Prediction of water status by means of an empirical model in orange bearing trees

During three consecutive years, in a citrus orchard planted with Tarocco ‘Meli’ and ‘Scirè’ 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 Ψpd utilizing stem water potential (Ψmd) and vapor pressure deficit (VPDmd) 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 ‘Scirè’. As a result, two empirical models were built. The 2nd degree equation (pd=a+b1md+b2VPDmd) was obtained by considering the pd as dependent variable, the md and the VPDmd as explanatory variables. ANOVA applied to the multiple regression resulted highly significant with P-value <0.000, indicating highly predictive capacity of the equation. The multiple coefficients of correlation were R=0.783 for Tarocco ‘Meli’ and R=0.825 for Tarocco ‘Scirè’. The two models were tested with the method of the cross-validation, a technique for estimating the performance of a predictive model. The observed data showed no statistical differences when compared to the fitted data. The results were discussed in a relation to the application of the empirical model which estimates the pd that seems to be the best indicator of tree water status, without measuring it before dawn.