During three consecutive years, in a citrus orchard planted with Tarocco 'Meli' and 'Scire' on sour orange ( C. aurantium L.) were verified the differences of the plant water status and the possibility to build an empirical model to estimate the psi pd utilizing stem water potential (psi md) and vapor pressure deficit (VPD md) measured at midday. The first results showed statistical differences during the irrigation season in the two clones water potential. These difference permitted to separate the data of Tarocco 'Meli' and 'Scire'. As a result, two empirical models were built. The 2nd degree equation (Psi pd=a+b 1Psi md+b 2VPD md) was obtained by considering the Psipd as dependent variable, the Psi md and the VPD md as explanatory variables. ANOVA applied to the multiple regression resulted highly significant with P-value
