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The effects of various environmental factors such as soil water potential ‘( ?, KPa), vapor pressure deficit (VPD, KPa), canopy-air temperature difference(T -T ,‘C) on the leaf water potential ( ?, MPa) of sweet lime with drip irrigation metod were evaluated. Leaf water potenial did not show great sensitivity to soil water potential during short irrigation periods because of the low variations in soil moisture, whereas the leaf water potential showed great sensitivity to vapor pressure deficit which is one of the most effective factor in transpiration and water loss by plants. A linear relation between leaf and soil water
potentialsresulted with a correlation coefficient (r) of 0.503 (‘Il = 0.084 1’s—0.822) whereas the relation between leaf water potential and vapor pressure deficit is a second order equation (?1 = 0.0706(VPD)2 — 0.726(VPD) + 0.161) with a correlation coefficient of 0.789 . Also a relation between leaf water potential and the canopy
-air temperature difference was obtained as a second order equation [(Tc-Ta)= 2.187’P
+ 11.53’Pl + 9.8)]with a correlation coefficient of 0.593, whereas a multi-variable linear equation with a correlation coefficient of 0.837 between leaf water potential, vapor pressure deficit, canopy—air temperature difference and soil water potential
(?1 = 0.036 ‘?s— 0.262(VPD) — 0.075(Tc—Ta)— 0.36)I was resulted. A linear equation with a coefficient of 0.46 between crop water stress index (CWSI) and leaf water
potential was obtained (?1 = -1.614 (CWSI) — 1.425) and when the vapor pressure deficit was introduced to the model, the correlation coefficient was increased to
0.801 (?1 = —1.32 (CWSI) — 0.141 (CWSI)— 0.86).