Comparison of changes in stem diameter and water potential values for detecting water stress in young almond trees

Trunk diameter fluctuations (TDF) and the leaf water relation parameters, predawn and midday leaf water potential (Ψpd and Ψmd), midday stem water potential (Ψst) and midday leaf conductance (gl) were compared for use in detecting water stress and for helping with irrigation management in young almond trees. TDF were monitored throughout 2002 in three irrigation treatments: T1 (control), irrigated at 120% of crop evapotranspiration (ETc), T2, at 60% ETc for the whole year and T3, irrigated at 100% ETc except between 3 June and 15 September, when 40% ETc was supplied. The annual reference crop evapotranspiration and rainfall during the experiment were 1375 and 320 mm, respectively, while the amount of water applied in the treatments was 3165, 1525 and 1430 m3 ha−1 year−1 for T1, T2 and T3. These irrigation treatments had Ψst that varied over the season from around −0.65 to −1.0; −0.9 to −1.3 and −0.7 to −1.5 MPa, respectively. Two parameters were obtained from the TDF measurements: (i) maximum daily trunk shrinkage (MDS) and (ii) trunk growth rate (TGR). The MDS values were influenced by the evaporative demand and varied greatly between trees (CV around 10-35%). Although all the water status indicators showed a response to the water supply, the greatest changes were observed in Ψpd, Ψst and TGR. The results obtained indicate that MDS and TGR were sensitive to water stress and that TGR is the most useful parameter for quantifying water deficit intensity and duration, its behaviour being very similar to that of Ψpd and Ψst. It is concluded that TGR is useful as an indicator of stress and could serve for making irrigation decisions in young almond trees.