The feasibility of obtaining sap flow (SF), maximum daily trunk shrinkage (MDS) and midday stem water potential (Ψstem) baselines or reference values for use in irrigation scheduling was studied in adult Fino lemon trees (Citrus limon (L.) Burm. fil.) grafted on sour orange (C. aurantium L.) rootstocks. Plants were irrigated daily above their water requirements in order to obtain non-limiting soil water conditions. The results indicated that baselines for plant-based water status indicators (MDS, SF and Ψstem) can be obtained, even though there was a certain scattering of the data points representing the relations between the plant-based measurements and the environmental variables (reference evapotranspiration, solar radiation, vapour pressure deficit and temperature). SF was more closely associated with changes in the studied evaporative demand variables than were MDS and Ψstem. SF and Ψstem were more closely correlated with changes in reference evapotranspiration (ETo) (r 2 = 0.93 and 0.79, respectively), while MDS behaviour was best correlated with mean daily air temperature (T m) (r 2 = 0.76). Increases in the evaporative demand induced more negative Ψstem values and, as a consequence, SF increased, which, in turn, was translated into an increase in MDS. This confirmed that SF and MDS were very good predictors of the plant water status during the observation period and their continuous recording offers the promising possibility of their use in automatic irrigation scheduling in lemon trees.

This research was supported by Ministerio de Educacio´ n y Ciencia (MEC), (CICYT/FEDER AGL2003-9387-C05-02 and AGL2004-0794-C03- 02) and PETRI (PTR1995-0693-OP-02-01) grants to the authors. M.F. Ortun˜ o and O. Mounzer were research fellowships from CSIC (Program I3P) and MEC (FPI), respectively.

Peer reviewed