and the difference between crop and air temperature (), the equation of Tc-Ta = -0.45 VPD+1.06, r2 = 0.99 was determined for the non-water stressed baseline of the olive trees at 12:30 pm. The effect of irrigation regime on water stress index of Kroneiki and  olive trees was not significant in none of the measurements during the study period. However, crop water stress index was significantly correlated with relative water content (Kroneiki: r2=0.67**, : r2=0.88**) and soil water content (Kroneiki: r2=0.74**, : r2=0.78**). Therefore, the crop water stress index is a good indicator of the water stress status of the Koroneiki and T2 olive trees.

Spectrometric measurements have the potential for fast and non-destructive measurements of plant water stress. The aim of this work was to investigate the ability of several spectral water indices, including water index (WI), normalized spectral water indices 1-5 (NWI 1-5), and normalized water index based on wavelengths in 960 and 940 nm (NWI 960-940) for detection of water stress in olive trees. The experimental treatments involved two olive cultivars (Koroneiki and T2) and four water regimes (100%, 85%, 70%, and 55% of crop water requirement). Results showed that the olive trees in different water supplies 85%, 70%, and 55% of ETc were subjected to soil moisture deficit equal to 11, 15, and 20%, respectively, as compared to soil moisture of control treatment. Because of the high resistance of olive trees to water stress, water reduction at levels of 15, 30, and 45 percent did not have significant effects on spectral indices. However, spectral indices were closely and significantly linear associated with relative water content of the crop leaf (). Among all tested water spectral indices, NWI-2 showed the least consistent associations with relative water content of the leaf (ranging from 1–23% less than the ones in other tested indices). Based on the average amount of spectral indices and relative water content during the study period, NWI4, NWI5, NWI1, WI, NWI960-940, NWI3, and NWI2 showed a stronger relationship with the relative water content of olive leaves, respectively. In conclusion, spectral reflectance indices, WI, NWI 1-5, and NWI 960-940, could be useful for fast and non-destructive estimating of plant water stress.